Health

The weather can affect the spread of coronavirus. Here’s how

By Geoff Norcross (OPB)
Portland, Ore. Aug. 4, 2020 7:12 p.m.

We’re learning new things every day about the coronavirus and the disease it causes, COVID-19, as they proliferate around the world. But there are gaps in our knowledge and it can be hard to keep up with the science.

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OPB recently checked in with the scientific community about how weather conditions can affect the virus.

Dr. Dawn Nolt is a professor of pediatrics at Oregon Health & Science University and the medical director for infection prevention and control at Doernbecher Children’s Hospital. She spoke with OPB’s Geoff Norcross.

Dr. Dawn Nolt is the medical director for infection prevention at OHSU Doernbecher Children's Hospital.

Dr. Dawn Nolt is the medical director for infection prevention at OHSU Doernbecher Children's Hospital.

OHSU

Geoff Norcross: “So when we first started hearing about this virus, that was in the winter. It was cold, and some were saying it’s not going to be as transmissible when it gets hot and when it gets humid. We’re there now, we’re in summer — so what is the current thinking about how the coronarvirus moves in the heat?”

Dr. Dawn Nolt: “Well, as you said, there’s a lot of interest in how the weather can influence the spread of infection, and COVID-19 certainly has raised that interest. What seems to be bubbling up in the early data is that there may be an inverse correlation — that as the weather goes up and humidity goes up, the number of cases of COVID-19 infection may go down. But the data is still somewhat soft and it’s only a few months old.”

Norcross: “Why might that be? I mean, what is it about the heat that might make the transmissions go down?”

Nolt: “It’s poorly understood what happens once a virus is extruded out off a person after coughing or sneezing. What we’re thinking, though, is the virus has somewhat adapted — that as it gets out into a harsher environment such as a cold or dry environment, it needs to figure out how it can get to the next person. So in a cold and dry environment, the surroundings of the virus get a little lighter. It’s able to travel further, and so we feel that the virus has adapted to a cold, dry environment and therefore can travel further. The inverse being: if it’s hot and humid, the virus could just as easily drop immediately to the ground after it comes out of a person.”

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Norcross: “I understand. So there is a cold and flu season and that’s usually during the cold months. Could we someday see a COVID season?”

Nolt: “It certainly is possible. We know that COVID-19 is a coronavirus and there are other human coronaviruses that circulate. They have a peak activity, as you said, during the winter and even spring months. But right now, there is so much background. There’s so much activity of the virus. But I think it’s obscuring any sort of possible peak or possible season. So we need a little more time until we really figure out if there is a specific season to COVID-19.”

Norcross: “You’ve said that there may be something to the science that suggests that the virus doesn’t move as well in hot weather. But is it really just more us being in the environment? Are people at less risk of contracting the virus because it’s hot outside or because they are outside?”

Nolt: “Right? You raise, Geoff, a really complicated question. We’re not going to say that hot weather is going to make people safer because it makes the virus less infectious. But as you already pointed out, the weather influences human activity. And in some ways, the change in human activity with hot weather could make you at less risk. You get out there in the world, you have more space, and you may be less likely to catch other people’s respiratory secretions.

“But on the other hand, hot weather may get you more out there, make you more mobile and you would actually interact with more people. So it’s difficult to know. I would say that regardless of where you are, whether it’s inside or outside, or if the weather is hot or cold, you have to be careful and do the usual infection control practices that we are always advocating for.”

Norcross: “Are there any places on Earth where the coronavirus that causes COVID-19 just can’t exist? Are there other atmospheric conditions anywhere on this planet where there just is no coronavirus, or can’t be?”

Nolt: “And if I provide an answer, we’ll all move there (laughs). It certainly seems that at extreme conditions the virus will just fall apart. We call this process being denatured. We know that very high temperatures close to boiling will denature the virus. Certain low pHs — being very acidic — will denature the virus, and having a lot of detergent can certainly break down the virus. So I’m not a geologist, Geoff — I’m not sure where those places would be: a very hot place that’s acidic and has a lot of detergent. It doesn’t sound very appealing for me to move there.”

Norcross: Well, that’s part of the problem, is that wherever the coronavirus can’t live, we can’t live either. So the virus is kind of like a little person that likes what we like.”

Nolt: “That’s right. And that’s how it survives in that and is able to infect us.”

To listen to the entire conversation, use the audio player at the top of this story.



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