Do mask wearing, physical distancing, handwashing really protect against COVID-19?

Handwashing, mask wearing, and physical distancing effectively reduce the transmission of SARS-CoV-2 and the incidence of COVID-19, suggest the results of a systematic review and meta-analysis.

“Some of the public health measures seem to be more stringent than others and have a greater impact on economies and the health of populations,” the researchers said.

“When implementing public health measures, it is important to consider specific health and sociocultural needs of the communities and to weigh the potential negative effects of the public health measures against the positive effects for general populations,” they added.

The databases of Medline, Embase, CINAHL, Biosis, Joanna Briggs, Global Health, and World Health Organization were searched for observational and interventional studies assessing the effectiveness of public health measures in reducing the incidence of COVID-19, SARS-CoV-2 transmission, and death.

The researchers performed DerSimonian Laird random effects meta-analysis to examine the effect of mask wearing, handwashing, and physical distancing measures on the incidence of COVID-19. They also computed pooled effect estimates and assessed heterogeneity using Cochran’s Q test and the I² metrics, with two tailed P values.

Of the 72 studies that met the eligibility criteria, 35 evaluated individual public health measures and 37 assessed multiple public health measures as a “package of interventions.” [BMJ 2021;375:e068302]

Eight of the 35 studies were included in the meta-analysis and indicated a decrease in COVID-19 incidence associated with handwashing (relative risk [RR], 0.47, 95 percent confidence interval [CI], 0.19–1.12; I²=12 percent), mask wearing (RR, 0.47, 95 percent CI, 0.29–0.75; I²=84 percent), and physical distancing (RR, 0.75, 95 percent CI, 0.59–0.95; I²=87 percent).

Meta-analysis was not possible for such outcomes as quarantine and isolation, universal lockdowns, and closures of borders, schools, and workplaces due to heterogeneity of the studies. The effects of these interventions were descriptively synthesized instead.

“The effectiveness of measures such as universal lockdowns and closures of businesses and schools for the containment of COVID-19 have largely been effective but depended on early implementation when incidence rates of COVID-19 were still low,” the researchers said. [Cad Saude Publica 2020;36:e00213920; Appl Health Econ Health Policy 2020;18:509-17; BMC Public Health 2021;21:965]

“Only Japan reported no decrease in COVID-19 incidence after school closures, and other studies found that different public health measures were sometimes implemented simultaneously or soon after one another, thus the results should be interpreted with caution,” they noted. [Int J Infect Dis 2020;99:57-61; Proc Natl Acad Sci U S A 2021;118:e2020834118; S Afr Med J 2020;110:1119-1123]

Previous literature reviews also found mask wearing effective in containing SARS-CoV-2, but more high-level evidence was needed to provide unequivocal support for the effectiveness of universal use of face masks. [Proc Natl Acad Sci U S A 2021;118:e2014564118; Euro Surveill 2020;25:2000725; Cien Saude Colet 2020;25:3365-3376]

In addition, most studies assessing mask wearing were prone to confounding bias, which might have influenced the conclusions drawn from the current review: effect estimates might have been under- or overestimated or could be related to other measures in place at the time the studies were conducted.

“Further research is needed to assess the effectiveness of public health measures after adequate vaccination coverage has been achieved,” the researchers said. “It is likely that further control of the COVID-19 pandemic depends not only on high vaccination coverage and its effectiveness but also on ongoing adherence to effective and sustainable public health measures.”