The role of the Sun in the spread of viral respiratory diseases


Research News


Why do most viral epidemics spread cyclically in autumn and winter in the globe’s temperate regions? According to an interdisciplinary team of researchers of the Italian National Institute for Astrophysics, the University of Milan, the Lombardy regional agency for the environment and the Don Gnocchi Foundation, the answer is intimately related to our Sun: their theoretical model shows that both the prevalence and evolution of epidemics are strongly correlated with the amount of daily solar irradiation that hits a given location on the Earth at a given time of the year. The work of the Italian team was recently published in the iScience journal.

“Our model offers a simple answer to an important, yet still unsolved, scientific question”, says Fabrizio Nicastro, INAF researcher and PI of the work. “Why do many viral respiratory epidemics, such as influenza, develop cyclically during autumn and winter only in the temperate regions of the globe’s northern and southern hemispheres, while they seem to be present at all times – albeit with lower prevalence compared to the seasonal cycles in the temperate regions – in the equatorial belt? And what triggers and determines such seasonality? In our work, we propose that what causes the seasonality of airborne-transmitted epidemics is exactly the same mechanism that causes seasons on our Planet: the amount of daily solar irradiation on the Earth”.

It is well known that ultraviolet (UV) light is able to deactivate viruses and bacteria of many different kinds. The solar UV light that reaches the Earth must therefore have some disinfecting power on the exposed parts of the Planet. The efficiency of the UV deactivation of a particular virus or bacterium depends on the virus or bacterium itself, but, for a given location on Earth, it is undoubtedly greater when the solar irradiation is stronger (summer) and lower when the solar irradiation is weaker (winter). Such cyclicality of the solar disinfecting action, with annual frequency, is able to constructively resonate with another frequency typical of epidemics: the loss of immunity of the virus’s host due to its antigenic shift/drift. The combination of these two mechanisms triggers the seasonality of epidemics, on timescales that range from a few years to tens of years, depending on the antigenic frequency.

The model proposed by the Italian researchers reproduces the seasonality observed in different locations of the Earth accurately for epidemics with an intrinsic reproductive number (R0) lower than about 2 – an influenza typically has R0~1 – and is also able to model epidemics with a much larger intrinsic reproductive number, such as the current SARS-CoV-2 pandemic with R0?3-4. These models predict high-intensity intermittent initial cycles, which eventually stabilize (on timescales that depend on the antigenic-shift frequency) onto seasonally-synchronized, moderate-intensity annual cycles.

“From an epidemiologic point of view, these models clarify an important and long-standing mystery: why do influenza epidemics disappear every year when the number of susceptible individuals is still very far from that needed to trigger the herd immunity mechanism?”, adds Mario Clerici, Immunologist at the University of Milan and the Don Gnocchi Foundation.

“The Italian data of the SARS-CoV-2 pandemics can also be described accurately by our model – concludes Nicastro – but the predictive power of the model depends critically (other than on the implementation of new restriction measures) on the exact UV-B/A lethal doses for the Covid-19 virus, which our collaboration is about to measure”.


This work has been published by the iScience journal, in the article Forcing Seasonality of Influenza-like Epidemics with Daily Solar Resonance, by Fabrizio Nicastro, Giorgia Sironi, Elio Antonello, Andrea Bianco, Mara Biasin, John R. Brucato, Ilaria Ermolli, Giovanni Pareschi, Marta Salvati, Paolo Tozzi, Daria Trabattoni, and Mario Clerici.

From EurekAlert!

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November 3, 2020 2:29 am

Err, why would you bother?
We know that colds and flu are more prevalent in winter. We’ve known it for millennia.
We won’t be able to change anything to magically stop it happening.

I’m guessing they conducted this research just because they could get funding for it,
Looks like a waste of taxpayers’ money

Reply to  OldCynic
November 3, 2020 2:37 am

UV radiation kills virus

Reply to  Vuk
November 3, 2020 8:35 am

This UV “modelled” solution seems highly contrived.

their theoretical model shows that both the prevalence and evolution of epidemics are strongly correlated with the amount of daily solar irradiation that hits a given location on the Earth at a given time of the year.

As we are often reminded, correlation is not proof of causation.

daily solar irradiation also determines outside temperatures. Has anyone ever noticed how it tends to be colder in winter?

What happens when it gets cold? People heat their living and working spaces. Specific humidity ( actual molecules of water vapour ) is very low in winter due to cold outside air. When that cold air is heated, relative humidity plummets. Inside air gets very “dry” and this is not healthy for our mucus membranes. Also dry membranes will absorb any virus laden droplets with come into contact with them. Far more than if the same membrane was healthy and wet.

There is ample published studies on how influenza thrives in warm dry air.

So if their hypothesis was right influenza would be safest up until 21st December, then increasingly under attack.

If it is due to domestic heating habits, this will peak in January and February, the coldest months in the northern winter.

Now go and look at the timing of the annual influenza epidemics and see whether it peak at the winter solstice or in the thermal depths of winter.

This year, last winter’s flu season was still tailing off in March when SARS-COV2 hit us.

IMO this has more to due with domestic heating habits than UV.

I heat to 12-14C in winter and NEVER get colds and flu. YMMV.

