The New England Journal of Medicine published a paper this week looking at the rates of COVID-19 among students and staff of public schools, some of which had universal masking and others that had lifted their masking mandates. Their analysis shows that schools with mask mandates had lower rates of COVID infections than those that lifted their mask mandates: overall, lifting mask mandates ended up causing an additional 44.9 cases of COVID per 1000 people, or 11,901 extra cases in total, over 15 weeks. The rates among staff alone were even higher, with 81.7 extra cases of COVID per 1000 staff members.
But when I started to look at the data, things didn’t seem so clear.
They used whats called “difference in differences” analysis, which is basically when you try to take a real life situation and make it into a “controlled” experiment. In this situation, 72 public school districts in the Boston area had universal mask mandates, then some lifted them but others didn’t. Two districts kept those mask mandates throughout the whole school year (the “controls”) and the other 70 lifted their mask mandates at various times. The researchers assumed that all these districts were similar in every other respect, and that when (or if) they lifted the mask mandate was the only difference. My first thought was: neighboring schools can INDEED be very, very different, I’ve seen that first hand (hello Plantation High school versus Dillard). The authors themselves indicated that the two districts that kept universal masking were the most highly diverse, had the lowest income students, the least-maintained facilities, the lowest pediatric vaccination rates, etc etc. So, no. Not exactly the same across all schools….our “controlled” experiment may already be not-so-controlled.
Here is their most critical finding:
The greyish line is the school districts that dropped mask mandates the first week after Massachusettes lifted the state mandate, the light blue line is the districts that dropped mandates the next week, and the dark blue line is the districts that dropped mandates the third week. The black line represents the two districts that stayed masked throughout the whole year. As you can see, the fully masked schools had lower student and staff COVID infections than those districts who lifted their mask mandates. But here’s something that struck me.
If the three sets of school districts dropped their mask mandates at different times, then why do their infection rates basically all rise together? If school masking was the only influencer on infection, then you would expect to see the infection rate in the grey line districts go up first, followed by the light blue districts a week later, then the dark blue districts a week after that (week 1, then 2, then 3). But you don’t…. they all track together. In fact, the grey line (those that dropped the mask mandates first) have far fewer COVID infections than the light blue line (the districts that dropped the mandates the following week). Something else is going on here.
A figure in the supplementary material of this paper shows something that does track though….. the rates of COVID infections in the school exactly tracks with the overall rates of COVID in the city/town, regardless of when (first, second or third week of March), or if (panel on bottom right) the school lifted its mask mandate.
This indicates to me that school infection rates are more powerfully influenced by what’s going on in the community than the mask mandates in the school themselves.
Another important point is that this paper only studies MASK MANDATES. Not actual mask wearing itself. Surely, there were many students and staff who continued to mask even after the mandate was lifted, and possibly that percentage of maskers differed from one district to the next (for example, urban versus suburban schools).
And herein lies the problem with observational studies, its easy to assume that there aren’t confounding variables when, in fact, there may be many. Human behavior is, itself, confounding. Unfortunately, many of the published studies on mask wearing are observational and fall into this same trap.
I myself have changed my own view on mask wearing somewhat throughout the whole pandemic. In the beginning (March 22, 2020), I wrote a blog post discouraging people from wearing facemasks. At that point, it was unknown how contagious COVID was, and I was using the theory that most people wont wear masks correctly so they wont be very useful (and may even INCREASE your risk of respiratory disease because many people touch their face more when they are masked, or will handle the mask incorrectly). At that point, the only people I thought should be masked were those that were actually infected (to prevent spreading it to others), those that were at an increased risk for serious disease, or those that were caring for infected persons.
By the following month, I had changed my tune (somewhat). As new data rolled in about the contagiousness of COVID and the number of asymptomatic-yet-contagious persons, I felt that mask wearing was important….not to protect yourself, but to prevent spread in the population. I explained that mask wearing may not protect you from infection (poor fit of mask, incorrect usage, incomplete filtration, the virus can enter the eyes, etc), but that if you were asymptomatically infected, it would prevent you from spreading the virus to others. This relates back to the old theory that masks….
“Protect the world from the wearer, but do not protect the wearer from the world”.
This was also way back in spring of 2020, when there were no vaccines available and community immunity was low. Masking and social distancing were literally the only things that we could do, and it felt good to do SOMETHING. The situation is very different now as most people are either vaccinated, have caught COVID and have natural immunity, or both. A new estimate is that 2/3 of the world has COVID antibodies. While this does not mean that you are impervious to COVID infection (as many of us know!) it does mean that you have at least some immunological protection.
So, my position on masking has changed again. Masking does not seem to be as critical a practice to me considering community immunity is high and the data on masking efficacy is shaky at best.
In the next post, I’ll analyze a few more masking studies… some showing modest benefits, some showing no benefit at all. The data… is in disarray.
Lifting universal masking in schools - COVID-19 incidence among students and staff
Stay happy, healthy and informed,
Jessica at TCA