Abstract
Background
During August–September 2021, a Connecticut college experienced a large SARS-CoV-2 Delta outbreak despite high (99%) vaccination coverage, indoor masking policies, and twice weekly reverse transcription-polymerase chain reaction (RT-PCR) testing. The Connecticut Department of Public Health investigated characteristics associated with infection and phylogenetic relationships among cases.
Methods
A case was a SARS-CoV-2 infection diagnosed by RT-PCR or antigen test during August–September 2021 in a student. College staff provided enrollment data, case information, and class rosters. An anonymous online student survey collected demographics, SARS-CoV-2 case and vaccination history, and activities the weekend before the outbreak. Multivariate logistic regression identified characteristics associated with infection. Phylogenetic analyses compared 115 student viral genome sequences with contemporaneous community genomes.
Results
Overall, 199/1788 students (11%) had lab-confirmed SARS-CoV-2 infection; most were fully vaccinated (194/199, 97%). Attack rates were highest among sophomores (72/414, 17%) and unvaccinated students (5/18, 28%). Attending in-person classes with an infectious student was not associated with infection (adjusted odds ratio [aOR] 1.0; 95%CI 0.5–2.2). Compared with uninfected students, students reporting an infection were more likely sophomores (aOR 3.3; 95%CI 1.1–10.7), attended parties/gatherings before the outbreak (aOR 2.8; 95%CI 1.3–6.4), and completed a vaccine series ≥180 days prior (aOR 5.5; 95%CI 1.8–16.2). Phylogenetic analyses suggested most cases derived from a common viral source.
Conclusions
This college SARS-CoV-2 outbreak occurred in a highly vaccinated population with prevention strategies in place. Infection was associated with unmasked off-campus parties/gatherings, not in-person classes. Students should stay up-to-date on vaccination to reduce infection.
Keywords: COVID-19, Delta, SARS-CoV-2 transmission, higher education, vaccine breakthrough
Contributor Information
Stephen M. Bart, Epidemic Intelligence Service, CDC, Atlanta, Georgia, USA; Connecticut Department of Public Health, Hartford, Connecticut, USA.
Christina C. Curtiss, Connecticut College, New London, Connecticut, USA.
Rebecca Earnest, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
Rachel Lobe-Costonis, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
Hanna Peterson, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
Caroline McWilliams, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
Kendall Billig, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
James L. Hadler, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA.
Nathan D. Grubaugh, Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA; Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, USA.
Victor J. Arcelus, Connecticut College, New London, Connecticut, USA.
Lynn E. Sosa, Connecticut Department of Public Health, Hartford, Connecticut, USA.
Supplementary Material
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