On March 28, 2020, as COVID-19 cases began to shut down public life in much of the United States, then-Surgeon General Jerome Adams issued an advisory on Twitter: The general public should not wear masks. “There is scant or conflicting evidence they benefit individual wearers in a meaningful way,” he wrote.
Adams’ advice was in line with messages from other US officials and the World Health Organization. Days later, though, US public health leaders shifted course. Mask-wearing was soon a pandemic-control strategy worldwide, but whether this strategy succeeded is now a matter of heated debate—particularly after a major new analysis, released in January, seemed to conclude that masks remain an unproven strategy for curbing transmission of COVID-19 and other respiratory viruses.
“There’s still no evidence that masks are effective during a pandemic,” the study’s lead author, physician, and epidemiologist Tom Jefferson, recently told an interviewer.
Many public health experts vigorously disagree with that claim, but the study has caught attention, in part, because of its pedigree: It was published by Cochrane, a not-for-profit that aims to bring rigorous scientific evidence more squarely into the practice of medicine. The group’s highly regarded systematic reviews affect clinical practice worldwide. “It’s really our gold standard for evidence-based medicine,” said Jeanne Noble, a physician and associate professor of emergency medicine at the University of California, San Francisco. One epidemiologist described Cochrane as “the Bible.”
The new review, “Physical interventions to interrupt or reduce the spread of respiratory viruses,” is an updated version of a paper published in the fall of 2020. It dropped at a time when debates over COVID-19 are still simmering among scientists, politicians, and the broader public.
For some, the Cochrane review provided vindication. “Mask mandates were a bust,” conservative columnist Bret Stephens wrote in The New York Times last week. “Those skeptics who were furiously mocked as cranks and occasionally censored as ‘misinformers’ for opposing mandates were right.”