Zig Zag Wanderer
Reply to  Greg
November 3, 2020 2:28 pm

And is vitamin D a factor? The more vitamin D, the greater the immunity, perhaps?

Reply to  Zig Zag Wanderer
November 4, 2020 1:50 pm

Good point. We know Vit D deficiency is prevalent in pts with severe covid. And Vit D levels correlate with UV light exposure.

And we know people with higher UV-blocking melanin in there skin are suffering worse in this epidemic.

Together, these “facts” suggest the seasonality is not so much due to the direct virus-killing property of UV as it is to the Vit D generation by UV exposure.

Doug Huffman
Reply to  Vuk
November 3, 2020 9:47 am

Prolonged UV-C kills virus

John Tillman
Reply to  Doug Huffman
November 3, 2020 11:46 am

However, UVC doesn’t reach the surface, thanks to the ozone which it makes and breaks.

UVB and UVA may also destroy some viruses but take longer. UV does however make vitamin D in the skin. In winter, there is less and people are more bundled up.

Another reason for viral seasonality is that people spend more time indoors in winter, with worse ventilation.

Reply to  Vuk
November 3, 2020 11:11 am

Vuk said “UV radiation kills virus”
It can also speed up death for humans.
To much of anything is not good for our wellbeing .

Ultraviolet Light Induced Generation of Reactive Oxygen Species
T L de Jager 1, A E Cockrell 1, S S Du Plessis 2
Affiliations expand
PMID: 29124687 DOI: 10.1007/978-3-319-56017-5_2
As ultraviolet (UV) radiation is naturally and ubiquitously emitted by the sun, almost everyone is exposed to it on a daily basis, and it is necessary for normal physiological function. Human exposure to solar UV radiation thus has important health implications. The generation of reactive oxygen species (ROS) by UV radiation is one of the mechanisms through which UV light can manifest its possible detrimental effects on health. When an imbalance develops due to ROS generation exceeding the body’s antioxidant defence mechanisms, oxidative stress can develop. Oxidative stress can lead to cellular damage (e.g. lipid peroxidation and DNA fragmentation), apoptosis and cell death. Broadly UV can induce ROS by affecting the cellular components directly or by means of photosensitization mechanisms. More specifically UV light can induce ROS by affecting the enzyme catalase and up-regulating nitric oxide synthase (NOS) synthesis. It may also cause a decrease in protein kinase C (PKC) expression leading to increased ROS production. UVR is capable of modifying DNA and other chromophores resulting in elevated ROS levels. The effects of raised ROS levels can vary based on the intracellular oxidant status of the cell. It is therefore important to protect yourself against the potentially harmful effects of UV light as it can lead to pathological UV-induced ROS production.,body%27s%20antioxidant%20defence%20mechanisms%2C%20oxidative%20stress%20can%20develop.

Reply to  OldCynic
November 3, 2020 2:50 am

Yes and no. There’s a correlation between epidemics and seasons, and there’s a correlation between seasons and UV, but putting it into a model doesn’t mean that UV affects epidemics. But if we forget about models and just work on what does affect epidemics, then UV is something that should be included in the studies. OK, that’s not really a ‘yes’ and a ‘no’, it’s more of a ‘no’ and a ‘don’t write it off quite yet but scrap the models’.

son of mulder
Reply to  Mike Jonas
November 3, 2020 3:37 am

Vitamin D also increases in the sunshine and reduces in the winter.

A C Osborn
Reply to  son of mulder
November 3, 2020 6:15 am

Previous studies have proved it, the 2006/2008 study was very good.

Reply to  son of mulder
November 3, 2020 6:37 am

I’ve always been a believer in the vitamin D link but the sudden onset of this second wave has puzzled me. I can’t see that vitamin D levels could drop off so fast across a long range, North-South.If these guys can establish the destructive power of UV it may provide an option for disinfection that helps for many different viral ilnesses.

A C Osborn
Reply to  john harmsworth
November 3, 2020 1:29 pm

UV has been used since the 1940s, in those days it was use to Irradiate the blood of Polio and other patients.
A bit like a dialysis machine today.

But is also under development for other treatments now.

Zig Zag Wanderer
Reply to  john harmsworth
November 3, 2020 2:33 pm

I can’t see that vitamin D levels could drop off so fast across a long range, North-South.

I’m pretty sure that forcing people to remain indoors for months will reduce UV exposure & thus vitamin D.

In Australia in the north, we’ve had almost no locally sourced infections, only imported ones. We get a lot of sun, especially in the winter, and people stay in it because it’s (relatively) cool.

Reply to  john harmsworth
November 4, 2020 1:00 am

More than 40% of adults are vitamin D deficient. The study linked below underestimates the number for two reasons:
– it uses 20 ng/ml as the upper limit of deficient. It really should be more like 30-40.
– It doesn’t control for time of year or latitude.

In the northern US, nearly 90% of adults are deficient at any time of year.

Reply to  son of mulder
November 3, 2020 8:13 am

It is possible that all Covid19 vulnerable people in England will be provided with a free supply of vitamin D

Reply to  Vuk
November 3, 2020 10:07 am

Vitamin D supplements are already cheap for a 3-4 month supply…less than a pack of smokes. Probably getting the message out that things like Vitamin D, C, Zinc et al and a healthy immune system is the first best defence against any cold or flu virus. In fact, I am amazed there hasn’t been a public information blitz about this, instead of just the ‘dark winter’ we are facing.

