Will heat kill the coronavirus?

We don't know if changing seasons will help stem the outbreak, says Michael Le Page.

WILL the covid-19 outbreakcaused by the new coronavirus fade as winter in the northern hemisphere comes to an end? This has been suggested by some researchers and repeated by some political leaders, including US president Donald Trump.

“We absolutely don't know that,” says Trudie Lang at the University of Oxford. “I keep asking virologist colleagues this and nobody knows. So when you hear people say the weather will warm up and it will just disappear, it's a very unhelpful generalisation.”

This is essentially what Trump said on 10 February. “The heat, generally speaking, kills this kind of virus,” he told a meeting. “A lot of people think that goes away in April as the heat comes in.”

Trump isn't the only politician to make this sort of claim. The UK's health secretary, Matt Hancock, recently told ITV reporter Tom Clarke that the hope was to slow the spread of the virus so any epidemic reaches the UK in spring and summer when coronaviruses, of which the new virus is just a specific example, are less transmissible.

One scenario is that it will burn itself out in summer, another that it will reduce but then return in winter

It is thought the virus – known as 2019-nCoV – can survive for up to four days on surfaces. Some researchers, including Paul Hunter at the University of East Anglia, UK, do think the new coronavirus won't survive for as long in warmer conditions.

“One extreme scenario is that it will burn itself out sometime in the summer,” says Hunter. “The other extreme scenario is that it will reduce in the summer but it will come back again in the winter and become what we call endemic, in that it will spread pretty much everywhere.”

However, if it is more infectious in cooler conditions, there is an increased chance of it spreading faster in the southern hemisphere as conditions there cool in the coming months. David Heymann at the London School of Hygiene and Tropical Medicine, who led the global response to the SARS coronavirus outbreak in 2003, points out that the MERS coronavirus has spread in Saudi Arabia in August, when it is very hot. “These viruses can certainly spread during high temperature seasons,” he says.

It is thought one reason why flu spreads less readily in summer is that people spend less time together in confined spaces. In particular, it could be linked to school closures, says John Edmunds, also at the London School of Hygiene and Tropical Medicine.

However, children tend to spread flu because they have less immunity to it than adults, who have been exposed to many strains. This isn't the case for the new coronavirus: fewer cases have been reported in young people, though this may be just because they are less likely to become seriously ill.

The World Health Organization says we don't know yet how heat and humidity affect the virus. “There is currently no data available on stability of 2019-nCoV on surfaces,” it says in its guidance on preventing infections.

Find out how mathematics is key to understanding the spread of the new coronavirus on page 23