Wearing a mask in health care settings had little, if any effect on the spread of the highly transmissible Omicron variant of COVID-19 among patients, according to British researchers.
During the COVID-19 pandemic, mask mandates for hospitals, clinics, and nursing homes became a staple of many countries’ attempts at curbing the spread of the virus. In the UK, all staff and visitors at health care facilities were required to wear splash-resistant surgical face masks until June 2022, after which individual hospitals could decide their own mask policies.
“A low-tech, low-cost intervention without well-established benefit was reasonable in the context of the early pandemic,” scientists at St. George’s Hospital in London said. “However, with a reduction in the severity of COVID-19 disease, in later variants, the risk-benefit balance becomes more questionable.”
For their study, the scientists analyzed routinely collected infection control data at St. George’s between Dec. 4, 2021, and Sept. 10, 2022—a 40-week period spanning from the first week when the Omicron variant became the country’s dominant cause of infection during the pandemic to the point when the British government ended pre-admission COVID-19 tests at hospitals. The Omicron variant was the dominant strain throughout this period.
During the first phase of the study, from Dec. 4, 2021, to June 1, 2022, all staff and visitors at St. George’s were required to wear surgical masks in both clinical and nonclinical areas of the hospital. In phase two, from June 1 to Sept. 10, 2022, the mask mandate only remained in place for staff working in certain high-risk wards, such as acute medical units and intensive care units.
When adjusting the hospital COVID-19 infection rate for the underlying community infection rate identified by pre-admission test results, researchers found no evidence that removing the mask mandate led to any “statistically significant change” in the rate of patients contracting the virus while in the hospital.
Moreover, the scientists emphasized that neither did they find any evidence of a “delayed effect,” noting that their analysis showed no change in the COVID-19 infection rate during phase two of the study. Even the group that continued wearing masks had no immediate or delayed change in infection rate.
“Requirements to wear surgical masks in a large London hospital during the first 10 months of Omicron activity made no discernible difference to reducing hospital-acquired SARS-CoV-2 infections,” they concluded.
Dr. Aodhan Breathnach, the study’s senior author and a medical microbiologist at St. George’s, said in a statement: “Many hospitals have retained masking at significant financial and environment cost and despite the substantial barrier to communication. We hope this empirical evidence can help inform a rational and proportionate mask policy in health services.”
The authors did acknowledge some limitations of the study, such as that they didn’t examine to what extent hospital staff actually adhered to the mask policy and that they were unable to determine infection rates among staff. They also highlighted the fact that the study is observational in nature and can’t prove causation.
The study will be presented as an abstract at the 2023 European Congress of Clinical Microbiology & Infectious Diseases in Copenhagen, Denmark, from April 15 to 18.
