Face masks during the COVID-19 pandemic
During the COVID-19 pandemic, face masks or coverings, including N95, FFP2, surgical, and cloth masks, have been employed as public and personal health control measures against the spread of SARS-CoV-2, the virus that causes COVID-19.
In community and healthcare settings, the use of face masks is intended as source control to limit transmission of the virus and for personal protection to prevent infection.[1] Properly worn masks both limit the respiratory droplets and aerosols spread by infected individuals and help protect healthy individuals from infection.[2][3]
Reviews of various kinds of scientific studies have concluded that masking is effective in protecting the individual against COVID-19.[2][4][5] Various case-control and population-based studies have also shown that increased levels of masking in a community reduces the spread of SARS-CoV-2,[4][5] though there is a paucity of evidence from randomized controlled trials (RCTs).[6][7] Masks vary in how well they work, with N95 and surgical masks outperforming cloth masks,[8] but even cloth masks, with their variability in fabric type and mask fit, provide wearers with substantial protection from particles carrying COVID-19.[9]
Among readily available fabrics, double-layered cotton, hybrid masks, and cotton flannel perform best,[9] and filtration effectiveness generally improves with thread count.[8] Healthcare workers, given their exposure, are recommended against using cloth masks.[9]
During the public health emergency, governments widely recommended and mandated mask-wearing, and prominent national and intergovernmental health agencies and their leaders recommended the use of masks to reduce transmission, including the WHO, American, European, and Chinese Centers for Disease Control and Prevention.
Efficacy[edit]
Overall[edit]
There are two types of evidence for the efficacy of masks: observational studies, and randomised controlled trials (RCTs). While RCTs are more robust, they are too impractical for many public health interventions, yielding insufficient statistical power and validity.[155] Most of the evidence for the efficacy of masks against COVID comes from observational studies.[156] Due to the paucity of evidence from RCTs, some systematic reviews have included the observational studies along with the RCTs.[7][4] As of August 2023, RCTs played a relatively small role in the evaluation of non-pharmaceutical interventions during the pandemic.[156]
A 2023 systematic review from the Cochrane Collaboration said the evidence from randomized controlled trials was still inconclusive over whether masking prevented the spread of influenza/COVID‐like illness through a population, noting that the answer could be different for different viruses.[6] This Cochrane review was criticized for combining studies about influenza and about COVID, which could "yield invalid conclusions".[155] Another 2023 systematic review, by the Royal Society, found the evidence from RCTs was that masks reduced risk by 12% to 18%.[7]
A 2022 systematic review and meta-analysis of randomized controlled trials on face mask use in PLOS One showed that with 95% confidence, masks reduced respiratory infection incidence by between 3% and 19% in a community setting.[157] A 2023 article in JAMA Network Open found that "robust data" support the use of face masks to reduce community transmission of COVID.[155] A 2023 review in Archives of Disease in Childhood on mask wearing by children found no good clinical evidence that mask wearing was of benefit for them in preventing COVID-19 transmission or infection.[158]
A systematic review and meta-analysis of the effectiveness of masks published in The BMJ in November 2021 showed that with 95% confidence, masks reduced COVID incidence by between 25% and 71%. This result is based on six primary studies. These studies were of several different types: case-control studies in Thailand and three Western countries (where cases identified whether they were wearing a mask when they had contact with a known positive patient), a randomized control study in Denmark which assessed the impact on mask-wearing on the wearer, a natural experiment that compared US states that implemented mask mandates on the level of COVID, a cross-sectional comparative study in China which surveyed whether a mask protected the wearer, and a retrospective cohort study in China which assessed the impact of masks worn by infected and uninfected family members. Another five studies were not included because they were not directly comparable. They assessed the impact of mask mandates across countries on mortality (finding a 45.7% reduction), of mask mandates in the US on R (finding a 29% reduction), a comparative incidence of COVID associated with mask-wearing comparing HK and South Korea (finding a significant reduction), a natural experiment across US states finding a significant effect on case rates, and a cross-sectional study assessing a 10% increase in mask wearing led to a 71% reduction in the risk to others. A lot of other papers had to be rejected because of the risk of confounding influences.[4] Other reviews in 2020 and 2021 found that there is consistent evidence that mask-wearing is effective in reducing the spread of the SARS-CoV-2 virus[5][159] and that population-wide masking proved significant in reducing the transmission of COVID-19.[8][160]
Masks are not of equal efficacy. While N95 masks outperform surgical masks in filtration, healthcare worker population studies have not shown a significant difference between the two, as of June 2021.[8] N95 and surgical masks, both designed for single use, can be decontaminated at a loss to mask integrity and filtration efficacy.[8] Both N95 and surgical outperform cloth masks, which the general public has used based on their greater availability during mask supply shortages.[8] Cloth and fabric masks have protected wearers from COVID-19, with some variability,[9] such as fabric type, layer count, and mask fit.[161] Cloth masks are insufficient for healthcare workers and not recommended, according to two randomized controlled trials.[9] Several observational studies, including four reviewed in a 2020 Lancet meta-analysis, have found that masks offer statistically significant protection from infection, although the level of protection varies according to the mask type and setting.[63]
