Though it is reassuring to think that the pandemic will slow naturally because of warmer weather, this hope is largely based on comparisons with seasonal viruses. It is unlikely that the coronavirus, in its first season will be strongly seasonal.

The speed at which countries manage to get over the peak in cases will be determined by how well and how fast citizens can implement the advice on social distancing and staying at home to break transmission. This action is more likely to determine when the pandemic will slow than the weather.

This false hope was first amplified on social media after a February 10th press conference, in the White House where it was suggested that the coronavirus might simply die out as the weather gets warmer.

There are early studies in non-peer reviewed pre-print journals that have quickly sought to collect data or model the infectivity of this virus in different regions and populations. Though promising, none provide high level evidence yet to overturn the idea that it is citizens behaviour supported by their governments actions that will stem the tide of this epidemic later in the year.

Where did the story come from?

Multiple social media sources accounts and commentators have amplified this story in both positive and negative ways.

 

What is the basis for the claim?

The idea that warmer weather may stem the spread of the disease comes largely from a comparison with the flu. As a respiratory illness, COVID-19 is similar to the flu. Both viruses spread through respiratory secretions and contaminated surfaces. Both illnesses can cause typically mild respiratory disease that in some cases develops into life-threatening pneumonia. But the chain of transmission can be different for a new virus and we don’t yet know enough about the virus SARS-CoV-2.

A Massachusetts Institute of Technology review published on the 19th of March used data compiled by John Hopkins University to investigate the rates of transmissions with coronavirus in regions of the world where temperatures range between 3 and 13°C. on that date 5% cases were observed in countries where temperatures were above 18°C.

These authors emphasis that the proper social distancing, quarantine and isolation measures will be required to effectively reduce the transmission of SARS-CoV-2 (the virus) and protect those people who are at risk of more serious COVID-19 (the disease).

Ecological studies and modelling of the spread of SARS-CoV-2 in different climates data have recently been published. So far many have not gone through a peer reviewed process and so provide low-level evidence of a link to weather or temperature. The first study models monthly variation in climate and likely transmission of the virus throughout the year. The authors found that the coronavirus displays a preference for cool and dry conditions over hot and humid ones.

The authors of another study conducted in China calculate the daily reproductive number (R0), a measure of how many people are infected by each primary case across different Chinese cities. In cites with more than 40 cases an associaton between high temperature and humidity with lower transmission (R0) was found after controlling for the population density.

Early research like this will need to be repeated in more countries before anyone can be confident of links between transmission and climate.

 

What do trusted sources say?

The World Health Organization noted that the COVID-19 virus can be transmitted in all areas, including those with hot and humid weather.

The Centres for Disease Control and Prevention mention that it is not currently known whether temperature and warm weather will have an impact on the spread of COVID-19.

 

Citation

  1. MIT Technology Review. Warmer weather could slow down the spread of the coronavirus. Karen Hao. Available at: https://www.technologyreview.com/s/615381/coronavirus-spread-could-slow-with-warmer-weather/ (Accessed March 20, 2020)

 

Reading list

1.     Center for Disease Control. Coronavirus Disease 2019 (COVID-19). Frequently Asked Questions. Available at: https://www.cdc.gov/coronavirus/2019-ncov/faq.html (Accessed March 20, 2020)

2.     Wang J, Tang K, Feng K, et al. High temperature and high humidity reduce the transmission of COVID-19. March 9 2020 Available at: https://arxiv.org/ftp/arxiv/papers/2003/2003.05003.pdf (Accessed March 20, 2020)

3.     Arauko M and Naimi B. Spread of SARS-CoV-2 Coronavirus likely to be constrained by climate. Available at: https://www.medrxiv.org/content/10.1101/2020.03.12.20034728v1 (Accessed March 20, 2020)

4.     World Health Organization. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/myth-busters (Accessed March 20, 2020)