No, cold weather does not kill respiratory viruses – in fact, it does the opposite

A local infectious diseases expert and a PLOS research study conclude cold, dry weather makes it easier for respiratory viruses to spread.

WINSTON-SALEM, N.C. — The thermometer is dropping, almost in cadence with the COVID-19 case count, and holiday gatherings look promising.

Nationwide and here at home, data shows big strides fighting COVID-19. But, health experts have cautioned the finish line is not quite within reach.

THE QUESTION

Viewer Carol Harris claimed, "We need a good freeze to kill all these germs."

Is it true a freeze, or even just cold weather, can kill viruses like COVID-19 and the flu?

THE SOURCES

THE ANSWER

This is false.

No, a cold freeze does not kill viruses. In fact, it does the opposite, facilitating spread.

WHAT WE FOUND

Infectious diseases physician Chris Ohl, MD explained, "Respiratory viruses, in particular, they transmit differently, because where do they live? They live inside people, and they thrive inside people, and they transmit from person to person, particularly when we're indoors."

He said respiratory tract infectious go up when it's colder, especially in the wintertime.

"With COVID right now, we're seeing it. The Delta wave has moved up to the northern part of the U.S., and they're having the problem now," Ohl noted.

It's the same reason the flu typically peaks in wintertime. In a 2007 research study published in PLOS Pathogens, scientists used guinea pigs to monitor how they spread respiratory viruses in different temperatures and relative humidity. They found flu spreads much more easily at dry, cold temperatures than warm temperatures with high relative humidity.

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One theory researchers devised is because cool, dry air loosens the nasal mucus and makes it easier for viral particles to get into the respiratory tract.

But, this study left a big question: why, then, do warm and humid climates, like that of Florida, still have flu seasons? The researchers suggested in tropical regions, viruses spread more commonly through contact with surfaces, rather than through the air. Also, people spend more time indoors to escape the heat, and as Dr. Ohl said, it's easier for respiratory viruses to spread in indoor settings.

SOURCE OF MISINFORMATION

How did this claim -- of a cold freeze killing viruses -- originate? Dr. Ohl speculates it's an old wives' tale that dates back centuries.

"I don’t know for sure, but (perhaps it's) from the days when we had a lot of mosquito-borne infections -- malaria, yellow fever -- and these things existed even in NC. So, if you get two hard freezes, it kills all the mosquitoes, and you don’t get any transmission of mosquito-borne viruses anymore. Same thing with tick-borne diseases. Two hard freezes, and ticks go to sleep," he explained.

But, the viruses those pest carry are not respiratory, and they spread through bites instead of aerosol droplets.

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