Breakthrough SARS-CoV-2 Infections after Vaccination in North Carolina
Importance: Real-world data are needed to assess incidence and factors associated with breakthrough SARS-CoV-2 infections following vaccination. Objective: Estimate incidence of breakthrough infections and assess associations with risk factors using self-reported data from a large NC population sample. Design: Prospective observational cohort study utilizing daily online survey data to capture information about COVID-19 symptoms, testing, and vaccination status. Setting: Six health care systems in North Carolina with data collected between January 15, 2021 and September 24, 2021. Participants: Adult study participants who reported full vaccination with a COVID-19 mRNA or J&J non-replicating viral vector vaccine (n = 16,020). Exposures: Potential community exposure to SARS-CoV-2. Main Outcome and Measures: Self-reported breakthrough infection. Results: SARS-CoV-2 infection after vaccination was self-reported in 1.9% of participants, with an incidence rate of 7.3 per 100,000 person-years. Younger age (45-64 vs. 18-44: HR (95% CI) = 0.65 (0.51-0.82); 65+ vs. 18-44: HR (95% CI) = 0.59 (0.39-0.90)), and vaccination with J&J Ad26.COV2.S were associated with a higher risk of breakthrough infection compared to vaccination with Pfizer BNT162b2 (Ad26.COV2.S vs. BNT162b2: HR (95% CI) = 2.23 (1.40-3.56)), while participants vaccinated with mRNA-1273 (mRNA-1273 vs. BNT162b2: HR (95% CI) = 0.69 (0.50-0.96) and those residing in urban counties experienced a lower rate of SARS-CoV-2 breakthrough infection compared with those from suburban (HR (95% CI) = 1.39 (1.01-1.90)) or rural (HR (95% CI) = 1.57 (1.16-2.11)) counties. There was no significant association between breakthrough infection and participant sex, race, healthcare worker status, prior COVID-19 infection, routine mask use, or overall vaccination rate in the county of residence. Conclusions and Relevance: This NC community-based observational study showed that the proportion of the cohort who self-report breakthrough SARS-CoV-2 infections was 7.3 events per 100,000 person-years. Younger adults, those vaccinated with J&J Ad26.COV2.S, and those residing in suburban or rural counties were at higher risk of breakthrough infections and should be targeted for additional risk mitigation strategies to decrease community transmission.