CHALLENGES IN ESTIMATING THE EFFECTIVENESS OF 2 DOSES OF COVID-19 VACCINE BEYOND 6 MONTHS IN ENGLAND

Understanding how the effectiveness of coronavirus disease 2019 (COVID-19) vaccine changes over time and in response to new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants is crucial to scheduling subsequent doses. In a previous study, Horne et al. (1) quantified vaccine effectiveness (VE) over 6 consecutive 4-week periods from 2 weeks to 26 weeks after the second dose. Waning of hazard ratios (HRs) when comparing vaccinated persons with unvaccinated persons was approximately log-linear over time and was consistent across COVID-19-related outcomes and risk-based subgroups. To investigate waning beyond 26 weeks and in the era of the Omicron variant, we extended follow-up to the earliest of 50 weeks after the second dose or March 31, 2022.

Automated summary

Understanding how the effectiveness of COVID-19 vaccines changes over time and in response to new variants is crucial for scheduling subsequent doses. Previous research has shown that vaccine effectiveness decreases in a log-linear manner over time and remains consistent across different risk-based subgroups. To further investigate the waning effectiveness beyond 26 weeks and in the era of the Omicron variant, the follow-up period was extended to the earliest of 50 weeks after the second dose or March 31, 2022.