Can high temperatures stop the expansion of the coronavirus?

By Jeremy Rossman, University of Kent

As the death toll from coronavirus continues to rise, some speculate that the rise in temperature from the arrival of spring in the northern hemisphere could delay or even end the spread of the disease. US President Donald Trump made reference to this: "Heat, in general terms, kills this type of virus." You're right?

The idea that spring can stop the spread of the disease comes largely from the comparison with the common cold. In many ways COVID-19 is like a cold: both are transmitted in similar ways (respiratory secretions and contaminated surfaces) and both cause typically mild respiratory illnesses that can develop into life-threatening pneumonia.

But the transmissibility and severity of COVID-19 are much higher than that of a cold. And it is unclear whether COVID-19 transmissions will be affected by seasonal temperature variation.

For flu, the onset of spring causes a significant drop in case numbers that persists until the return of the lower temperatures in the fall. This seasonality of influenza is believed to be caused by the sensitivity of the virus to different climates and by seasonal changes in the human immune system and in our behavioral patterns.

First, the flu virus seems to survive best in cold, dry climates, with a shortage of ultraviolet light.

Second, for many of us, shorter winter days lead to low levels of Vitamin D and melatonin, which can affect the performance of our immune systems.

Third, in winter we spend more time with other people, indoors and closer to each other, increasing opportunities for virus transmission.

Comparison with other coronaviruses

So how might these factors affect coronavirus transmission? It is unclear what effect temperature and humidity have on the coronavirus itself, or its transmission. Other coronaviruses are seasonal, causing common colds in the winter months.

The 2002-2003 SARS epidemic also began in the northern hemisphere winter and ended in July 2003, with a small resurgence in the following winter. SARS cases peaked in the hot month of May and the end of the epidemic in July, which may simply reflect the time required for virus containment rather than an effect of weather on virus transmission. Furthermore, the related coronavirus, Mers, is transmitted mainly in hot countries.

Returning to the comparison with the flu, the 2009-2010 human influenza virus (H1N1) pandemic began in the northern hemisphere spring, increased sharply during that season and summer, and peaked in the following winter. This suggests that in a pandemic, due to the high number of cases in many countries of the world, the continuous transmission of the virus can occur during the summer, overcoming any seasonal variation that would be seen in smaller epidemics.

Therefore, the proximity of warmer climates may reduce viral transmission in the northern hemisphere (while potentially increasing transmission in the coming winter of the southern hemisphere), but it is highly unlikely that the climate itself can end this epidemic in expansion.

Translation by Emilia Guzmán for CIPER Chile.

Jeremy Rossman, Honorary Senior Lecturer in Virology and President of Research-Aid Networks, University of Kent

This article was originally published in The Conversation. Read the original.