HMS Study Finds Mask-Wearing, Social Distancing Reduce Covid-19 Infections by 87% on College Campuses


Harvard Medical School researchers found that a combination of wearing masks and practicing social distancing can reduce student and faculty Covid-19 infections on college campuses by roughly 87 percent, according to a peer-reviewed study published last week.

The study, which was published on Dec. 21 in the Annals of Internal Medicine, used a dynamic microsimulation model to project the clinical and economic outcomes of different intervention strategies over the course of one semester, or 105 days.

Researchers measured outcomes by projected infections per 5,000 undergraduate students and 1,000 faculty in addition to days in isolation, test counts, test costs, costs per infection prevented, and cost per quality-adjusted life year, which incorporates health-related quality of life.

Of the 24 different infection control strategies the researchers modeled, adding routine testing to mandatory masking and social distancing prevented 96 percent of cases.


Lead author and Medical School professor Elena Losina said frequent testing comes at a higher cost per infection prevented. She said she does not believe cost is a “prohibitive factor” for Harvard, but it could be challenging for larger public universities and schools with lower budgets.

The study estimated program costs ranging from about $400,000 for minimal social distancing to up to $2.1 million for programs with Covid-19 testing. While extensive masking and social distancing cost $170 per infection prevented, adding routine testing ranges from about $2,000 to more than $17,000 per infection prevented.

The study comes as Harvard prepares to double the number of undergraduates living on campus this spring. Undergraduate case numbers remained low throughout the fall when only freshmen and students with challenging home environments lived on campus. The College invited seniors and most juniors to live in the dorms in the spring.

Losina said Harvard administrators have not contacted the researchers, but they would “be glad to chat with Harvard leadership.”

Losina also said she hopes the results of the study will motivate students to follow the University’s existing Covid-19 guidelines on mask-wearing, social distancing, and routine testing.

“I’m an optimist, so I think for the spring semester, it shows that masks and careful adherence to policies and recommendations that the University provides can be quite successful,” Losina said. “So hopefully this will equip and encourage students to follow the rules.”

Medical School instructor Pooyan Kazemian, who co-authored the study, wrote in an email that the study helped Case Western Reserve University administrators evaluate their Covid-19 campus protocols.

Losina said the researchers' model accounts for fatigue and the relaxation of guidelines over time as students become less willing to adhere to those measures. She said it was difficult, however, to track possible instances of transmission as students and faculty spend time participating in different activities.

Medical School professor Mathias D. Lichterfeld — who was not involved in the study — wrote in an email that the findings show non-pharmacological interventions such as masks and social distancing can reduce the spread of the virus before vaccines are distributed across campuses. The report does not account for contact tracing or vaccination as an intervention strategy.

“It’s remarkable that the combination of social distancing and mandatory masks can be almost as effective (87% in the paper) as vaccines (94-95%) for prevention — so following [non-pharmacological interventions] until vaccines are available is critical,” Lichterfeld wrote.

Medical School professor and study co-author Kenneth A. Freedberg ’79 wrote in an email that mask-wearing and social distancing trump routine testing in importance for curbing Covid-19 infection.

“Regular testing, as done at Harvard, can help further decrease infections, but it is less important on its own,” Freedberg wrote.

Still, he wrote that efforts to slow the spread of the virus in the United States have been limited by politics.

“The politicization of this virus in the US is responsible for much of the morbidity and mortality it has caused,” Freedberg wrote. “Hopefully we are now moving past that phase, on college campuses and throughout the country.”

—Staff writer Simon J. Levien can be reached at Follow him on Twitter @simonjlevien.

–Staff writer Meimei Xu can be reached at Follow her on Twitter @meimeixu7.