Masking against COVID-19, yes or no?

Some governments are using the mandatory or voluntary use of masks for political gain, for there are many people who do not like them, and the rulers think that lifting the obligation can give them votes. Some people deny that masking does prevent contagion, despite the fact that the use of masks to prevent the transmission of a respiratory disease is common sense. Is there any scientific study that clarifies the situation?

In fact, there are quite a few studies addressing this problem. Let's look at this recent article, published on March 9, 2022, which analyzes the evolution of the pandemic in schools, one of the few environments where it is possible to obtain reliable figures that distinguish between the consequences of the use or rejection of protective masks.

To begin, let's look at a few concepts:

• Primary transmission of the disease: when a case is positive, if the source of transmission is known, it is called a primary transmission.
• Secondary transmission: the number of cases that appear during the incubation period among contacts of primary transmission cases.
• Tertiary transmission: the number of cases that appear during the incubation period among contacts of secondary transmission cases.
• And so on.

Between July 26 and December 13, 2021, the aforementioned study analyzed all identified cases of the (then dominant) delta variant of the COVID-19 coronavirus in schools in 61 school districts in nine US states, which added a total of 1,112,899 students and 157,069 education staff. In 46 districts, the use of masks was mandatory; in 9 districts, its use was only partial; in the remaining 6 districts, its use was voluntary.

The results of the study were as follows:

• A total of 40,601 cases of COVID-19 were detected, identified as primary transmission, because the source from which the patients had been infected was outside the school.
• The number of secondary cases, which were infected in the school itself, was 3,085, less than 10% of the primary cases.

The distribution of secondary cases according to the protection measures in schools was as follows: 

• In schools with voluntary masks, there were 0.264 secondary transmissions per primary transmission.
• In schools with partial protection there were 0.11 secondary transmissions per primary transmission, less than half the preceding case.
• In schools with mandatory masks, there were 0.073 secondary transmissions per primary transmission: 1.5 times less than the second type of schools, and 3.6 times less than schools with voluntary protection.

It can be deduced that, if all schools had made mask use voluntary, the number of cases of secondary transmission would have been at least three times higher than it was: around 10,000 cases instead of the 3,085 that were detected. Therefore, the masks prevented at least 70% of infections.

Of all the procedures that have been used against COVID-19, masks are at least as useful as vaccines. Please, politicians, stop seeking votes from the use of the masks and employ procedures whose effectiveness has been scientifically proven.

The same post in Spanish

Thematic Thread about Medicine and Linguistics: Previous Next

Manuel Alfonseca