Effectiveness of public health measures in reducing the incidence of Covid-19
bmj.com
bmj.com
Bundgaard (not Bundagaard) 2021 [1]:
−0.3 percentage point (95% CI, −1.2 to 0.4 percentage point; P = 0.38) difference; statistically not significant. Limitations: “Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others.”
Doung-ngern 2020 [2]:
11% of control not tested; 59.2% of cases linked to boxing stadium; Persons who wore masks were also more likely to practice other measures [e.g. washing hands often (79% vs. 26% for those who did not wear a mask)]
Krishnamachari 2021 [3]:
Heavily confounded. States with no mask mandate had a 2.16x higher case rate, yet “stay at home orders and school closures had no significant influence”? No analysis of “restrictions on gatherings, closing of nonessential business and restaurant closures”?
Lio 2021 [4]:
Retrospective, internet questionnaire with 24 cases.
Wang 2020 [5]:
Telephone interview; Other than that, no issues imo.
Xu 2020 [6]:
“Despite the relatively large sample size, the total cases of COVID-19 infections were still small so that the relationship between NPIs and a COVID-19 infection should be confirmed by other larger epidemiological studies. Fifth, the potential risk compensating effects of wearing a mask against other NPIs should be considered as being of a hypothesis-generating nature given the potential limitations previously outlined. Sixth, all the information collected in the study was self-reported, which could have potential biases. Common to any observational studies with multiple outcomes and modeled with different effective sample sizes, the interpretations and generalization of the results should be strictly limited to the same setting and be aware of multiple tests risks”
- - -
Does it become significant, when we glue it all together? What about RCTs? [7]
"We included nine trials (of which eight were cluster‐RCTs) comparing medical/surgical masks versus no masks to prevent the spread of viral respiratory illness (two trials with healthcare workers and seven in the community). There is low certainty evidence from nine trials (3507 participants) that wearing a mask may make little or no difference to the outcome of influenza‐like illness (ILI) compared to not wearing a mask (risk ratio (RR) 0.99, 95% confidence interval (CI) 0.82 to 1.18)"
And the Bangladesh study? [8]
Is it enough for mask mandates?
[1] https://www.acpjournals.org/doi/10.7326/m20-6817
[2] https://wwwnc.cdc.gov/eid/article/26/11/20-3003_article
[3] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC7872858/
[4] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC8082215/
[5] https://gh.bmj.com/content/5/5/e002794?ijkey=69844ac74c8c8f6...
[6] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC7669364/
[7] https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD...