Research confirms that masks are effective in reducing disease transmission, and calls for greater public understanding

A recent study published in the journal Clinical Microbiology Review, The researchers summarised the evidence on the benefits, practicality, drawbacks and impacts of masks and mask-wearing.

The safety, effectiveness, and acceptability of masks and face coverings are among the key and controversial issues of the COVID-19 pandemic. Masks have long been used to reduce transmission of respiratory diseases, both endemic and epidemic. However, a 2023 Cochrane review found that masks are ineffective, which some interpreted as meaning that mandatory mask wearing was ineffective. This widely reported polarization of scientific opinion highlights the need for a new review of masks/masking. Therefore, in this study, we examined the benefits, practicality, and harms of masks/masking.

Masks and respirators for preventing respiratory infections: a review of the state of the scienceImage credit: Ulza / Shutterstock

Methodological challenges

Several methodological challenges hinder the design of high-quality randomized controlled trials (RCTs) comparing masked and control interventions. Common criteria for quality in RCTs of complex interventions are sample size and strategy, setting, piloting and optimization of the intervention, compliance, outcome measurement, side effects, and follow-up, which are difficult to meet in RCTs.

Furthermore, the outcome of mask trials is an infectious disease that can be transmitted from person to person. Trials of communicable infectious diseases, unlike trials of non-communicable diseases, can have an impact on non-targeted individuals by preventing the infection from spreading, meaning that preventing infection in one person can prevent further chains of infection.

Therefore, taking this into account, clinical trials of respiratory protection should be cluster randomized with no contact between clusters. Furthermore, trials of mask wearing conducted when disease prevalence is low may lead to the erroneous conclusion that masks are not effective. Moreover, meta-analyses often incorrectly aggregate different interventions, for example combining trials recommending mask wearing at home because a family member is sick with trials recommending mask wearing outdoors.

New meta-analysis of RCTs

To address these concerns, the researchers used a random-effects model to meta-analyze published RCTs, separating out different interventions, settings, and outcome measures. Q and I-squared statistics were used to assess heterogeneity. Differences between studies were explored using restricted maximum likelihood estimation.

Efficacy The effectiveness of masks was analysed separately in healthcare and community settings. In community trials, mask and mask plus hand hygiene RCTs were analysed separately. In addition, data on continuous mask use and targeted (intermittent) mask use were assessed separately. This reanalysis of RCTs showed that across community RCTs, the incidence of influenza-like illness (ILI) was significantly lower in mask groups than in controls.

A community trial of masks and hand hygiene found that the combined mask and hand hygiene group had a significantly lower incidence of influenza compared with a no-mask control group.An RCT comparing N95 masks with medical masks in a healthcare setting found a significantly lower incidence of ILI in the N95 group.An analysis of the same RCT divided into continuous and intermittent use revealed that continuous N95 use provided a significant protective effect against clinical respiratory disease.

Non- evidence on mask effectiveness

Early in the COVID-19 pandemic, when randomized controlled trials of masks were not available, a systematic review and meta-analysis of observational studies reported that respirators and masks reduced the risk of infection by 85%. Additionally, a school-based cohort study found that teacher mask use reduced the risk of COVID-19 among student household members by 30% to 40%.

Case-control and cohort studies of healthcare workers have provided preliminary evidence of a significant reduction in COVID-19 risk associated with continuous and consistent respirator use. One 2020 study found that hospital staff using N95 respirators in respiratory, intensive care, and infectious diseases departments were over 400 times less likely to acquire occupational COVID-19 compared with staff in other departments (who did not wear masks continuously).

Harm and adverse effects of masks

Side effects from masks do not necessarily mean that mask use is a contraindication, just as side effects from medications are not necessarily a contraindication. However, it is important to understand and address the side effects. Side effects can be categorized as general side effects, side effects in specific risk groups, side effects people experience when others around them are wearing masks, and environmental harm.

Mask wearers may experience skin irritation, mechanical irritation, Acnepressure effects are also expected. Headaches are also expected, increasing with prolonged use. Heat discomfort may occur, especially for healthcare workers wearing personal protective equipment. Speculative claims of harm have been made, but consistent findings across multiple studies reveal no significant, clinically meaningful harm.

Conclusion

Taken together, this study, which considered evidence from a range of study designs and disciplines, is consistent with recent calls to move from a “measurement framework” that draws primarily/solely from RCTs to a “discussion framework” that includes a systematic evidence synthesis approach from multiple study designs.

The claim that masks are ineffective is false. Because masks are effective, albeit imperfectly, improving understanding of mask and respirator effectiveness among clinicians, scientists, policymakers, and the public is an immediate priority. Furthermore, policies regarding masks should (better) reflect actual risks and harms, rather than being influenced by speculative claims.

Research into new materials that may improve comfort and reduce breathing resistance must continue. Plastic medical masks that are uncomfortable, poorly fitting, and made from non-biodegradable materials must be phased out. Finally, the significant threat that anti-mask rhetoric poses to global health and the general public must be recognized and addressed.