Will Summer Sunshine Suppress Coronavirus Pandemic?

Preliminary results of a US Government study reveal that the sunlight quickly destroys COVID19, the novel coronavirus. The study found that the risk of “transmission from surfaces outdoors is lower during daylight” and under higher temperature and humidity conditions, according to Yahoo News. This latest work reinforces the conclusions of "Will Coronavirus Pandemic Diminish by Summer?", a recent paper written jointly by Pakistani and Indian researchers at Massachusetts Institute of Technology. Ultraviolet (UV) light, a component of sunlight, has long been known to be an effective disinfectant.

Homeland Security Study: 

The study by US Department of Homeland Security scientists concludes that “sunlight destroys the virus quickly” but it also warns that enclosed areas with low humidity, such as airplane cabins, “may require additional care to minimize risk of transmission. ”Simulated sunlight “rapidly killed the virus in aerosols,” the study says, while without that treatment, “no significant loss of virus was detected in 60 minutes. ”While the DHS describes the results as preliminary, they may eventually make their way into specific recommendations. “Outdoor daytime environments are lower risk for transmission,” the briefing states.

Dr. Qasim Bukhari's Work: 

Dr. Qasim Bukhari, a Pakistani-American scientist at MIT,  told Yahoo News that since he and his colleagues published that analysis, the numbers on the coronavirus’s spread continue to support their contention. “They are doing a lot of tests now in India. Also, when you look at the numbers in Pakistan it’s the same. There are more than 5,000 cases in Pakistan right now,” he said. “But the increase is not as rapid as you see in other countries.”

Last month I followed up with Dr. Qasim Bukhari, a fellow NED University alumnus from Karachi, about his findings. Here's a brief Question/Answer version of the email exchange I had with Dr. Bukhari:

 RH: My understanding from the data I have seen from various sources is that the coronavirus transmission rates decline but do not necessarily go to zero in hot and humid weather. And the reason is that the fatty outer layer of the virus has trouble in heat and humidity. Is that accurate?

QB: That would be almost accurate. The only thing we don't know so far is, how much decline in growth rate we are talking about. It is definitely non-zero. The underlying reasons may be many or either of many. One reason could be the fatty outer layer reason that you mentioned. Other reason could be the antibacterial nature of sunlight, another reason could be low indirect transmission (through air) in high humidity.

"There is indeed evidence that weather plays a role, but in no way we are suggesting that this role alone would be so decisive as to completely halt the spread of COVID. And anyway, the affect of this weather would only be relevant in humid hot countries. Please do share, but please use the right words that properly communicate that it is incredibly important to take precautions and quarantine measures even in the most humid hot regions, as the spread would keep on going without that, we have evidence from Singapore, Malaysia and Indonesia of this."

Over 90% of Coronavirus Cases So Far in Red Zone. Source: Dr. Qasim Bukhari and Dr. Yusuf Jamil 

Wang, Weifeng, Beihang and Ke Tang: 

There is similar work that has recently been published by a Chinese research team that included Jingyuan Wang, Kai Feng, Weifeng Lv of Beihang University, and Ke Tang from Tsinghua University. They studied 100 different Chinese cities that each reported more than 40 cases of COVID-19 from Jan. 21 to 23, 2020.

“In the early dates of the outbreaks, countries with relatively lower air temperature and lower humidity (e.g. Korea, Japan and Iran) saw severe outbreaks than warmer and more humid countries (e.g. Singapore, Malaysia and Thailand) do," the researchers wrote.

COVID-16 Transmission Rates Vs Temperature and Humidity

Here's an excerpt from the abstract published by the team:

"After estimating the serial interval of COVID-19 from 105 pairs of the virus carrier and the infected, we calculate the daily effective reproductive number, R, for each of all 100 Chinese cities with more than 40 cases. Using the daily R values from January 21 to 23, 2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities, high temperature and high relative humidity significantly reduce the transmission of COVID-19, respectively, even after controlling for population density and GDP per capita of cities. One degree Celsius increase in temperature and one percent increase in relative humidity lower R by 0.0383 and 0.0224, respectively. This result is consistent with the fact that the high temperature and high humidity significantly reduce the transmission of influenza. It indicates that the arrival of summer and rainy season in the northern hemisphere can effectively reduce the transmission of the COVID-19."

Some experts are pointing to the increased amount of UV rays from the sun the Northern Hemisphere will be subject to this time of year as a factor that could slow the virus, according to a story in AccuWeather.

Dr. Anthony Fauci On Effect of Weather:

Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases (NIAID) who also serves on the White House coronavirus task force, has acknowledged that a change of season might affect COVID transmission rates.

