College Vaccine Mandates Reduced Local COVID Infections and Deaths
When colleges and universities reopened in the fall of 2021, only 47 percent of 18-to-24-year-olds in the United States were fully vaccinated against COVID-19. At institutions that required students to be vaccinated, however, the vaccination rates were much higher. In The Effect of Vaccine Mandates on Disease Spread: Evidence from College COVID-19 Mandates (NBER Working Paper 30303), Riley K. Acton, Wenjia Cao, Emily E. Cook, Scott A. Imberman, and Michael F. Lovenheim show that the health benefits of these vaccination requirements for college students extended to their local communities.
The researchers combine data on college vaccination policies and fall semester start dates from the College Crisis Initiative (C2i) with weekly county public health measures from the Centers for Disease Control and Prevention (CDC). They compare health outcomes in counties where colleges had a vaccination mandate to outcomes in counties where colleges did not, before and after fall 2021 semester start dates.
The first figure shows the differential change in infection rates in every week of the semester for counties where colleges mandated vaccination relative to counties where colleges did not. It shows that in the 11 weeks leading up to the fall semester, there were no differences between these counties after accounting for political leanings and pre-semester vaccination rates. But COVID case rates began to diverge in the week prior to the start of classes, when many students arrived on campus, and the gap persisted throughout the semester. The cumulative effect over the semester was 339 fewer COVID cases per 100,000 county residents (a 10 percent reduction) in counties where colleges required vaccination.
Cases in affected counties were lower for all age groups, not just among the college-aged population. That is, college vaccination mandates didn’t merely reduce on-campus infections, but reduced the spread of illness in the broader community.
The second figure shows a similar pattern for COVID death rates. Mortality diverged a few weeks after the semester started, consistent with typical lags between infections and fatalities. Over the entire semester, college vaccine requirements reduced deaths by 13 percent, preventing 5.4 deaths per 100,000 residents.
Of course, colleges that mandated vaccination differed from those that did not. For example, 95 percent of colleges that required vaccination implemented indoor mask mandates, whereas only 69 percent of colleges without vaccine mandates did. Similarly, 21 percent of colleges with vaccine mandates required COVID testing for students, compared to 4 percent of colleges without vaccine mandates. To address this concern about other differences between the colleges, the researchers conduct the same analysis for the fall of 2020 — when vaccines were not yet available, but other differences in college policies, such as mask mandates and testing, already existed. Counties with colleges that implemented a vaccine mandate in the fall of 2021 did not have any additional public health advantages in the fall of 2020.
Effects of vaccine mandates were stronger in counties with larger numbers of college students relative to the county population, and in counties where the college students had low predicted vaccination rates based on their demographic characteristics. These patterns provide additional validation that the estimates reflect the causal effect of the vaccination policy.