Does the coronavirus spread easier in cold temperatures? This is...

Why is the reported number of COVID-19 cases increasing 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 during winter (colds can be caused by types of coronaviruses), but there are several possible reasons for this. It is often attributed to people spending more time indoors when it is colder, coughing, sneezing and breathing 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 when there is less sunlight, people produce less vitamin D and therefore have a weaker immune system.

However, studies have shown that the annual rise in colds and flu coincides especially when the outside temperature and relative humidity inside are lower. Influenza viruses survive and are more easily transmitted in cold, dry air. One can therefore assume that this also applies to the COVID-19 coronavirus SARS-CoV-2, which has a similar size and structure.

Laboratory experiments with coronaviruses and similar viruses have shown that they do not survive well on surfaces at high temperatures and relative humidity. However, a comfortable room temperature could be an ideal environment for several days. At cooling temperatures (4 ° C) and low relative humidity, they can take a month or more.

Coincidentally, there have been repeated reports of COVID outbreaks among workers in meat packing factories working in such conditions. In factories like this, however, many people work closely together and scream to be heard over the noise of machines. This suggests that the virus may be more likely to spread. Their common living conditions can also promote 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 that tracked 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 occur in the 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.

Southern Hemisphere

We can also see what happened there in the winter in the southern hemisphere. South Africa has reported over 700,000 cases and saw a major peak 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 data from Australia suggested that low humidity is a major factor in the risk of COVID-19 spikes than temperature. However, in Melbourne there was a major outbreak in July that coincided with cold weather. This resulted in a strict lockdown, but it wasn’t fully relaxed until 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.

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