Immune Responses in Fully Vaccinated Individuals Following Breakthrough Infection with the SARS-CoV-2 Delta Variant in Provincetown, Massachusetts

Collier, A.-r.; Brown, C.; McMahan, K.; Yu, J.; Liu, J.; Jacob-Dolan, C.; Chandrashekar, A.; Tierney, D.; Ansel, J.; Rowe, M.; Sellers, D.; Ahmad, K.; Aguayo, R.; Anioke, T.; Gardner, S.; Siamatu, M.; Bermudez Rivera, L.; Hacker, M.; Madoff, L.; Barouch, D.

Background A cluster of over a thousand infections with the SARS-CoV-2 delta variant was identified in a predominantly fully vaccinated population in Provincetown, Massachusetts in July 2021. Immune responses in breakthrough infections with the SARS-CoV-2 delta variant remain to be defined. Methods Humoral and cellular immune responses were assessed in 35 vaccinated individuals who were tested for SARS-CoV-2 in the Massachusetts Department of Public Health outbreak investigation. Results Vaccinated individuals who tested positive for SARS-CoV-2 demonstrated substantially higher antibody responses than vaccinated individuals who tested negative for SARS-CoV-2, including 28-fold higher binding antibody titers and 34-fold higher neutralizing antibody titers against the SARS-CoV-2 delta variant. Vaccinated individuals who tested positive also showed 4.4-fold higher Spike-specific CD8+ T cell responses against the SARS-CoV-2 delta variant than vaccinated individuals who tested negative. Conclusions Fully vaccinated individuals developed robust anamnestic antibody and T cell responses following infection with the SARS-CoV-2 delta variant. These data suggest important immunologic benefits of vaccination in the context of breakthrough infections.