Will a long, hot summer stop the spread of COVID-19? We haven’t really warmed up to the idea.
Who is propagating the myth?
Back in February, U.S. President Donald Trump made the following comment about SARS-CoV-2 (COVID-19):
“Now, the virus that we’re talking about having to do — you know, a lot of people think that goes away in April with the heat — as the heat comes in. Typically, that will go away in April.”1
This eloquent musing got people wondering if SARS-CoV-2 will go away with warmer temperatures. Others have been suggesting that maybe SARS-CoV-2 will be seasonal like the influenza virus, which causes the flu. In fact, temperature and humidity contribute to the survival of the human influenza virus – it transmits most readily in cold and dry conditions.2 This has led many to ask: Will these same factors affect the survival of SARS-CoV-2?
Where did this myth come from?
There has been some evidence from different research groups suggesting that the transmission of SARS-CoV-2 is less efficient in warmer temperatures. For example, a recent laboratory study by Chin et al. found that SARS-CoV-2 was stable at 4°C but that it was sensitive to heat, with higher temperatures leading to shorter times for virus inactivation.3
Another study looking at SARS-CoV-2 transmission in China found that increased temperature and humidity led to a decrease in daily confirmed cases; however, these were not consistent throughout all geographic regions in Mainland China which were part of the study.4
It is also important to recognize that the number of studies available on the impact of temperature and climate on SARS-CoV-2 are still limited, and some have yet to be peer-reviewed. More information is likely to emerge with further scientific investigations.
Why is it wrong?
If the research may seem to support a relationship between warm weather and reduced transmission of SARS-CoV-2, why can’t we assume that there will be slowed transmission of SARS-CoV-2 when warmer temperatures come our way?
Firstly, it can be hard to generalize findings coming from a lab to the real-world, because laboratory conditions are different than real-world conditions. This concern was voiced by the National Academies of Sciences, Engineering, and Medicine of the United States, a prestigious scientific panel, in their report to the White House on the impact of temperature and humidity on the novel coronavirus.5 One of the problems with lab studies is that a virus that is grown in a lab may have different survival properties than the same virus coming from a naturally-infected human.5 However, certain lab studies may be more informative than others. For example, studies that look at how a lab-grown virus acts when it is released into the environment via human fluids (e.g. saliva or mucous) may be more applicable to the real world compared with studies that look at virus release into the environment via an artificial substance from a lab.5
Further, even though studies from China have shown a relationship between the number of cases and temperature and humidity,4 countries currently experiencing a “summer climate,” such as Australia or Iran, are still experiencing rapid spread of the virus,5 which suggests that warm temperatures are unlikely to completely halt the spread of this virus. Also, there are many other factors that influence the number of cases in a given geographical area other than temperature and humidity, such as access to and quality of public health, health care systems, per capita income, and patterns of human behavior.5 It is hard to generalize something that occurred in another part of the world to our own current situation.
The consensus of the report delivered by the National Academies of Sciences, Engineering, and Medicine is that even if temperature and humidity do reduce the transmission of the virus, the effect will not be as obvious as with other respiratory viruses.5
Why might that be?
Let’s compare SARS-CoV-2 to influenza for example. As warmer temperatures and humidity come about, it is more difficult for the influenza virus to spread between people because of its inherent survival properties. However, at the same time, there is already some immunity within communities from either previous exposure to the virus (i.e. already having or being exposed to the flu that season) or getting the flu vaccine.6 This further helps stop the spread! However, in the case of SARS-CoV-2, we have never encountered this virus before. Therefore, there is a lack of immunity to SARS-CoV-2 all across the world, so it is still likely to spread efficiently between people even if warmer temperatures theoretically impact its survival.
What are the ramifications of our misunderstanding?
Although some research may show that higher temperatures and humidity levels can lead to reduced survival of the novel coronavirus, there are many other factors affecting the transmission rate of this virus. As warmer temperatures come with spring, it is important that we continue to employ physical distancing measures, stay home whenever possible, and continue to wash our hands and practice good overall hygiene. So, make sure your mask/hand sanitizer accessory design is fashionably acceptable for multiple seasons. Nordic prints can only get us so far – it looks like we may need to bust out the florals and/or the classic summer citrus palette. While we can hope warm weather will help slow transmission rates, we cannot operate under the assumption this will be the case.
BUST OR NO BUST:
Myth: Warm weather and humidity is going to stop the spread of SARS-CoV-2 (COVID-19).
Results: Bust. Myth-meter 40/100 truthfulness.
Written by Christina Blagojevic
1. Remarks by President Trump at the White House Business Session with our Nation’s Governors. The White House (2020). Available from: https://www.whitehouse.gov/briefings-statements/remarks-president-trump-white-house-business-session-nations-governors/
2. Lowen AC, Steel J. Roles of humidity and temperature in shaping influenza seasonality. Journal of virology (2014). doi: 10.1128/JVI.03544-13
3. Chen YH, Chen YC, Liu CS, Hsieh MC. The different effects of atorvastatin and pravastatin on cell death and PARP activity in pancreatic NIT-1 cells. Journal of diabetes research, 2016 (2016). doi: 10.1155/2016/1828071
4. Qi H, Xiao S, Shi R, Ward MP, Chen Y, Tu W, Su Q, Wang W, Wang X, Zhang Z. COVID-19 transmission in Mainland China is associated with temperature and humidity: a time-series analysis. medRxiv (2020). doi: 10.1101/2020.03.30.20044099
5. National Academies of Sciences, Engineering, and Medicine. 2020. 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). Washington, DC: The National Academies Press. doi: 10.17226/25771
6. CDC. Seasonal Flu vs. Pandemic Flu. Centers for Disease Control and Prevention (2019). Available from: https://www.cdc.gov/flu/pandemic-resources/basics/about.html