Clinical evidence of mask efficacy in COVID-19 transmission was limited and had become a subject of scientific debate by May 2021.[162] Clinical studies had not evaluated the efficacy of cloth masks in COVID-19 transmission by the end of 2021.[9] Evaluation of cloth mask efficacy is further complicated by the wide variation in fabric and fit, among other factors.[8] Concerning the precedent of mask efficacy in limiting transmission of respiratory viral illnesses other than COVID, a clinical trial meta-analysis in May 2021 showed no significant evidence of efficacy, though the authors noted the evidence to be poor quality and subject to confounding factors like consistent mask usage adherence.[162]
Cloth masks[edit]
Community studies have shown some cloth masks to be effective at filtering respiratory droplets, which can carry SARS-CoV-2.[8] Cloth masks of a cotton quilt (120 thread per inch), bonded copy paper, flannel, and a chiffon or silk hybrid with cotton are over 90% effective at blocking particles the size droplets that carry SARS-CoV-2, according to an October 2021 review of 42 studies. Multilayered fabrics provided improved breathability and filtration efficacy. Among readily available fabrics, two-layered 100% cotton, two-layered cotton quilt, hybrid masks, and cotton flannel performed best.[9] Filtration effectiveness generally improves with thread count.[8]
The use of a face mask can result in significant risk reduction of infection with epidemic-causative beta coronaviruses. N95 or similar respirators account for a larger risk reduction than disposable surgical or other similar masks.[63] Masks are protective for both healthcare workers and people in communities exposed to infection; evidence supports masking in both healthcare and non-healthcare settings, with no striking differences detected in the effectiveness of masks between the settings.[63]
The CDC highlighted a number of studies in their 10 November 2020, scientific brief detailing the benefits of community masking.[142] In a study of 124 Beijing households with at least one laboratory-confirmed case of SARS-CoV-2 infection, mask use by the index patient and family contacts before the index patient developed symptoms reduced secondary transmission within the households by 79%.[163] A retrospective case-control study from Thailand documented that, among more than 1,000 people interviewed as part of contact tracing investigations, those who reported having always worn a mask during high-risk exposures experienced a greater than 70% reduced risk of acquiring infection compared with people who did not wear masks under these circumstances.[164] A similar study in three Western countries also came up with a 70% risk reduction.[165] Investigations involving infected passengers aboard flights longer than ten hours strongly suggest that masking prevented in-flight transmissions, as demonstrated by the absence of infection developing in other passengers and crew in the 14 days following exposure.[166] In addition, the CDC said the benefit of universal masking, including reductions in infections and mortality, has been demonstrated in community-level analyses by a set of studies involving the Massachusetts hospital system, the German city Jena, the American state Arizona, a panel of 15 American states and Washington, D.C., Canada nationally, and the United States nationally.[142]
In addition to studying the impact of mask-wearing on transmission in a community, direct studies can be done on whether a mask filters out virus-carrying particles from the air. In August 2021, a study of the fabric of masks worn in the community found that they filtered out between half and three-quarters of the viral RNA.[167] Respirators made to a standard such as N95 or FFP2 when properly fitted should filter out at least 95% of the virus.
Optimal face mask designs and use[edit]
A scientific review of research about the overall efficacy of face masks in terms of product design (such as thermal comfort and flow resistance) and ways of usage found that fluid dynamics and fabrication techniques have a significant impact on performance. According to the review, studies showed that cotton and surgical masks had a microorganism filtration efficiency of 86.4% and 99.9% respectively, while the surgical mask was three times more effective in blocking transmission than the cotton mask and could lead to a decrease of the effective reproduction number to below 1 – which could halt epidemic spread in a region where 70% of residents use them consistently in public.[168][169]
By January 2021, several lines of research recommended double-masking (wearing a cloth mask over a surgical mask, along with using a mask filter, or wearing a nylon covering over a mask) as being efficacious.[170]
Society and culture[edit]
Attitudes[edit]
In mid-2020 as the pandemic grew, the public interest in face masks as a means of protection was greatly increased,[246] often even before governments implemented mandatory mask-wearing.[247]
In East Asian societies, a primary reason for mask-wearing is to protect others from oneself.[248][249] The broad assumption behind the act is that anyone, including seemingly healthy people, can be a carrier of the coronavirus.[249] The usage of masks is seen as a collective responsibility to reduce the transmission of the virus.[250] A face mask is thus seen as a symbol of solidarity in Eastern countries.[250] Elsewhere, the need for mask-wearing is still often seen from an individual perspective where masks only serve to protect oneself.[248] In April 2020, a study comparing masking-related perceptions between China and three German speaking countries (Austria, Germany, and Switzerland) also showed that Chinese had stronger pro-masking perceptions than the European participants.[251] However, in 2020, people began promoting a new meaning of masking as an act of solidarity to each other.[252][141][253][254]