Virus spreads fastest at 4C, say scientists

Britain’s climate in January and February found to be perfect for the virus to survive and spread

Government scientists have concluded that coronavirus spreads fastest at 4C, as concern mounts over the threat of a winter resurgence. The Scientific Advisory Group for Emergencies is understood to be focusing on the precise temperature as Melbourne, which is currently in its coldest month, re-entered a six-week lockdown due to a steep increase in cases. Yesterday, a senior Sage member said that Covid-19 “likes” four degrees best – “it survives well at 4C”.

CORONAVIRUS spreads fastest at 4C, government scientists have concluded, amid mounting concern over the threat of a winter resurgence.

The Scientific Advisory Group for Emergencies (Sage) is understood to be focusing on the precise temperature as Melbourne, which is currently in its coldest month, re-entered a six-week lockdown due to a steep spike in cases

On Friday, a senior member said Covid-19 “survives well at four degrees centigrade [Celsius]”.

The view, which helps explain how the virus exploded around the UK in February and March, was later by independent scientists.

However, once below 4C, viral particles begin an intermittent freeze-thaw process which also hastens their decline.

Average temperatures in Britain in January and February have fluctuated between 3C and 5C in three of the past six winters.

Sage is understood to be increasingly confident that countries with temperate climates and with relatively severe flu seasons, such as Britain, will also be affected worse by Covid-19 in winter. Members believe that lapses in social distancing are less harmful in the summer but will cause more significant damage to infection control as Christmas approaches.

There have been a number of outbreaks at meat processing plants, where temperatures are typically kept very cool, although some experts believe there may be other factors.

Yesterday, an evidence summary prepared for Sage on June 12 was released which found that the virus survives on outdoor surfaces 10 times longer in mid-winter than in mid-summer.

Modelling showed that direct midday sunlight in London during the summer reduced infectivity of the virus by 90 per cent after 30 minutes, compared to 300 minutes in winter.

Prof Paul Hunter, a University of East Anglia virus expert who led a review into the impact of temperature in 2017, said: “Viral inactivation is very temperature dependent.”

The latest Covid-19 growth rates show that transmission in the UK dropped slightly in the last week.

Prof James Naismith, director of the Rosalind Franklin Institute, said: “That the number of cases is falling slightly . . . suggests, that so far, relaxation of the lockdown has not precipitated a second wave.

“It has to be emphasised that no one knows what the safe level of relaxation is for the UK and there is a delay between action and consequence.”