Hot and humid, or warmer and drier? How weather affects the COVID-19 spread

INDIANAPOLIS (WISH) — First, the coronavirus lived longer in humid air.

Now, scientists warn it’s transmitted more easily through dry air.

So, which one is it?

News 8 spoke with Dr. Cole Beeler, infectious disease specialist at IU Health. He discussed what we really know so far about how weather affects the spread of COVID-19.

Gillis: We’re talking about how the coronavirus can live in the air…there is a link between the weather and the strength of the virus. First we were concerned about humid air…previously we talked about researchers claiming it was 23 times more potent in humid air. This week a study came out saying we should be concerned about dry air. Which one is it?

Beeler: It’s kind of a law with medical literature. For each study there is an equal, but opposite study in the other direction. I think this more recent study showing that dry air favors transmission for respiratory viruses is more in line with what I think the common knowledge is. The rationale behind that is that in general when you cough and you make respiratory droplets– now matter what the size–they are floating through the air and they are going to accumulate humidity. 

So, the ambient water that’s in the air is going to glom onto these droplets and make them heavier and make them hit the ground faster. 

In dry air, specifically when it gets colder out, there is not as much water in the air so it doesn’t glom on as well. And smaller droplets actually can hang around in the air for longer periods of time. So, there is the potential concern that in drier environments that respiratory viruses may hang around for a little bit longer in the air. 

Gillis: Science starts in a laboratory. But how do we help the public understand how research in a lab doesn’t necessarily translate into real life settings?

Beeler:  Experimental conditions are just those. They are invivo, in a test tube…in an experimental setting where scientists are trying to answer a question and are isolating as many variables as possible. So, you’re kind of looking at a pure picture. 

But life is anything but that. In the real world compared to invivo there are multiple variables that actually contribute to how diseases spread. Just because this study suggests that dry temperatures may allow this virus to be infectious over longer distances or longer periods does not mean that’s what we’re actually seeing invivo or epidemiologically. 

I think what we’re seeing is really the opposite of that, regardless of humidity, that this virus tends to spread in a close radius around someone who’s infected as opposed to longer distances. 

So, while humidity may be concerning from a strict aerosol, physics perspective as to whether or not it affects transmission of the virus and if we see increasing spread of this in our community is yet to be determined. 

Gillis: There have been so many amazing contributions from researchers studying COVID-19 and getting us a clearer picture of what this disease is all about. But In your opinion, do you think these studies are rushed out to the public too quickly and resulting in a sense of mistrust? Because, again, these two studies came out in the same week. 

Beeler:  I think it’s very difficult to know the right answer to that. And this is a great question. I think we’ve been struggling with this in the medical community and it’s really hard to know what to trust. There is this thirst for knowledge just as there is with any community. But at times that bypassess the rigorous methods we’ve set up with peer reviewed journals to make sure what we are publishing are internally valid, that are consistent with the experimental design and that there are no errors that are plugged in there. 

So, there has been this push to get information out there. But I would just advise caution. One study is just one study. There are various qualities of evidence. You need to weigh it against what the current paradigm is as it relates to how diseases spread and how the virus works. We’re learning new things every day. And a lot of the stuff we’re learning now will be reversed a month from now. So, I think all of us have to have a certain degree of humility when it comes to this virus and understand we really don’t know a whole lot about it. We’re learning more, but everything we learn could potentially be changed in the near future. We just need to be cautious with recommendations. 

News 8’s medical reporter, Dr. Mary Elizabeth Gillis, D.Ed., is a classically trained medical physiologist and biobehavioral research scientist. She has been a health, medical and science reporter for over 5 years. Her work has been featured in national media outlets. You can follow her on Instagram @reportergillis and Facebook @DrMaryGillis.