Here's what he said at a recent White House briefing: “I think it (weather) very well might. And the reason I say that is that what we’re starting to see now in the Southern Hemisphere, in southern Africa and in the southern hemisphere countries, is that we’re having cases that are appearing as they go into their winter season. And if, in fact, they have a substantial outbreak, it will be inevitable that we need to be prepared, that we’ll get a cycle around the second time.”


A US Government study has found that the sunlight quickly destroys the coronavirus. Ultraviolet (UV) light, a component of sunlight, has long been known to be an effective disinfectant.  Mainstream US and Indian media have also widely covered a recent MIT paper on the effects of heat and humidity on coronavirus transmission. Dr. Qasim Bukhari, the lead author and alumnus of NED University located in Karachi, Pakistan, has shared data showing that 90% of the coronavirus cases so far have occurred  in a regions with absolute humidity between 4 and 10 grams per cubic meter. Recent Chinese research is also showing that hot and humid weather may significantly slow down transmission of coronavirus or COVID-19. An increase of just one degree Celsius and 1% relative humidity increase substantially lower the (Covid-19  or 2019-nCoV) virus’s transmission, says a study published on March 10, 2020 by Chinese researchers. One possible reason is that the fatty outer layer of the virus has trouble surviving in high heat and humidity. The virus disintegrates when the fatty outer cover is gone in a way similar to how the soap and hot water destroy it. This may explain why there appear to be relatively few reports of local COVID-19 transmissions in places like Pakistan. Most of the known coronavirus cases in Pakistan appear to be those of the people who have come into the country from cold, dry places like northern Iran where the pandemic is raging. The rate of local transmission in Pakistan is not zero but relatively low. Dr. Bukhari says that "there is indeed evidence that weather plays a role, but in no way we are suggesting that this role alone would be so decisive as to completely halt the spread of COVID."

Related Links:


Riaz Haq said…
Excepts of Wall Street Journal Story Why Youthful, Conservative Pakistan Is a Coronavirus Bright Spot

Two months ago, Pakistan was drawing unfavorable Covid-19 comparisons with Brazil


"Major hospitals report beds are freeing up in previously overflowing coronavirus wards, even in Pakistan’s biggest and hardest-hit city, Karachi," the Wall Street Journal said in a report from Islamabad. "The tally of patients on ventilators has halved over the past month," it adds.

"This is all happening as Pakistan’s neighbours to the east and west — India and Iran — are still reporting that infection rates are climbing steadily," the Journal said.

Even more surprising, the report added, was how the progress in Pakistan — where coronavirus was spreading out of control some two months ago — came after Prime Minister Imran Khan resisted the World Health Organization's (WHO) advice, declaring in May that lockdowns are too costly for the poor and reopening the economy.

"We charted the tough course between a strict lockdown and completely opening up," Dr Faisal Sultan, an infectious diseases physician brought in by PM Imran Khan as his adviser for COVID-19.

The report about Pakistan’s success comes when even the US — a superpower with enormous resources at its disposal — struggles to control the pandemic, with 4.7 million cases and 157,000 deaths.

PM Imran started wearing a mask in public

Pakistani health officials have not declared a win, the report said, adding they worry that progress could be undone, particularly with the current Eid-ul-Azha holiday and the upcoming Muharram, both of which traditionally attract public gatherings across the country.

Relatively low testing levels in Pakistan have also raised questions about the scale of the decline, the Journal noted, but quoted medical experts as saying that the turnaround trend is clear. Tellingly, the proportion of tests coming back positive has more than halved, it said, citing official figures.

Pakistan locked its economy down in March, early on in its outbreak, which kept the virus from spreading widely while the population stayed home, the WSJ stated. However, after the restrictions were lifted in May, many Pakistanis celebrated the end of the fasting month of Ramazan with shopping sprees and visits to family, unleashing a burst of infections.

The rapid spread jolted people into changing their behavior, with more mask-wearing, hand-washing, and maintaining social distance, Dr Sultan was cited as saying. The preventive messages increased from the government and public service campaigns.

The prime minister also started wearing a mask in public, the report highlighted


Just 4% of Pakistan’s population is over 65 — compared with 16% in the US and 23% in Italy, according to United Nations data. The average age in Pakistan is 22, more than a decade younger than Brazil, and 25 years younger than Italy, noting also that there are no bars and nightclubs.

There are also no institutionalised homes for the elderly, sites of deadly outbreaks elsewhere. Women tend not to go out of the home to work, meaning the workforce is overwhelmingly made up of men who are mostly young, it was pointed out.

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