Masterpost on Mask Efficacy Reseach in Covid-19
Sick of hearing that masks don’t work? Me too :)))) here’s some research studies showing that they do for next time Karen starts Karening.
(Correct as of August 2022)
A general respiratory viruses review (there are many more but that’s a post for another day):
A review of studies showing mask wearing prevents respiratory virus transmission including SARS, influenza, bird flu and Covid-19.
Wang et al., 2021 doi: 10.1002/mds3.10163
Animal models and masks with Covid-19
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
Mathematical models/simulations and masks with Covid-19
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
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
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
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
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
Community settings and masks with Covid-19
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.
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
Healthcare settings and masks with Covid-19
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
“But masks can harbour bacteria and fungi and give you pneumonia”
This is most likely referring to the study by Park et al., 2022 doi: 10.1038/s41598-022-15409-x
However, if they actually read the paper they would find that:
Most fungi found were on the outside of the mask. Most fungi were opportunistic pathogens (only a danger to immunocompromised), rather than pathogenic.
Most bacteria were non-pathogenic in humans. Of the bacteria that were potentially pathogenic, most were commensal (normally found within the body) or opportunistic (don’t cause harm unless immunocompromised).
The article does not recommend against mask use, only repeated use of the same mask in immunocompromised individuals.
The paper points out that masks reduce transmission of Covid-19.
The paper points out that pathogenic bacteria and fungi are detectable on many materials we use in daily life.
And if you’re really worried about what’s on your mask:
Masks can be sterilized with steam or hot water without compromising their efficacy.
Rahman et al., 2022 doi: 10.3390/polym14071296
“But studies show that masks don’t work”
The most commonly cited evidence of this is a Danish study on the effectiveness of adding a mask mandate.
Bundgaard et al., 2021 doi: 10.7326/M20-6817
This study found that there was no significant difference in infection rates in 4000 Danes, between those recommended masks and those not recommended masks.
However, the study has many limitations which may explain why results differ from the majority of mask studies:
Infection rates reported in the study were not comparable with rates reported in the Danish population at the time.
Fewer people were infected in the masked group, but not to a level of statistical significance. The authors state that results are inconclusive, as opposed to concluding that masks provide no protection.
Only surgical masks were given to participants, which have a limited ability to protect the wearer from airborne viruses vs aerosolised viruses due to their loose fit.
The study only assessed how effectively the masks protected the wearer, not how well it reduced transmission to others.
In the group where masks were recommended, only 46% reported wearing their masks completely as recommended. I.e. more than half of this group did not always wear a mask.
The authors themselves state that the findings should not be used to conclude that mask recommendations in the community would not be effective in controlling Covid-19 spread.
“But masks make it hard to communicate!”
Data is mixed on expression recognition, but some studies show masks have no detrimental effect. Also, context and additional non-verbal cues are often not considered in studies.
A study of children aged 7-13 found that face masks did not impair ability to infer emotions.
Ruba and Pollack, 2020 doi: 10.1371/journal.pone.0243708
Also, clear face masks are available, including clear surgical masks and clear respirators.
“But masks reduce oxygenation”
Wearing a face mask does not cause low O2 nor high CO2 at rest or during activity.
Shein et al., 2021 doi: 10.1371/journal.pone.0247414
Gas exchange is not significantly affected by the use of surgical mask, even in subjects with severe lung impairment.
Samannan et al., 2020 doi: 10.1513/AnnalsATS.202007-812RL
THAT graph that anti-maskers love to show
“Fig. 3. Correlation between Infection Rate and Annual Mask Usage generated from discarded face masks. (USA: United States of America; UK: United Kingdom)”
This graph actually comes from a paper on microplastics from face mask disposal, as opposed to anything epidemiological.
Shukla et al., 2022 doi: 10.1016/j.chemosphere.2022.134805
This graph does not accurately show the Annual Mask Usage (AMU) of each country to an accuracy that could ever be used in a paper with an epidemiological focus.
The authors did not account for variable mask usage in different countries and they use no real world data used on this. Instead, variation in Annual Mask Usage (AMU) is estimated by considering the population of each country in rural vs urban areas, and the presumed acceptance of masks in each area, which is constant for each country (10% in rural areas vs 80% in urban). Basically, this graph shows no accurate data on mask wearing in each country.
The authors also state that there is a correlation between AMU and infection rate. However, the country with the greatest population in the world, China, counters this trend. Equally, the data for India and Brazil, which also have a large proportion of the global population, also contradict this conclusion. This would explain why the authors never attempted to provide statistical tests to prove the correlation that they have supposedly found.
I think that about sums it up, but feel free to add more!
