Wearing a mask helps reduce the spread of COVID-19; social media posts misinterpret Annals of Internal Medicine study on N95 respirators

COMPLETE CLAIM: “A randomized controlled trial (RCT), the gold standard for scientific evidence in the medical community, was published Tuesday in the Annals of Internal Medicine. The results of the RCT study deal a blow to proponents of N95 and surgical masks as effective ways to “stop Covid”. » ; a Danish study “showed that there was no statistically significant difference in the risk of Covid between wearing a mask and not wearing a mask”

EXAM

A study in the peer-reviewed journal Annals of Internal Medicine, published in late November 2022, sparked new discussion about the effectiveness of mask-wearing against COVID-19^[1]. According to social media analytics tool Buzzsumo, the study received more than 4,500 user engagements on Facebook, Twitter and Reddit.

The study examined 1,009 healthcare workers from 29 healthcare facilities in Canada, Israel, Pakistan and Egypt between May 2020 and March 2022. Participants were randomized into two groups: medical masks (also called surgical masks ) or N95 respirators, with the aim of determining which mask was more successful in preventing people from catching COVID-19. Between the two, N95 respirators are considered to offer more protection, given that they adapt better to the face compared to medical masks.

Researchers reported that PCR-confirmed COVID-19 cases occurred in approximately 10% of participants in the medical mask group, which was quite similar to cases in the N95 respirator group (approximately 9%). This led the researchers to conclude that medical masks were not inferior to N95 respirators.

However, many social media users interpreted the study to mean that wearing a mask is ineffective in reducing the spread of COVID-19, as this tweet by art dealer Eli Klein who proclaimed “Masks barely work, if at all”. An article published by the site Becker News, which was also shared on social media, ran in a similar vein, saying that “the ‘Gold Standard’ scientific trial deals a massive blow to N95 and surgical masks as a way to ‘stop Covid'”. This article received more than 12,000 interactions on Twitter, thanks to Kyle Becker’s tweet.

However, Marc Loebthe study’s first author and chair of infectious diseases at McMaster University, told Health Feedback that such an interpretation was inaccurate.

Although the study reported that N95 respirators did not significantly outperform medical masks in preventing COVID-19 cases, the study did not include a group that did not wear a mask. As such, “comments on the absolute effect of the N95 mask or respirator in protecting against COVID-19 cannot be made based on our trial,” Loeb cautioned.

He explained the results thus: “There was a 1.19% increased risk of COVID-19 infection among participants who were assigned to medical masks compared to N95 respirators. This is called the point estimate and is the result that comes closest to the true effect. Confidence intervals around this, i.e. what the possible results might be if the test were repeated several times, range from -2.5% to 4.9%. This means that the risk of COVID-19 infection among those using the medical masks could have ranged from a 2.5% risk reduction to a 4.9% increased risk.”

In the study, the authors acknowledged several limitations. For example, study participants might have been infected with SARS-CoV-2 outside of the healthcare setting, when they were not wearing masks. Since an intervention can only work when applied, the number of COVID-19 cases in both groups is not necessarily related to the effectiveness of the type of face masks.

Other experts, who were not involved in the study, also discussed a few other caveats in an article by the Center for Infectious Disease Research and Policy at the University of Minnesota. One of those is that healthcare workers could use N95 respirators if at any time they thought it was necessary, even if they had been randomized to the medical mask group. Such a mix of multiple interventions makes it difficult to attribute the observed effect to a specific intervention.

The Becker News article also quoted “a famous danish studywhich would have found “no statistically significant difference in the risk of Covid between wearing a mask and not wearing a mask”. However, this is not what the study aimed to determine, as a previous health feedback review reported. Instead, the Danish study was designed to determine whether recommend that people wear face masks reduces their risk of COVID-19 infection by 50%^[2]. In effect, an editorial by the Annals of Internal Medicine, which published the study, also clarified this point. Additionally, the authors said their findings were “inconclusive.”

Additionally, the Danish study only assessed the ability of face masks to protect the wearer. Therefore, the study does not address the effectiveness of wearing face masks in reducing the spread of COVID-19 from an infected person to an uninfected person (source control). This is the basis of the recommendation even for healthy people to wear masks, as infected people do not always show symptoms.

The first author of the Danish study, Henning Bundgaard, says Forbes that “Even a small degree of protection is worth using face masks”.

Health Feedback attempted to contact Becker for comment via the email address provided on the Becker News website, but without success.

The discoveries of several peer-reviewed studies support community mask wearing as a useful measure to reduce the spread of COVID-19. Loeb cited a study from Bangladesh, which he considered to provide “one of the best estimates of the absolute effect of surgical masks in the community.”^[3]. The study reported that the group receiving multiple mask-promoting interventions, including the distribution of free masks, had about a 10% reduction in the number of people infected, compared to the control group that received no intervention.

A study in Johnson County, Iowareported that when an uninfected person and an infected person both wore a face mask, the secondary attack rate – the rate at which the infected person passes the infection on to the initially uninfected person – was reduced by half, from from 25.6% to 12.5%^[4]. A similar benefit has also been reported in a study of Beijing householdswhich found 79% effectiveness in reducing transmission between an infected person and family members living in the same household, when both parties wore masks^[5].

In an article for JAMA Networkscientists from the United States Center for Disease Control and Prevention explained that the benefits of mask-wearing for individuals increase with the number of people who choose to wear masks:

“The overall benefit to the community of wearing masks stems from their combined ability to limit both exhalation and inhalation of infectious virus. Similar to the principle of herd immunity for vaccination, the greater the extent to which the intervention – wearing a mask in this case – is adopted by the community, the greater the benefit for each individual member.”

In summary, Loeb’s study et al. was designed to compare the effectiveness of medical masks with that of N95 respirators to determine which was more effective in protecting people from SARS-CoV-2 infection. It did not compare groups wearing a mask to a group not wearing a mask, therefore the study does not provide evidence that wearing a mask does not work to reduce the spread of COVID-19, unlike the popular interpretations offered by social media. media users. Although wearing a mask cannot prevent COVID-19 with 100% effectiveness, studies show that it can and does significantly reduce the risk of transmission of the virus.

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