Will the Pandemic get Better with Warm Weather?

There is a widespread belief that warmer weather in the summertime will lower the number of Covid-19 cases. The reason is that the warm sun and humidity will kill the SARS-CoV-2 virus. The SARS-CoV-2 causes Covid-19 disease.

This is what the National Academy of Sciences, Engineering, and Medicine report tried to answer. The paper is called Rapid Expert Consultation on SARS-CoV-2 Survival in Relation to Temperature and Humidity and Potential for Seasonality for the COVID-19 Pandemic (April 7, 2020).

Inside the report, the scientists looked at the different experimental studies and natural history studies about epidemics to answer that question.

Experimental Data

In an experiment that was discussed in this article, How Long Can the Covid-19 Virus Survive in Common Surfaces?, Chin and others found out that viruses can survive for 7 days at 22°C or 71.6°F and only becomes undetected at 2 weeks.

The SARS-CoV-2 are completely gone after being exposed to 30 minutes at 56ºC (132.8°F) or after 5 minutes at 70ºC or 158°F. 

In another experiment at Tulane University, an aerosol with 2-micron particles were suspended in a rotating drum at an ambient temperature of ~23ºC (73.4°F) and ~50% humidity.

That means the SARS-CoV-2 has a longer half-life under these conditions than the influenza virus, SARS-CoV-1, monkeypox virus, and Mycobacterium tuberculosis.

Existing Experimental Data have Limitations

The report listed some caution about applying lab data to real-world uses. The first is that viruses that are grown in tissue culture (TC) media may have different survival properties than from naturally infected humans.

It would be better if the studied viruses came from human body fluids like saliva, respiratory (including nasal) mucus and lower respiratory tract airway secretions, urine, blood, and stool. 

Second is the issue of humidity. Laboratories often fail or are unable to maintain or vary the moisture in their study environment. The human respiratory tract is about 95% humidity and more protective of infection. Indoor relative humidity in wintertime in temperate regions is usually 20-40%, a range that is more favorable for virus survival.

Third, the SARS-CoV-2 virus may have different strains with different survival properties in varied temperatures and humidity conditions. That is why different viruses isolated from early and late in the pandemic, and from different geographic regions, should be studied and compared.

No Clear Pattern about Warm Weather and Previous Pandemics

At this time, published studies have produced conflicting results about seasonal effects to produce conclusions. There is some evidence that suggests that the SARS-CoV-2 virus may spread less efficiently in higher temperatures and humidity. However, because of the lack of herd immunity globally, that may not be a guarantee.

The other coronaviruses causing severe human illness, like the SARS-CoV and MERS-CoV, have not shown any pattern of seasonality.

Patterns of Covid-19 spread with regards to temperature and humidity changes have not been consistent in showing a decrease in the transmission with warmer temperatures. This suggests that many other factors contribute to disease spread.

Iran and Australia have “summer” weather right now and have 70,029, and 6,303 cases, respectively. The Philippines had an average temperature of 32.7°C  (90.9ºF) in March 2020. It has a total of 4,428 cases.

In the past 250 years, 10 influenza pandemics have happened. Two started in the northern hemisphere during the winter, three in the spring, two in the summer and three in the fall.

All of them had a peak second wave six months after the start of the pandemic regardless of what season they started.

The National Academy report concludes that more studies are needed to shed light on the effects of climate on transmission.

My Take: Don’t expect Less transmission in Warmer Weather

Most people prefer to be in a comfortable and relaxed environment. No one wants to be sweating all day, whether they are at home, inside a vehicle, working, studying, or in a sports arena. Nobody wants to eat in a hot restaurant.

That is why air-conditioners are turned on.

In developing countries, malls and movie houses are full during summertime.

According to Consumer Reports, the ideal settings for air-conditioners for comfort are 25ºC or 78° F. Going back at the temperature studies that are highlighted above,  the SARS-CoV-2 virus can survive for 7 days at 22°C or 71.6°F and only becomes undetectable at 14 days.

Granted that there is a 3 Centigrade degree difference between 22 and 25, we can safely assume that the Covid-19 virus can survive for several days in an airconditioned environment.

Any effect of warmer temperatures and higher humidity on the decrease of the spread of the virus outside the environment can be negated by the human preference to be in a cooler environment.

In the absence of clear cut information about the effect of warm weather on the current pandemic. We have to rely on what has proven to be effective.

Make Infection Control a Good Habit

Vaccines for Covid-19 are months away. No definite medicines are present, although many are undergoing clinical trials.

The Centers for Disease Control has issued guidelines for proper hand-washing, social distancing, and mask-wearing. 

All have proven effective in slowing the spread of the pandemic in China, South Korea, Italy, and Spain.

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Don’t Get Sick!

Related readings:

1. The Complete COVID-19 Articles

2. The Asymptomatic and Symptomatic Covid-19 are Equally Infectious

3. Physician Deaths from Covid-19

4. Can Talking Spread Viruses?

5. Why Scheduled Surgery Has to Wait in Covid-19

6. SARS-CoV-2 Contamination in the Hospital Setting

7. How Long Can the Covid-19 Virus Survive in Common Surfaces?

8. Zinc Deficiency Impairs the Immune System

9. Vitamin C and COVID-19

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