Zig Zag Wanderer
Reply to  Vuk
November 3, 2020 2:35 pm

Earthling2, colour me cynical, but that may be because there’s no money in vitamin D supplements.

Reply to  OldCynic
November 3, 2020 4:50 am

“We’ve known it for millennia.”

It’s called influenza because of the influence of … God knows what.

UV, time outdoor, temperature, humidity, all of the above.

Reply to  niceguy
November 3, 2020 8:11 am

Influence: Italian for “diseases (as in influenza di febbre scarlattina -scarlet fever)” taken from astrology: “streaming ethereal power from the stars when in certain positions, acting upon character or destiny of men”

Reply to  Vuk
November 3, 2020 11:12 pm

Yeah right, it’s the cosmic influence. These beasts have relativistic speeds!

I say we make a model with ionisation showers and viruses.

Michael S. Kelly
Reply to  OldCynic
November 3, 2020 6:32 pm

UV-C kills the coronavirus, and UV-C germicidal lamps are used in hospital HVAC ducting routinely just for the purpose of killing pathogens. Their sweet spot emission is above the wavelength that produces ozone. It is a mystery why germicidal lamps aren’t becoming ubiquitous, though perhaps it’s because no one has made any measurements of airborne coronavirus concentration in enclosed spaces. Actually, that’s the bigger mystery to me. When attempting to get a handle on virus contagion, why no one would make a measurement of any kind of airborne concentration under varying conditions is just mind-boggling to me.

Jon-Anders Grannes
Reply to  OldCynic
November 5, 2020 10:08 am

Migrate to Equator?

November 3, 2020 2:33 am


– Does it mean that, finally, the vitamine D is useless ? (Only direct UV on virus have an impact ? )
– Is it really explaining why viral respiratory epidemics in a tropical region occuring all the year ?

Thanks in advance,

(sorry for my english, I am french)

Dodgy Geezer
Reply to  Climarco
November 3, 2020 3:01 am

Votre anglais etre certainement melior que mon francoise comme un eleve…

Reply to  Dodgy Geezer
November 3, 2020 8:41 am

mon francoise ? Sans déconner !

Krishna Gans
Reply to  Greg
November 3, 2020 9:28 am

Vachement, deux mots, trois erreurs possibles 😀
Ma Françoise
Mon François
Mon Français

Reply to  Climarco
November 3, 2020 4:29 am

This is tricky.

It could be that Vitamin D is the whole story and the disinfecting effect of UV is irrelevant. That would be an example of a lurking variable. Except … UV is what causes the skin to make Vitamin D. So, the correlation could be correct and the mechanism could be wrong.

It could be that the disinfecting effect of UV is somewhat important but other effects are more important. A Spanish study demonstrated that calcefediol (a metabolite of Vitamin D) is a highly effective treatment for the Wuflu. That gives credence to all the studies showing that Vitamin D deficiency is highly correlated with Wuflu infection.

There is also the fact that people spend much more time cooped up indoors in the winter. Poor ventilation and proximity to others increase the viral exposure.

I’m skeptical that UV disinfection plays the biggest role in the decrease in viral infections in the summer.

Reply to  commieBob
November 3, 2020 6:56 am

I understood that UVA and B were not sufficiently energetic to have the desired effect whereas UVC is. UVC is used extensively to sanitise surfaces but, unfortunately for this paper, it does not get past the Mesosphere.

Reply to  commieBob
November 3, 2020 9:34 am

Also, thanks to shutdowns and quarantines, people were couped up when they normally would be out going parks, ballgames ect.

Krishna Gans
Reply to  Climarco
November 3, 2020 7:01 am

I remember well the time, French people didn’t like to speak English or German 😀
In so far, you are on a very good way 😀
C’était mieux d’apprendre Français pour passer les vacances à la côte 😀

Zig Zag Wanderer
Reply to  Krishna Gans
November 3, 2020 2:40 pm

In a related note, if you speak French properly, and hear a typical anglophone speak it, you can understand why the French hate hearing it. Even as an anglophone myself, I find it excruciating. The mouth is used in a completely different way, to the point where when I spoke English after 3 months without, I had a French accent!

Krishna Gans
Reply to  Zig Zag Wanderer
November 3, 2020 2:52 pm

As I came back of France after a year and met my parents, I couldn’t believe what I heard coming out of my mouth 😀
I needed a week to speak my original German without French background, from time to time I had still some fall-backs 😀
There are words in French ending in “if”, same word in German but “iv”
When writing in German as I usualy do, I have always to pay attention to remember ‘it’s German, “iv” ‘

Krishna Gans
Reply to  Zig Zag Wanderer
November 3, 2020 2:54 pm

Listen to “Les Nocturnes” at French RTL Radio, amazing 😀

Zig Zag Wanderer
Reply to  Krishna Gans
November 3, 2020 5:47 pm

I’ll do that, thanks. It could get my accent back for my (hopefully) trip next summer.

November 3, 2020 2:45 am

I guess this is as good as an explanation as any. A place to start. Though I don’t understand what practical application such knowledge would have.

