Cochrane: ‘No evidence for large-scale use of mouth masks’

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Robin Utrecht/ANP

The large-scale wearing of face masks probably has little or no effect on preventing the spread of influenza-like diseases, such as covid-19. Tom Jefferson et al conclude this in an update of a Cochrane review.

Governments around the world have introduced mandatory face masks in recent years, while the scientific evidence for widespread use of face masks has been limited. “Governments have completely failed to do the right thing and demand better evidence,” said epidemiologist Tom Jefferson, lead author of the Cochrane review, in an exclusive interview. The fact that governments nevertheless introduced a mask obligation, according to him, has to do with the fact that they wanted to show that they were ‘doing something’ to combat the pandemic.

There is still no convincing evidence that mouth-nose masks are effective in the entire population, write the authors of the recent Cochrane update. ‘That doesn’t surprise me’, responds Heiman Wertheim, head of the Medical Microbiology department and head of the Center for Infectious Diseases at Radboudumc. ‘Transmission is more complex than we think. In China, for example, where they wear mouth-nose masks en masse, the virus is also just circulating.’

The fact that the evidence for the effect of face masks in the population is limited does not mean that face masks are useless. According to Wertheim, the effectiveness of mouth-nose masks depends on various factors, such as behaviour, how you wear a mouth-nose mask, someone’s symptoms, where you go and when you take off a mask. ‘The large-scale wearing of mouth-nose masks probably slows down the spread, but to a limited extent. Vaccinations are the only way out of such a pandemic. Lockdown measures such as staying at home are of course also effective, but socially very far-reaching and cannot actually last too long without damage in other areas.

Dutch situation

A large-scale study by Jason Abaluck et al. in six hundred villages in Bangladesh suggests that face masks are effective in the population. In this study, published in Science, the researchers stimulated face mask use in part of the villages. The number of SARS-CoV-2 infections decreased when villagers used face masks more often. However, a re-analysis of this study showed that this effect is also probably moderate and possibly even absent.

Wertheim: ‘The fact that they conclude in Bangladesh that face masks are effective does not mean – apart from the reanalysis that calls this into question – that they are also effective in the Netherlands. For example, there were meetings mainly in the mosque, where people probably kept their masks on all the time. You cannot translate that to the Dutch situation, where people have gatherings where the mask usually goes off, such as in a café or restaurant. We also saw transmission among healthcare workers mainly in the coffee room where the masks went off.’

Mouth-nose masks are effective in specific situations in the Netherlands, according to Wertheim. ‘In the hospital I would never advise not to wear a mask, because we see that it works there. The same applies to vulnerable patients.’

The review and the methods used are also criticized. Wertheim: ‘You would prefer to see a few things differently. For example, the authors have lumped studies into mouth masks in society and in the hospital, and there are relatively few covid-19 studies. It’s not the best collection of trials to do a meta-analysis on.’ But according to Wertheim, that does not detract from the conclusion: ‘There is no hard evidence for the effect of mouth-nose masks in the population, however nice that may sound in theory. It is a missed opportunity that during this “pandemic testing ground” that we have now had for three years, we have not invested more in proper studies into the effectiveness of mouth-nose masks.’


The review also states that the authors are ‘highly uncertain’ about the effect of N95/P2 masks compared to surgical masks in the prevention of clinical respiratory diseases. ‘Surgical mouth-nose masks can do more than some people think, and are not just a piece of cloth. There is a filter with three different layers and splash protection. They are also made of the same material as the N95 masks: meltblown polypropylene, which can also filter out the electrical charge of particles,’ says Wertheim.

In Germany, everyone had to wear N95 masks without any clear arguments, which Wertheim thinks is disproportionate. “You mustn’t forget that there is an entire industry behind those masks, which tries to encourage the use of these masks and also regularly delivers poor, unusable quality.” The FMS guideline Personal protection in the (outpatient) clinical setting due to SARS-CoV-2 states that surgical mouth masks type IIR are sufficient in most healthcare situations (except for aerosol-forming actions in both suspected and proven covid-19 patients). ‘And that has been going according to plan for three years now and is proportional,’ says Wertheim.




Exclusive Interview:

Guideline FMS: GUIDELINE PPE SARS-COV-2 V5.pdf (

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