From the comments, on coronavirus and humidity

By Tyler Cowen

I am not convinced by the humidity hypothesis, as I don’t see it having much macro explanatory power globally, but I find the questions very important.  On New York City, I tend to blame all those cramped indoor spaces combined with bad ventilation systems, but that too is an unconfirmed hypothesis.  Anyway, here are the words of Daniel Hess:

Dear Tyler and Alex –

As you know the case fatality rate from COVID has been dropping dramatically from COVID. Many have suggested age profile and treatment advances are the cause urge you to consider indoor humidity as the biggest variable. It is *the* governing environmental variable for respiratory health, above all others and it is an accessible way for everyone to improve respiratory health. Urgently, CFR is likely to return in the fall and winter to its previously high levels unless this knowledge can be more widely disseminated.

The idea that the COVID death rate is dropping so rapidly primarily because of age or improvements in medicine does not explain why tropical and humid areas never had high death rates in the first place. Or why the CFR in the southeast was always lower than in the northeast, even before understanding of COVID improved.

Just look at these numbers (see table below) fresh from this morning from worldometers.info :

In Florida deaths/confirmed case is 0.015 but in New York it is 0.073. Is Florida medicine and age profile so much better than New York’s? Florida is a very old state and medicine is not regarded as more advanced in Florida than in New York. Both had to deal with COVID early and Florida’s age profile is particularly skewed old. In fact Florida is typically the retirement destination for aging New Yorkers.

In Mississippi deaths/confirmed case is 0.028 but in Massachusetts it is 0.072. Is Mississippi medicine and age profile so much better than Massachusetts’s? Mississippi is very poor and 40% black, and known to lag socioeconomically. Massachusetts is very wealthy and just 7% black, and known for its advanced medicine and socioeconomic success. If anything, you would expect a much higher CFR in Mississippi than in Massachusetts. But Massachusetts has cold winters, which translates into dry indoor air in the colder months.

In Georgia and Alabama, deaths/confirmed case are 0.019 and 0.017 respectively. In Michigan and Connecticut they are 0.069 and 0.088 respectively. Is Georgia so much younger and medically superior to Michigan? Is impoverished and 30% black Alabama so much younger and more medically advanced than wealthy Connecticut which is just 10% black? Of course not. You would expect Alabama to have a much higher CFR than Connecticut, but instead it is more than 5 times lower. This is an incredibly dramatic difference that is inexplicable until you realize that humidity (including indoor humidity) governs respiratory health to a very large extent.

It seems certain that seasonality plays a role, but more specifically indoor humidity. That is to say, where humidity seems to be most crucial is in reducing severity of symptoms and mortality for those already infected with COVID-19.

That was the finding of a group of 51 scientists in this new paper:

https://www.medrxiv.org/content/10.1101/2020.07.11.20147157v2.full.pdf

“Severity of COVID-19 in Europe decreased significantly between March and May and the seasonality of COVID-19 is the most likely explanation. Mucosal barrier and mucociliary clearance can significantly decrease viral load and disease progression, and their inactivation by low relative humidity of indoor air might significantly contribute to severity of the disease. ”

Innate respiratory immunity is impaired in conditions of low humidity, as has been shown extensively in this large review of the literature by a group led by renowned virologist Professor Akiko Iwasaki of Yale University. In fact, this may be the most comprehensive review of respiratory infection seasonality published anywhere:

https://www.annualreviews.org/doi/pdf/10.1146/annurev-virology-012420-022445

Folks, this is huge because it shows that a simple remedy (indoor humidification in temperate areas in winter months) can cut COVID-19 mortality by almost an order of magnitude.

Humidity as protection against respiratory infections is not new or surprising. Parents have been using humidifiers in nurseries for this reason for generations. Yet somehow, when it comes to COVID-19, all this knowledge is ignored. Madness!

Here is Alex’s source post, and there are a few interesting responses in the ensuing discussion.