Dodgy Geezer
November 3, 2020 2:46 am

My (simplistic) understanding of Vitamin D is that it is generated by the action of sunlight on our skin, and plays a part in supporting the chemistry of our immune systems.

Humans are therefore likely to have lower vitamin D levels over their local winter season. And human body forms which evolved for optimum capability in the tropics where seasons do not exist are particularly likely to have less capable immune systems during high-latitude winters. Which indeed seems to be the case.

Joel O’Bryan
Reply to  Dodgy Geezer
November 3, 2020 4:00 am

Evolutionary genetics has strong evidence of human skin coloration/pigmentation in a population evolves to balance vitamin D requirements with folate destruction via UV exposure.
While many have heard of the need for sunshine to produce Vitamin D, few people realize this comes with a downside on folate metabolism. UV destroys folate circulating in capillaries in the skin. If you get lots if sun, take a daily multi-B vitamin supplement. Women of child bearing age this is critical to maintain folate levels. Folate supplements are standard in prenatal nutrition advice during pregnancy.

Dodgy Geezer
Reply to  Joel O’Bryan
November 3, 2020 5:20 am

So Negros ought to develop a more Caucasian skin tone if they migrate to higher latitudes?

Reply to  Dodgy Geezer
November 3, 2020 7:38 am

Sort of. Not quite. If it weren’t for the effects of civilization they would be out-competed by white skinned people and die out.

If I understand correctly, most Europeans were dark skinned at the beginning of the Holocene. link

The dark skinned aboriginals of the arctic solved the problem by eating marine mammals and fatty fish which are rich in Vitamin D. link

More recently my dear Swedish mother solved the problem by feeding me lots of yummy cod liver oil. Bleah!

Dodgy Geezer
Reply to  commieBob
November 3, 2020 10:19 am

I suspect that, If we continue the movement from country to town which started in early Victorian times, we will all end up with a very pallid skin, akin to cave-dwelling animals…

Zig Zag Wanderer
Reply to  commieBob
November 3, 2020 2:45 pm

Dodgy, I can tell you, if you live in the tropics, when most English tourists visit, they look like fine white porcelain to us. Almost too hard to look at in direct sunshine they are so white.

Then they slather on sunscreen and sit in the midday sun. Mad dogs & Englishman!

Reply to  Joel O’Bryan
November 3, 2020 9:37 am

Thanks, Joel, interesting to know. I do take a B50 supplement.

Ron Long
November 3, 2020 2:50 am

There appears to me to be a fair amount of logic to their contention about UV energy and virus cycles. It will be interesting to see how we (southern hemisphere) follow this cycle as we are seven months into a lock-up-or-down, depending on your view. It appears a person can utilize sun screen as personal protection while the UV death rays are killing the airborne virus molecules, a win-win kind of a deal. I’m on my way to a therapy session, more commonly known as a round of golf. Cheers.

Bill In Oz
November 3, 2020 2:52 am

News from Australia : We’ve been in lockdown ith the borders closed to all except those going through two weeks quarantine. And uess what ? No flu’s or colds or other usual Wintery viral diseases. And death rates in each state ( except Victoria ) are lower than last year.

Ummmm ? I willing to accept that solar insolation has an impact. But I are very very sure that quarantine of all incoming travellers to Australia prevented the entry of many infectious diseases including Covid 19.

PS If you want to come & seek refuge here, it costs about $4000 for 2 weeks compulsory policed quarantine. But there is a huge queue ! 🙂

Reply to  Bill In Oz
November 3, 2020 3:55 am

Bill in Oz, I live in Qld where we have had practically no lockdown but closed borders including flights and ships. From the very start in late Feb. we have at all times been allowed to go out doors, swim at the beach, walk and run in the park taking in the sun and fresh air. For sometime restaurants and pubs were off limits inside but one could go and get takeaway to eat and takehome. Many shops were open such as supermarkets (Coles, Woolworths, IGA etc). Hardware shops were open so poeple at home could do renovations. The building industry was going ahead (of course required by unions). Mining and farming continued. The tourist industry has been hard hit. There has been practically no local transmission. Those tested having the virus has been nearly totally due to someone bringing in the virus either taken off ships, coming in from overseas, and people sneaking in from Melbourne or Sydney.
The sun plays a large part in Qld. having very few deaths. The whole thing could have been handled much better with for example more testing and giving certificates to those that test negative. Testing results should be give much quicker. My wife was tested at 4PM and she had the all clear at 9AM. Now there is a test giving a result in 15mins. In Taiwan the government gave everyone forehead temperature measuring which was used at the entrance to shops and buildings,. They had very few deaths.

Tom in Florida
Reply to  cementafriend
November 3, 2020 6:35 am

Testing negative only means you are negative at that point in time. It is not immunity and doesn’t mean that you will not catch the virus minutes later.

Reply to  Tom in Florida
November 3, 2020 6:59 am

That’s the reason I am not in favour of more testing. Simply wastage of money.
I also believe the vaccine will not be a cure as people develop the disease even they once had it.

Zig Zag Wanderer
Reply to  James
November 3, 2020 2:48 pm

You have proof of that, or just media stories?

