COVID Transmissions for 9-10-2021

Studying masks in a randomized trial

Greetings from an undisclosed location in my apartment. Welcome to COVID Transmissions.

It has been 660 days since the first documented human case of COVID-19. In 660, Emperor Constans, paranoid about his younger brother Theodosius, has him killed. This makes Constans deeply unpopular, and he flees Constantinople to continue his rule from Syracuse in Sicily.

Today we’ll discuss a rigorous study of the effectiveness of wearing masks against COVID-19. It should be no surprise that they work, but there’s still some solid, interesting data to look at in this new study.

As a reminder, the Jewish holidays are interfering with my schedule somewhat. Next week I expect to write to you on both Monday and Wednesday, but I can’t be sure if I will be able to send out something on Friday, due to Yom Kippur being the immediate day prior.

Bolded terms are linked to the running newsletter glossary.

Keep COVID Transmissions growing by sharing it! Share the newsletter, not the virus. I love talking about science and explaining important concepts in human health, but I rely on all of you to grow the audience for this, which you can do by using this button here:

Now, let’s talk COVID.

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A randomized, controlled study of masking

A recent working paper reports the results of a randomized, controlled study of wearing masks to prevent COVID-19:

This is easily the most rigorous and largest study of masking to date. Hundreds of thousands of people in Bangladesh were included, and there were clearly defined intervention and control groups. The headline is that masks are an effective preventative intervention for COVID-19.

Specifically, the use of a masking-related intervention more than tripled mask wearing from 13.3% to 42.3%. Accompanying this, the authors saw a 9% reduction in COVID-19 prevalence in the mask-intervention population.

The mask intervention was as follows:

All intervention arms received free masks, information on the importance of masking, role modeling by community leaders, and in-person reminders for 8 weeks.

This study was not blinded and the control did not receive any intervention at all.

A 29-point increase in mask wearing led to a 9-point reduction in COVID-19. Imagine, then, what an 80-point increase in mask-wearing might have done. Keep in mind that infectious diseases are just that--so their spread is not linear, with each new case potentially producing additional cases. It is likely that more masking would have more than just a linear impact on COVID-19 rates, because each prevented case also prevents more downstream cases.

I do want to note that this study also compared cloth mask interventions with surgical mask interventions. Some outlets are reporting that it shows that cloth masks are insufficient, but I think this is ill-supported from the data. There is an evident reduction in the rate of reported COVID-19 symptoms in villages where cloth masks were provided compared to controls. A similar reduction is seen in the surgical mask villages. A difference between cloth mask villages and controls was not seen with regard to COVID-19 seroprevalence, but there are a number of reasons this could be the case. For one, the study did not control well for prior outbreaks before the intervention, which could have affected observations on this measure. The authors point this out, in fact. Another point is that it’s possible you need a higher percentage of masked people in the population for cloth masks to have an effect on seroprevalence. Since these types of masks are largely what’s called “source control,” this perhaps makes some sense. It’s possible that with cloth masks, people still get exposed to SARS-CoV-2 enough to seroconvert, but maybe not enough for illness to become established, due to an overall reduction in the amount of circulating virus. Perhaps with more mask compliance--remember this study only got mask wearing to 42.3%--we might have seen effects from cloth masks on both measures. That’s speculation, though.

The thing is, what’s really important here isn’t whether surgical masks are better than cloth masks. It’s that masking is better than not masking. Yes, a surgical mask is probably better source control than a cloth mask, but that’s not really the point of this study. The point is that masks have an impact, by a variety of measures, and that impact stands up to serious, rigorous scientific inquiry.

The study can be found here: https://www.poverty-action.org/publication/impact-community-masking-covid-19-cluster-randomized-trial-bangladesh

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What am I doing to cope with the pandemic? This:

Outdoor Rosh Hashana Services

Last year, after spending months advising the planning of Rosh Hashana services for my synagogue so we could meet in a COVID-safe(r) fashion, I got sick and was unable to attend. I wasn’t severely ill, but I was ill according to the cancellation policies I had set, and I’d have been pretty hypocritical not to observe rules I set myself. The sad thing is, it meant I didn’t get to enjoy the holiday at all.

This year, I actually got to go! It was great! It’s interesting how communal activity, like prayer, can transform a space like a city street into something totally different from what it normally feels like.

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I still owe a number of you email replies to personal messages. Rest assured I am not ignoring you, I am just extremely busy until after Rosh Hashana.

You might have some questions or comments! Send them in. As several folks have figured out, you can also email me if you have a comment that you don’t want to share with the whole group.

Join the conversation, and what you say will impact what I talk about in the next issue.

Also, let me know any other thoughts you might have about the newsletter. I’d like to make sure you’re getting what you want out of this.

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Part of science is identifying and correcting errors. If you find a mistake, please tell me about it.

Though I can’t correct the emailed version after it has been sent, I do update the online post of the newsletter every time a mistake is brought to my attention.

No corrections since last issue.

See you all next time. And don’t forget to share the newsletter if you liked it.

Always,

JS