New Study Finds Universal Masking Lowers Incidence of COVID-19 for Mass. Healthcare Workers
CAMBRIDGE, Mass. – Along with handwashing and physical distancing, the appropriate use of masks has been one of the essential pillars of infection prevention measures against COVID-19. However, rigorous evidence of masks’ effectiveness in blocking the transmission of COVID-19 pandemic has been limited. New research provides additional evidence of the benefits of universal masking in the healthcare setting. The study, published today by Occupational Medicine, found that universal masking at a Massachusetts healthcare system led to a flattening followed by a decrease in the COVID-19 epidemic curve among healthcare workers while the infection rate continued to steeply rise in the surrounding community population.
Existing evidence of the efficacy of universal masking among healthcare workers (HCWs) is largely based on self-comparison results (e.g., comparing pre- and post-masking phases). Researchers at Cambridge Health Alliance, a Harvard-affiliated community health system, and the Harvard University T.H. Chan School of Public Health, conducted the study at CHA to explore the effect of universal masking at the health system and used the statewide population as a comparison or reference group.
The investigators compared the COVID-19 incidence rates between CHA and Massachusetts residents. The study period was from March 17 (the date of the first COVID-19 positive incident in the healthcare system) to May 6 (the date Massachusetts implemented public masking). CHA implemented universal masking on March 26, and peak COVID-19 incidence in Massachusetts was April 20. The researchers categorized March 17-31 as the pre-intervention phase (allowing a 5-day lag from the masking policy to account for the average COVID-19 incubation period), April 1-20 the intervention phase, and April 21-May 6 the epidemic decline post-intervention phase. Temporal incidence trends were compared as the slopes of epidemic curves using 7-day averaged infection rates and compared using statistical models (standardized coefficients from linear regression models).
The study showed that after implementing universal masking during the phase of rising infections in both the healthcare system and the community, HCW infections sharply decreased, while community infections continued to rise until the state’s epidemic peak. Before the intervention, standardized infection rates showed almost identical increasing curves for the healthcare system and statewide population. During the intervention phase, the healthcare system’s epidemic slope became negative (standardized β: -0.68, 95% CI: -1.06 – -0.31), while Massachusetts’ slope remained positive (standardized β: 0.99, 95% CI: 0.94 – 1.05). Once the epidemic peaked on April 20, the both curves declined at similar rates.
“We found clear benefits to universal masking for preventing infectious spread within the work environment,” said study senior author Stefanos N. Kales, MD, MPH, division chief of occupational and environmental medicine at CHA and a professor at both Harvard Medical School and Harvard T.H. Chan School of Public Health. “Our findings suggest that universal masking policy should be implemented and maintained in healthcare settings as well as within indoor businesses when physical distancing and ventilation may be inadequate.”