Summary of COVID-19 masks studies
1. Bundgaard et al., Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers
4,862 patient masks prophylaxis RCT: 18% fewer cases (p=0.33).RCT 4,862 community-dwelling adults in Denmark, showig no significant difference in COVID-19 cases with recommending the use of surgical masks outside the home. The prespecified mortality outcomes are not reported and the only severity information provided is symptom counts.
Nov 2020, Annals of Internal Medicine , https://www.acpjournals.org/doi/10.7326/M20-6817, https://c19p.org/bundgaard
2. Abaluck et al., Impact of community masking on COVID-19: A cluster-randomized trial in Bangladesh
342,183 patient masks prophylaxis RCT: 9% fewer symptomatic cases (p=0.05).RCT 342,183 adults in Bangladesh showing lower COVID-19 cases with a community-level mask promotion and distribution intervention. However, Recht [archives.argmin.net] shows that purple cloth masks had 0% efficacy, while red cloth masks were more effective than surgical masks, i.e., changing the color of the mask produced dramatically different outcomes. With a lack of biological plausibility, this difference suggests that the analytical approach used is not reliable enough for the effect size reported. The overall study found a very small absolute difference with 1,106 vs 1,086 symptomatic seropositive patients among those consenting to blood draws - a difference of only 20 people. Random variation and confounding issues may account for the entire effect seen. The most important outcomes were not reported. The pre-analysis plan shows hospitalization and mortality as outcomes. Appendix P states "we did not collect follow-up hospitalization and mortality data due to the..
Jan 2022, Science, https://www.science.org/doi/10.1126/science.abi9069, https://c19p.org/abaluck
3. Solberg et al., Personal protective effect of wearing surgical face masks in public spaces on self-reported respiratory symptoms in adults: pragmatic randomised superiority trial
3,801 patient masks prophylaxis RCT: 7% more cases (p=0.82).RCT 4,575 adults in Norway showing no significant difference in reported COVID-19 cases with surgical face mask use in public spaces. The study reports lower risk of overall respiratory infections, however this may be due to reporting bias - many more patients did not report data in the intervention arm, and the intervention appeared to be much more successful in patients with the belief that masks reduce infection (Figure 2), i.e., patients in the mask group that believe masks work may be less likely to report failure of their belief. In theory, if the missing data for intervention patients is more likely to show infection, imputation using the baseline predictors would adjust the odds ratio upward, however only mask belief shows a significant association with the outcome, and the analysis cannot distinguish between an actual association and reporting bias.
Jul 2024, BMJ, https://www.bmj.com/lookup/doi/10.1136/bmj-2023-078918, https://c19p.org/solberg
245 patient masks prophylaxis RCT: 98% more cases (p=0.06) and 164% worse results (p=0.08).
Cluster RCT 81 index cases and 245 household contacts in South Africa, showing no significant difference in COVID-19 cases with PPE use. The only symptom information is reported for index cases in the registry under adverse events. Publication was delayed for close to 3 years without explanation. Results were submitted to clinicaltrials.gov in 2022 but not made available until 2024.
Jul 2024, BMC Public Health, https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-024-19462-1, https://c19p.org/smith4