Moderately Cross of East Anglia
November 3, 2020 2:52 am

The link between the Sun and some viral seasonality seems unequivocal, but may be only the tip of the Sunberg.
Back in 1958 a truly fascinating paper was published by Max Knoll in the Eranos yearbook “Man and Time”. The Eranos yearbook was a summary of the then annual meetings of a group of distinguished scholars mostly drawn form the psychological sciences, mythographers, historians, biological science and various other disciplines.

Max Knoll’s article was entitled “Transformation of Science in Our Age” and was a kind of pre-figuring of how we were just beginning to understand links between physical phenomena and human wellbeing at a deeper level. The article was a real standout in what is always a fascinating yearbook, but the real sting in the tail was an appendix “B.Some Astrobiological Phenomena” which looked briefly at the work by various specialists who had found correlations between the Sun and the rate of incidence of various diseases and mortality fluctuations.

A particular stunning feature is a page (no.295) of graphs based on the 27 day solar rotation. Graphs are shown for the monthly variation in death rates in Copenhagen, sunspot numbers, death rates from diseases of the nervous system and sense organs and mental disease, deaths from suicide, deaths from circulatory diseases and senility diseases, respiratory failure diseases, and all causes excluding homicides.

The astonishing thing is how entirely similar the plots are to each other and the 27 day sunspot and magnetic “character” over a solar month. ( It struck me that the graphs all look remarkably like the double peak of a heartbeat).

I know that you have to be very suspicious of spurious correlations, but the almost identical appearance of the plots looks very remarkable. I have no idea whether this paper has ever been examined by qualified people since or been totally discredited or even been looked at since. But if any of the correlations hold true either in the particular or generality then they must be of some importance, even if only in terms of medical planning. I certainly don’t feel qualified to pass any judgement on the validity of the paper, but it was prepared for a very distinguished audience which would quickly have ripped to shreds any sub-standard work.

(Yes, if you are wondering, I found it fascinating reading because I’m interested in antiquity and much of the Eranos yearbooks is about early history and humanity)

Edward Hanley
November 3, 2020 2:54 am

From the article: ” their theoretical model shows that both the prevalence and evolution of epidemics are strongly correlated with the amount of daily solar irradiation that hits a given location on the Earth at a given time of the year.”
I hate being “that guy,” but someone has to say it: mathematically modeling empirical data to discover a pattern does not take an idea from hypothesis to theory. I give them props for finding correlations, but correlation does not prove causation. And the hypothesis of UV weakening of viral dose has been around as long as the common cold.
That said, the authors also say, “…but the predictive power of the model depends critically (other than on the implementation of new restriction measures) on the exact UV-B/A lethal doses for the Covid-19 virus, which our collaboration is about to measure.” Ahah! Collecting data! THAT is how science takes an idea from hypothesis to theory. So they are scientists after all, and we can wait for their next report.
TLDR: Calling a hypothesis a theory distorts the process of science and harms the education of potential young scientists – children – who grow up with the common fallacy that imagining or stating an idea proves its reality.

robin townsend
Reply to  Edward Hanley
November 3, 2020 6:29 am

well said

Reply to  Edward Hanley
November 3, 2020 9:07 am

> Mathematically modeling empirical data to discover a pattern does not take an idea from hypothesis to theory.

I am sooo stealing that. Bravo. Very Richard Feynman.

November 3, 2020 4:00 am

ooooh the correlation im looking at?
is the ENSO meters wonderful big swing to the near -1.5

you little ripper(for aussie rains)

Krishna Gans
Reply to  ozspeaksup
November 3, 2020 7:07 am
Tom in Florida
November 3, 2020 4:20 am

I guess that humans spending more time confined indoors during winter has nothing to do with it.

Reply to  Tom in Florida
November 3, 2020 6:11 am

Tome in Florider
You are hereby banned from the internet for one week for destroying the nonsense study summarized here, with just one sentence. I was going to type the same thing, with about 500 more words, but you beat me to it.

Note that infections and hospitalizations increased in the Southern US states as the weather got hot last summer, and people stayed indoors for air conditioning a lot more. Especially older people who could not take the heat.

As the weather got colder in October, people in northern states spent more time indoors to stay warm, and they spread the infection faster than when they were spending more time outdoors in the summer.

An eight year old child could understand this. I’m sending an eight year old child to the study authors to explain it to them.

Vitamin D might be involved too. But many multiple vitamins and calcium pills and milk already contain Vitamin D. I found I was taking 3000 IU a day BEFORE the pandemic. Since I don’t get much sunlight because of sun burn issues, I immediately added a 5,000 IU a day D3. That’s real medical insurance. I have not caught COVID, even as five friends were infected. However, all the hair suddenly fell off the top of my head.

John F Hultquist
Reply to  Richard Greene
November 3, 2020 9:29 am

I live at 47° North Latitude with mostly clear sky. Summer sunlight is intense, winters are cold, and lots of wind.
I cover up in both winter and summer. Vitamin D from sunlight is small.

Our USA medical professionals have not advocated testing for Vit D because the benefits have not been shown in a manner that meets criteria.
That is not to say benefits are not known. This may change.
Anyway, my Physician Assistant thought taking a supplement of 2,500 units was fine. Going higher, she thought, ought to wait for a test. As yet, insurance is not likely going to cover that cost because . . .
– wait for it –
” … the benefits have not been shown in a manner that meets criteria.

November 3, 2020 4:30 am

The solar UV light that reaches the Earth must therefore have some disinfecting power…

It’s why they use UV in sewage treatment.

Reply to  fretslider
November 3, 2020 7:00 am

But not natural UV.

November 3, 2020 5:06 am

So much for the masks hand sanitiser social distancing and lockdowns. Trump is vindicated-
Either that or solar is pinching all the sunlight.

Bruce Cobb
November 3, 2020 5:23 am

Well, we know that viruses spread indoors, not outside, so the UV light would have to have its sterilizing effect indoors. Not very likely. If there was an effect, it would be very small. Not unlike the warming effect of man’s CO2.

November 3, 2020 5:34 am

It’s Vitamin D.

Read this 2006 article, “Epidemic Influenza and Vitamin D.” and the 2008 followup “On the Epidemiology of Influenza.”

This blog post addresses the epidemiology of the coronavirus and Vitamin D:

A C Osborn
Reply to  TedL
November 3, 2020 6:16 am

Spot on, great studies.

November 3, 2020 6:15 am

A contrary view is that the so-called seasonality of virus is in fact the effect of humans moving within their countries/communities at certain times of the year. Herd immunity is transient if enough people move from one herd to another. In the northern hemisphere, late August brings a large movement of new college and school entrants, there is a peak house purchase/rental, job movements peak etc. Its estimate up to 10% of the population changes its ‘herd’. This affects the immunity levels for a few weeks until it all settles down again. Hence ‘freshers flu’ , kids getting ill at new schools, older people getting admitted into hospitals from virus illnesses etc.
Nothing to do with weather, climate, the sun etc, its just movement of people.

Reply to  JimW
November 3, 2020 11:49 am

The “kissing disease” was what in my school days we called getting “mono” (mono-nucleosis). The jibe was that getting “mono” was a rite of passage for freshman gone off to attend university because in those days that was when they took advantage of permissive social saliva swapping.

Dr. Deanster
November 3, 2020 7:01 am

One of these days, the indoctrinated in the Academia and Medical Sciences will embrace that the difference is not the virus, it is the PATIENT.

The virus, be it the flu, cold, corona, rhino, etc, never really changes throughout the year. What changes is the patient’s susceptibility to it. Our immune systems strengthen in the Spring and Summer and weaken in the Fall and Winter. Take a look at the “Deaths” plot for the US for COVID19, the spike in deaths was back in March-April. It fell after that, and if not for all the testing and hyperventilating over it, the numbers would probably be lower than reported. The Flu is well documented to be seasonal. Only Rhinovirus seems to buck the trend a little, but even it greatly diminishes during the Summer.

COVID would be a non-issue if not for the fact that the US is stocked full of unhealthy, entitlement minded potential Darwin Award recipients who’s mentality is that it is Medical Science’s job to save them from their unhealthy life styles. A healthy immune system may not prevent you from being in infected, but it will usually prevent you from dying.

Then answer, IMO as a Human Health Risk Assessor, is .. lose the weight, clean up your diet, exercise, take your vitamins and minerals (specifically, A, B12, C, D, and E, and Selenium, Zinc and Magnesium), get your diabetes and hypertension under control, … and your risk of dying from COVID becomes extremely low.

Reply to  Dr. Deanster
November 3, 2020 8:15 am

I’d add B1 (thiamine) to that vitamin list, but your comment is spot on. The news screams every day how America has the highest Covid death rate in the world, but doesn’t mention much that we are also the fattest people around, worst physical shape, eat far more poor food filled with chemicals, artificial ingredients, HFCS, etc, etc. And having such a great medical system has allowed many more of us to live, perhaps in poor physical condition, to a ripe old age. And we’ve had the “slather yourself in SPF 50 before even looking out the window” solar phobia for at least 30 years now, so it’s no surprise we’re all D deficient.

Look at Vietnam. A very young population, a largely outdoors culture, tropical climate, almost no obesity, everyone is saturated with antimalarial meds, antiparasitics too probably … yet with a population 1/3 of USA in 1/29 the land area, their total Covid death count is something like 35 at this point.

Reply to  Drew458
November 3, 2020 10:49 am

I think to be fair though, it’s quite hard to extrapolate the effect of general health of the population from the available (horrible) data without diminishing/destroying the idea that the USA is the worst.

In addition to the “normal” epidemiology, whatever that is, there was something quite peculiar that occurred in the northeast states. The mortality there was incredibly high, lots of dense population of highly vulnerable older people, and I also suspect improper early procedures when it came to use of ventilators.

If you remove that from our data, or even normalize it to mortality rates the rest of the country has experienced, we look pretty average.

Reply to  Drew458
November 3, 2020 7:26 pm

Drew458 November 3, 2020 at 8:15 am wrote:

“Look at Vietnam. ..their Covid death count is somethin like 35…”

in the paper:

Vitamin D in COVID – 19: Dousing the fire or averting the storm? A
perspective from the Asia-Pacific

There you’ll note that only five countries in the world are shown as having D blood levels above 30 ng/ml. The map is pretty small, but I believe the four shown in Asia appear to be Malaysia, Thailand, Taiwan, and VIETNAM . The only one shown in the other inhabited continents is SWEDEN!

