A large literature study questions the usefulness of face masks against respiratory viruses. Did we wear a mask for nothing for months during the corona crisis, or is it mainly due to the lack of useful research?
How useful are mouth masks? It was one of the most frequently asked questions during the entire corona crisis, and to this day the discussion is occasionally revived. Now it is a new analysis of the famous Cochrane Review that ensures that. Cochrane is internationally known as a thorough research institute that summarizes all available research on medical topics in large overview studies. For their analysis of the usefulness of mouth masks and other measures, the researchers consulted 78 studies with a total of 610,872 participants.
The conclusion? Wearing a face mask of any type appears to make “little to no” difference in stopping the spread of infectious disease. A striking finding, which goes against a lot of previous research on the usefulness of the mouth mask.
“The problem is that a lot of research on face masks is observational,” says Patrick Vankrunkelsven, director of Cebam, the Center for Evidence-Based Medicine that also represents the Belgian division of Cochrane. “Observational research looks at the effect of mouth masks by comparing a group that wore one compared to a group that did not wear a mouth mask. The problem with this is that any differences can also be explained by many other factors. For example, people who wear mouth masks may also be more careful in general and avoid risk areas more often, which gives distorted results.”
Robust research method
For that reason, Cochrane only uses so-called randomized controlled trials (RCTs), which is known as the most robust research method. In this type of research, a group of people is divided into two groups, and attempts are made to filter out as many biases as possible. “You are actually trying to compare two groups that differ as little as possible in terms of risk factors and circumstances, so that you get the best possible picture of the impact of a particular drug or measure,” says Vankrunkelsven.
Cochrane may be rigorous, but there is also a lot of criticism of this research. Because research through randomized controlled trials is very complex and expensive, few of good quality have been carried out since the arrival of the corona virus. Of the 78 studies that Cochrane bundled, only 6 date from the corona period. The other 72 come from the pre-corona period and are about respiratory viruses that resemble corona, but do not behave in exactly the same way. The environments in which the studies took place also vary considerably, ranging from schools to hospitals or migrant neighbourhoods.
A second problem is that most of the studies selected by Cochrane only address the question of the extent to which a mask protects the wearer from becoming infected. “But we know that a mask also protects other people, by stopping the larger droplets from people wearing a mask,” says virologist Marc Van Ranst (KU Leuven). For example, previous research during a flu epidemic showed that if infected people wear a mask, their family or loved ones are less likely to be infected.
The main problem with the research that Cochrane bundles is that it says little about how closely people followed a mouth mask obligation or recommendation. In most studies, the researchers asked people how often they wear a face mask, but it is known that this kind of self-report is usually an overestimate. Cochrane itself indicates that “the relatively low number of people who followed the recommendations may have influenced the research results”.
The under-the-nose mask
In other words: the results often show at most that there is no clear effect of a mouth mask obligation or recommendation, but not that the masks themselves cannot be of any use. “There is a reason why researchers who work in laboratories with dangerous diseases such as rabies, bird flu or corona wear a mask,” says virologist Steven Van Gucht. “A lot of laboratory research has shown that masks can undeniably stop harmful particles, and that is also the case with corona.”
While that is unquestionable on an individual level, it becomes a different story when we look at the effect of face masks on the population level in the real world. “We all know that there are a lot of people who wear the mask under their nose or take it off when they speak. For example, the effect of mouth masks can be diluted,” says Van Gucht.
The authors themselves also indicate that their confidence in the assessment of the effect of mouth masks is rather limited. So if the study shows anything, it is mainly that there is a need for more high-quality studies to estimate the effect of mouth masks against the corona virus.
“It certainly cannot be ruled out that a well-conducted study will give a different result,” says Vankrunkelsven. “In any case, wearing a face mask remains one of the measures that can be useful in an epidemic, but always in combination with other measures.”