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Evidence that Masks Reduce Covid-19 Spread

Masks Prevent Many Respiratory Viruses

Animal Models Showing Masks Prevent Covid-19

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  • This study placed hamsters in separate cages and measured transmission of Covid-19 from an infected hamster to a healthy one. Surgical masks were shown to decrease infection rates. (Chan et al., 2020 doi: 10.1093/cid/ciaa644)

Mathmatical Models and Simulations Showing Masks Work

  • Mathematical modeling demonstrates mask ability to reduce transmission and mortality. It shows even masks of low efficacy can do this transmission rate is low or decreasing. (Eikenberry et al., 2020 doi: 10.1016/j.idm.2020.04.001)

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  • Mathematical modelling shows that higher quality face masks can protect the wearer from Covid-19, but two-way masking is better than one-way masking. (Bagheri et al., 2021 doi: 10.1073/pnas.2110117118)

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  • Researchers made a cough aerosol simulator to test how well different masks blocked the aerosol. N95 masks blocked 99%, surgical masks blocked 59%, cloth masks blocked 51% and face shields blocked only 2%. (Lindsly et al., 2021 doi: 10.1080/02786826.2020.1862409)

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  • Medical grade respirator masks are able to filter particles the size of Covid-19, while poorer quality masks are still able to filter larger aerosol particles which likely contain the virus. (Robinson et al., 2022 doi: 10.1080/02786826.2022.2042467)

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  • A model based on close-contact behaviour on the Subway showed that virus exposure could be reduced by 82% if all passengers wore surgical masks. (Liu et al, 2022 doi: 10.1016/j.jhazmat.2022.129233)

Masks Prevent Covid-19 in the Community

  • A study looking back at 124 households in Beijing found that when one family member had Covid-19, risk of secondary infections within the household decreased by 79% if the infected member started masking before symptoms. (Wang et al., 2020 doi: 10.1136/bmjgh-2020-00279)
     

  • In Hong Kong, in the period studied, masking compliance was 96.6% and Covid-19 incidence was significantly lower per million people than in countries with less mask compliance. (Cheng et al., 2020 doi: 10.1016/j.jinf.2020.04.024)
     

  • A study of 211 Covid-19 cases and 839 controls in Thailand showed that consistent mask wearing was independently associated with reduced risk of Covid-19 infection. (Doung-ngern et al., 2020 doi: 10.3201/eid2611.203003)
     

  • Introduction of mask mandates in states across the US was associated with a decline in Covid-19 infection growth rates. (Lyu and Wehby doi: 10.1377/hlthaff.2020.00818)
     

  • A randomised trial in nearly 350,000 people in Bangladesh found that mask wearing significantly reduced symptomatic Covid-19 infections. (Abaluck et al., 2021 doi: 10.1126/science.abi9069)
     

  • In US counties with masking mandates, daily case incidence declined by 35% in 6 weeks compared to matched counties without masking mandates. (Huang et al., 2022 doi: 10.1377/hlthaff.2021.01072)
     

  • An outbreak of Covid-19 on the USS Theodore Roosevelt, which carried 382 men, showed that those that wore face coverings were 70% less likely to become infected. (Payne et al., 2020 doi: 10.15585/mmwr.mm6923e4)   
     

  • A study of mask wearing in 20 million people, alongside Covid-19 infection data from 92 regions showed that mask wearing corresponds to a 19% reduction in Covid-19 reproductive number, R. (Leech et al., 2022 doi: 10.1073/pnas.2119266119)
     

  • Young children wearing masks was associated with a 13% reduction in risk of childcare program closure due to Covid-19, meaning more in-person education. (Murray et al., 2022 doi: 10.1001/jamanetworkopen.2021.41227)

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  • Every 10% rise in full masking by elementary school students, staff, and parents halved SARS-CoV-2 shedding detected in school wastewater, according to a direct observation of 10 schools in the San Diego area over 3 months in 2022 (Fielding-Miller R et al., 2023; 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 210)

Masks Prevent Covid-19 in Healthcare Settings

  • A hospital in Massachusetts managed to decrease rates of Covid-19 infection amongst 10,000 staff with universal masking, despite increasing rates of infection in the community. (Wang et al., 2020 doi: 10.1001/jama.2020.12897)
     

  • A North Carolina health provider showed that epidemiological curve of healthcare-aquired Covid-19 infections was flattened in healthcare workers following a universal masking policy. This was despite increasing community incidence. (Seidelman et al., 2020 doi: 0.1017/ice.2020.313)
     

  • A study of 29 general hospitals in Israel found that hospital-acquired Covid-19 infections among healthcare workers only started to decline following a universal masking mandate for all staff, patients and visitors. (Temkin et al., 2021 doi: 10.1017/ice.2021.207.Epub)
     

  • A systematic review of 13 studies in healthcare and the community found that probability of Covid-19 infection for mask wearers was 7%, compared with 52% for non-mask wearers. (Alihsan et al., 2022 doi: 10.1101/2022.07.28.22278153)
     

  • Properly fitted N95 masks alongside high quality air filtration can protect from Covid-19 infection for long periods, even with high viral loads at close range. (Landry et al., 2022 doi: 10.1093/infdis/jiac195)
     

  • This study shows masks were able to block the exhalation of virus particles by individuals infected by Covid-19 in Brazil. (Mello et al., 2022 doi: 10.1371/journal.pone.0264389)

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