Coincidence? Sweden is particularly remarkable, because it accepted a fairly large number of Syrian and other middle eastern refugies in recent years, which would tend to bring their average D levels down.

Reply to  Dr. Deanster
November 3, 2020 9:44 am

“What changes is the patient’s susceptibility to it.”
“lose the weight, clean up your diet, exercise, take your vitamins and minerals”

Solid gold. Why are none of the authorities saying this? Not even Sweden?
Best practices in summer include going to the beach, yet that was banned in so many places.

November 3, 2020 7:02 am

Bring on herd immunity and stop these country-destroying lockdowns now! From the BMJ: Covid-19: T cell response lasts for at least six months after infection, study shows.

Don Thompson
November 3, 2020 8:55 am

UV-C is effective, and adding UV lights to HVAC systems should become standard, especially for congregate settings. Also, vitamin D, Zinc and Floutoconase (Flonase) should be used for those who don’t have contraindications.

November 3, 2020 9:39 am

Please bare with me on this because it’s very important to what I say later about COVID-19 and the use of Far UVC on Respiratory Viruses.

In March of 2019 I had a Heart Attack brought on by 2 decades of type 2 diabetes. My Cardiologist warned me I was High Risk about Respiratory Viruses and Respiratory Bacterial Infections that could literally kill me and I needed to take extra precautions. I was prescribed 50 mcg Vitamin D3 twice a day. Along with Brilinta blood thinner, a 81 mg Aspirin and Atorvastatin calcium.

I have been studying about Respiratory Pathogens since April of 2019 and logged well over 400 hours of research since then by reading actual studies and history of these Pathogens. When SARS-CoV-2 came to the U.S. in February of 2020 this added to my concerns and most of those hours of research have been since then. I was OSHA Certified in 1998 and months of studying of all forms of PPE was required to pass the exams. I have had Chronic Bronchitis all my adult life. I have worked in many fields where PPE was required and I have numerous hobbies where PPE are required. Before I got my OSHA Certification a Respiratory Specialist told me I have been slowly killing myself by creating Hypoxia from decades of wearing PPE that has lowered my Blood Oxygenation and reduced my Lung Capasity. She told me this by itself most likely contributed to my type 2 Diabetes and being overweight (376 lbs at that time) also being a cause of Hypoxia Conditions.

Every Health Conditions I mentioned makes me Extremely High Risk for Respiratory Pathogens. And my wife is also Extremely High Risk too. Just so you know why my educating myself was important.

My OSHA Certification was never used because of my health and would have required my wearing of more PPE wherever I had to do inspections. None of the Medical Grades of “Masks” are designed to “Reduce the Spreading of Viruses” and many studies say that under Controlled Conditions the Reduction of Pathogens was “Insignificant” in comparison to those whom wore nothing to those that wore “Masks” that were professionally Fitted to the other’s. “Insignificant” ranging from 2% to 4% Reductions depending on the studies. When you take that being under Controlled Conditions and then Governments making Mandates for the General Population that are Untrained in their use, that even if EVERYONE wore Professional Grades of “Masks” that would Insignificantly Reduce the Spreading. But they’re ideologies are that even an “Insignificant Reduction” becomes “Significant Reductions” in populations of Millions of people.

Now about Ultraviolet Radiation being able to Destroy the RNA of Respiratory Pathogens rendering them Non-Contagious is well documented. Once their outer RNA Protiens are destroyed they can’t enter into other cells to Reproduce. Ultraviolet Radiation destroys those RNA Protiens but UVA and UVB are too big of a Particle Size to enter into those RNA. And both UVA and UVB and UVC larger than 257 μm are known to cause Cancer and Retinal Deterioration. Our Atmosphere effectively destroys UVC in the Stratosphere and Ionosphere before it can reach the Troposphere…except maybe some that comes through Ozone Holes. Governments have not given Reccomendations for Ultraviolet Light because of their Carcinogenic and Retinal Deterioration effects against Viruses. But several newer studies with Far UVC under 222 μm have proven to Destroy Viruses RNA and is too small to penetrate into below the Dead Skin Layer to cause Cancer and any Retinal Damage other than feeling like you have Sand in your eyes if you’re looking at the Far UVC Light Source for very long. Since Visible Lights are Rays emitted from a source they can be reflected off of materials and penetrate materials to various degrees. But Far UVC can only be created artificially using High Grade Quartz Glass as normal Silica Glass used in Windows blocks Ultraviolet Radiation and the newer the Window Panes the higher the UV Protection that have for Energy Efficiency. So wearing Sunglasses and especially those Blue Blocker types when around Far UVC is how I keep from getting that “Sand in the Eyes” feeling. Medical Facilities have used Multigermacidal Ultraviolet Lights as Disinfectants for many years to treat rooms, hallways and to sterilize medical equipment and instruments. Many Asian Countries have been putting Far UVC Lights in all their Public Transportation and Facilities and Medical Facilities since this COVID-19 Pandemic. You’re more likely to get Cancer or Retinal Damage just going outside for awhile than from Far UVC Lights on constantly. But the “downside” is that Far UVC doesn’t penetrate things like Dust Particles where Aerosols of Mucous Containing Viruses can latch onto them. It cannot penetrate into small nooks and crevices or underneath anything the Light Rays are not reaching. But in every building these Far UVC Lights can be strategically placed to Destroy Viruses in Aerosols and on Surfaces…with great effect of Reducing them and used both daylight and night. Just a half a second was found to Destroy the RNA of SARS-CoV-2 under Far UVC by one study I read.

