Does Cold Weather Make COVID-19 Spread More Easily?

Experts warn cold weather can spread the virus faster, but it’s complicated.

Every day it seems we learn something new about the spread of COVID-19. From the effectiveness of mask-wearing to aerosol transmission, the past year has been filled with research and learning about the deadly virus.

As the one of the most frigid times of the year is upon us, many Canadians have a new pressing concern about COVID-19 — the cold, and how the chilling temperatures could make the virus worse.

One thing we do know for sure — cold weather and snow don’t prevent COVID-19, according to the World Health Organization.

“There is no reason to believe that cold weather can kill the new coronavirus or other diseases. The normal human body temperature remains around 36.5°C to 37°C, regardless of the external temperature or weather,” the organization states.

In fact, some research shows cold weather could make the virus even more transmittable.

Here’s what you need to know.

How could cold weather actually make COVID-19 spread?

Because COVID-19 is still so new, research is still being done into how various factors influence its spread. And results are mixed as to how important cold weather can be.

A pre-print study published by a group of researchers in November found that the stability of the novel coronavirus might change with temperature and moisture level. According to their findings, lower temperatures and extreme humidity—both high and low—keep the virus stable and infectious for longer. And this isn’t new. Research has shown other viruses, like influenza, norovirus and other coronaviruses, respond to the cold in the same way — that’s why respiratory virus season is a thing in the winter.

Viruses can spread more easily during cold, dry weather. 
Viruses can spread more easily during cold, dry weather. 

The aerosols expelled by infectious people — and the virus that clings to them — tend to last longer in cool, dry air.

But the study’s authors noted that while temperature can have an impact on the virus’s spread, ventilation and personal protective equipment like masks are still the best way to slow transmission.

“Our results highlight the importance of proper personal protective equipment and improved ventilation for protecting workers, particularly in cold indoor settings, and the general transmission risks associated with indoor gatherings,” the authors wrote.

These cold and dry settings include places that have demonstrated superspreader events, such as meat-packing facilities, ice rinks and long-distance flights.

Other research has affirmed that while cold may be a factor in how the virus spreads, it’s not nearly as important as human behaviour like mask wearing. According to a University of Texas at Austin study published in October, hot or cold weather alone does not have a significant impact on spread.

“The effect of weather is low and other features such as mobility have more impact than weather,” said Dev Niyogi, the professor who led the research. “In terms of relative importance, weather is one of the last parameters.”

Does this mean I should wear a mask outside in the cold?

So should you mask up whenever the temperature drops?

According to Ottawa’s top doctor — yes. Despite previous advice only requiring masks indoors, during an appearance on CBC Radio this week, Dr. Vera Etches said with COVID-19 case rates continuing to skyrocket, people should wear masks outside of the home whenever they can.

Health officials recommend wearing a mask even outside if you're going to be around other people.
Health officials recommend wearing a mask even outside if you're going to be around other people.

“People should wear masks when they’re outside of their house as much as possible. It’s an added barrier. You don’t know if you’re going to come into close contact with someone or not,” Etches said.

Etches added that it’s easy to transmit respiratory droplets outdoors when you’re around other people. So consider masking up if you’re heading to the skating rink or an outdoor market.

Besides, you have the added bonus of keeping your face nice and warm.

How does cold weather impact your body’s ability to fight the virus?

Breathing cold, dry air can impact how our immune systems function. According to a 2015 study, the cells lining the airways of mice produced fewer interferon molecules when they were colder. These molecules sound the alarm about viruses and trigger the immune response.

The same team from Yale University also found that low humidity dries out mucus in our mouths, noses and throats, making it harder to dispel viral invaders.