A research letter yesterday in JAMA Network Open ties large gatherings of unvaccinated students and nonstudents at US universities during last spring's National Collegiate Athletic Association (NCAA) March Madness basketball tournament to COVID-19 outbreaks in the surrounding community.
Ashley L. O'Donoghue, PhD, at Beth Israel Deaconess Medical Center in Boston, conducted a difference-in-differences analysis to compare COVID-19 infection rates in counties surrounding the 64 universities that competed in the mid-March 2021 NCAA Men's Division I Basketball Tournament with counties in the same states with universities that were not competing.
At that time, new infections in counties with both competing and noncompeting universities were in decline, although SARS-CoV-2 variants were spreading quickly. Also, COVID-19 vaccination rates among young people were low because shots were being prioritized for older people and those at high risk for poor outcomes.
O'Donoghue derived county-level COVID-19 infection data from the New York Times from Jan 28 to May 25, 50 days before and after the tournament. Because celebrations tend to get bigger later in the tournament, the date of a team's last game was counted as the date of exposure to the virus.
Infections spiked 24 days after last game
Relative to counties with noncompeting universities, the estimated number of new COVID-19 infections in counties with competing universities rose significantly starting 8 days after the last game of tournament participation (13.4%; 95% confidence interval [CI], 0.8% to 25.9%).
Infection rates peaked 24 days after the last game (21.8%; 95% CI, 6.4% to 37.3%) and then fell until day 30, when the difference between participating and nonparticipating counties was no longer significant (17.1%; 95% CI, –0.6% to 34.7%).
"The findings of this cross-sectional study suggest that social gatherings among unvaccinated students were associated with increased COVID-19 infections (in this scenario, slowing the previous downward trend and briefly increasing) in a university's community beginning 8 days after the event, which corresponds with the 75th percentile of time to symptom onset," she wrote.
The researcher cautioned that states vary in how they test for and report COVID-19 infections and that universities competing in March Madness may have increased surveillance testing during and after the tournament, leading to higher case counts than in other counties.
"This study identifies an urgent gap in evidence on the risk of COVID-19 spread at social gatherings among university students, although the increase in transmission was brief," she wrote. "This increase in transmission may have been brief because of increases in the vaccination rate of university students during this time or because some students may have completed their semester before the end of the study period."
In a Beth Israel press release, O'Donoghue added that understanding the role of university social gatherings in community COVID-19 transmission has important implications for universities debating infection-prevention and control strategies.
"This suggests that vaccinations, surveillance testing of unvaccinated students, or other mitigation measures, are still important to reduce the spread of COVID-19 in a university's community," she said.