As for this “Seasonal Spreading” you can literally follow how outbreaks increase and decrease by the Weather Changes. But it’s not because of the Solar Activity Radiation on these Pathogens. It’s because the Population goes inside more whenever these Weather Changes occur and the studies in Asia showed how Recirculated Air Conditioning was where the majority of their population cases and death’s occurred, where the districts that were poorer had fewer to no cases and death’s as their buildings had more open airflow with shutters and not window panes and the population lived more outside than inside. The Pandemic hit the U.S. Northeast and West Coast first whenever it was Colder and Hotter. As cases and death’s declined there it increased in the Southern States as it got hotter and more people moved Inside. As we are entering Autumn the cases and death’s are increasing because more of the population is going inside longer than being Outside. Airborne Viruses created by the Wearing of Masks makes Large Globs of Infected Mucous into Tiny Aerosols that linger for days INSIDE Air Controlled Buildings. Where Masks are designed to retain the Larger than their Pore Size Particles. Mucous is a Fluid that breaks apart under the pressure of normal breathing and those larger particles become smaller particles that becomes Airborne. This is simple science. All “Masks” are rated using Preconditioned 80% Humidity for 30 minutes before being professionally put into a Dummy. Then an exact measure of Dry Sodium Chloride of a specific Mesh is directed onto these “Masks” where a specific Vacuum is used to draw air through the Mask. Any fool understands that Salt hitting Moisture cakes up on the Material. The amount that goes through the Pores is measured to obtain their Rating.

Being Outside not only gives us Vitamin D through our skin but also through our Eyes. Vitamin D Deficiency was the first discoveries found in Europe to whomever was getting the sickest to those Asymptomatic. Living Inside reduces the Ultraviolet Radiation that creates Vitamin D the population is getting far less of. While living inside where these Aerosols can linger for days. And those Aerosols are small enough to contain hundreds of any Viruses in Aerosols Small enough to go right through the Pores of Professional Masks…as people are wearing Cloth Face Coverings. That their “Lifestyles” are what is causing these Pathogens to become Pandemic.

Allen Stoner
November 3, 2020 10:02 am

This is really something that was never really studied before? I guess it is one of those things that is so well known that everyone else also thought this was a known quantity. It could also be that the changes in solar irradiance causes reductions in Vitamin D.

Dr. Deanster
Reply to  Allen Stoner
November 3, 2020 10:18 am

Allen …. that is not a “could also be” … it is a proven fact and the demographics of the deaths bore it out here in the States.

Deaths increase with latitude
Deaths increase in African Americans
Deaths increase in the elderly (who are more prone to be vit D def.)
Deaths increase in obese people …. a known risk factor for Vit D def.
Deaths increase in people with medical conditions like diabetes and heart disease, also associated with vit d def.

If our STUPID media would have replaced a PSA on Vit D for every time they tried to blame Trump for the deaths in the States, our death rate due to COVID19 would be statistically non-existent.

Reply to  Dr. Deanster
November 3, 2020 11:40 am

Has anyone anywhere ever seen a PSA for Vitamin D?

Dr. Deanster
Reply to  Toto
November 3, 2020 7:25 pm

I did see a story on Faux News about the possible benefits of Vit D. Does that count?

Bob Weber
November 3, 2020 3:52 pm

I agree with the authors that the sun has a role in disease, but what is actually happening?

Many of the historical flu outbreaks happened during solar minimums like in 2009, 1976, and 1917 which appear to follow a similar pattern, suggesting a common mechanism that may be unrelated or tangentially related to viruses. The mechanism is low TSI driven lower tropical evaporation and clearer skies leading to higher UV Index and associated high heat index. I specifically predicted in my 2018 AGU poster for this time period the SW US would experience dry heat conditions, as evidenced by the growth in drought this year out west.

It is well known that ultraviolet (UV) light is able to deactivate viruses and bacteria of many different kinds.

High UV Index (UVI) in the southern US, Brazil, and India etal would’ve then deactivated CV19?

If so then why were most of the CV19 attributed ‘cases’ and deaths in the US south this summer when UVI was 2-5 SD above average, and when UVI was 10 or higher in Phoenix?

Because high UVI leads to high heat index and heat-related illnesses, which I think was the primary ‘CV19’ driver of June-Sep illnesses/deaths until cold weather cold/flu/pnuemonia responses started in October.

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The last link was used with my abstract on July 31, to be updated for an AGU presentation in Dec including a more comprehensive summary of 2020, linking weather and CV19 after the initial outbreak March-May.

If I’m right it means ‘tests’ aren’t specific enough for viruses as PCR test inventor Kary Mullins claimed.

November 4, 2020 1:38 pm

What about bird virus transfer?

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