As Covid-19 spread through Europe last spring, there were hopes that warm summertime temperature levels would see off the virus – and fears about what winter season may bring.
But in reality, the relationship in between the weather and infection rates appears to be more complicated: chilly Norway and Finland prospered in February, and Spain’s second wave took hold in August.
So what should we anticipate as the weather condition turns?
A cold-loving infection
The problem is that the Sars-CoV-2 infection that causes Covid appears to be much better adapted to wintry conditions than we are.
” All infections endure outside the body much better when it is cold,” states the BBC “The UK’s Scientific Advisory Group for Emergencies (Sage) says a temperature level of 4C is a particular sweet spot for coronavirus.”
According to the Centre of Evidence-Based Medicine(CEBM) at Oxford University, a 1C drop in temperature raises the R number – a procedure of the spread of the epidemic – by about 0.04
So if a break out was steady at 27 C, with 10 transmittable individuals infecting 10 others, reducing the temperature level to 5C would indicate those ten individuals would infect about 20 more, and the epidemic would grow significantly.
The infection is likewise hindered by humidity and UV light – both in short supply on winter days.
” When the weather condition turns cold, air gets drier,” says the medical news site STAT “Turning on the heat dries both the air and the tissues lining the airways, hindering how well mucous eliminates debris and invaders like Sars-CoV-2.”
The human factor
Our own responses to winter also makes life easier for the virus. “We gather indoors as soon as the weather condition turns and beer gardens and Barbeques are less enticing,” says the BBC. “We also slam the windows shut so there is little ventilation.”
The human body immune system performs less well throughout the winter too, which might imply individuals who catch Covid-19 get more seriously ill.
During the spring, scientists tape-recorded “a roughly 15%drop in death for each one degree Celsius rise in temperature”, the Covid Symptom Study reports. As temperatures drop this fall, the pattern may be reversed.
However, says the CEBM, “weather alone can not explain the irregularity” in the spread or severity of the virus. “Confounding” elements such as social distancing and other public health steps might be even more significant.