Why is the reported number of COVID-19 cases rise across Europe now? Many countries ended their full lockdowns at the beginning of summer, but it wasn’t until the fall that the virus began to spread significantly again in most places. The reopening of schools and universities resulted in an increased mix of people from different households. But could the drop in outside temperatures also play a role?
We know that more people get colds and flu in the winter (The colds can be caused by types of coronavirus) but there are several possible reasons for this. It is often attributed to the fact that people spend more time indoors when it’s colder, cough, sneeze and breathe on each other.
In cold and wet weather, opting for the option of taking a crowded bus or train is more likely than getting to work on foot or by bike. Another theory is that humans produce less vitamin D. when there is less sunlight and so have a weaker immune system.
However, studies have shown that the annual increase in colds and flu is particularly high coincides with when the outside temperature and the relative humidity inside are lower. Influenza viruses survive and are more easily transmitted in cold, dry air. So it’s reasonable to believe that the the same may be true for the COVID-19 coronavirus SARS-CoV-2, which has a similar size and structure.
Laboratory experiments coronaviruses and similar viruses have shown that they do not survive well on surfaces at high temperature and relative humidity, but a comfortable room temperature could be an ideal environment for several days. And they can stop at cooling temperatures (4 ° C) and low relative humidity a month or more.
Coincidentally, there have been repeated reports of COVID outbreaks among workers in Meat packing factorieswho work in such conditions. In factories like this, however, many people work closely together and scream to be heard over the noise of machines the facts suggest may be more likely to spread the virus. They shared living conditions could also promote the transmission.
The lessons from the other coronaviruses that emerged in the 21st century (SARS-CoV and MERS-CoV) also tell a slightly different story. A study Tracking of the weather during the 2003 Sars epidemic in China suggested that the peak of infections occurred in spring-like weather conditions. (There was no way to confirm this through follow-up studies as the virus later became extinct.)
Regular outbreaks of Mers also happen in spring (March to May) in the Middle East. However, this may have less to do with weather and more to do with camel biology. Humans can acquire mers from each other or from camels. Young camels are a major source of infection and new animals are born in March.
We can also see what happened there in the winter in the southern hemisphere. South Africa reported over 700,000 Cases and peaked in July, but New Zealand controlled the infection very well and had fewer than 2,000 cases of COVID-19.
These two countries are very different in many ways, so it doesn’t make sense to compare them directly. But it seems that the colder weather in July and August probably wasn’t the main factor in deciding their infection rates. New Zealand appears to have kept the spread of SARS-CoV-2 in check due to its geographic location, the quality of the health system, and the effectiveness of the public health response. It could have done that in any weather.
Early dates from Australia suggested that low humidity should be a factor to look out for and a better indicator of the risk of a COVID-19 spike than temperature. However, there was a major outbreak in Melbourne in July that coincided with cold weather. This resulted in a strict lockdown, but it was only relaxed completely in October.
Overall, it seems like a good idea to be prepared for more COVID-19 cases in the colder months. However, we have certainly learned from SARS-CoV-2 that new viruses can surprise us.
We also know that close contact with others creates the opportunity for the virus to spread in any weather. So we need to keep a physical distance between people who do not live in the same household and, if possible, continue to wear face coverings indoors.
Unfortunately, we will only learn exactly how weather changes will affect the pandemic if we live through them.