Elapsed time since BNT162b2 vaccine and risk of SARS-CoV-2 infection in a large cohort

Israel, Ariel; Merzon, Eugene; Schäffer, Alejandro A.; Shenhar, Yotam; Green, Ilan; Golan-Cohen, Avivit; Ruppin, Eytan; Magen, Eli; Vinker, Shlomo

IMPORTANCE: Israel was among the first countries to launch a large-scale COVID-19 vaccination campaign, and quickly vaccinated its population, achieving early control over the spread of the virus. However, the number of COVID-19 cases is now rapidly increasing, which may indicate that vaccine protection decreases over time. OBJECTIVE: To determine whether time elapsed since the second BNT162b2 messenger RNA (mRNA) vaccine (Pfizer-BioNTech) injection is significantly associated with the risk of post-vaccination COVID-19 infection. DESIGN: This is a retrospective cohort study performed in a large state-mandated health care organization in Israel. PARTICIPANTS: All fully vaccinated adults who have received a RT-PCR test between May 15, 2021 and July 26, 2021, at least two weeks after their second vaccine injection were included. Patients with a history of past COVID-19 infection were excluded. MAIN OUTCOME AND MEASURE: Positive result for the RT-PCR test. RESULTS: The cohort included 33,993 fully vaccinated adults, 49% women, with a mean age of 47 years (SD, 17 years), who received an RT-PCR test for SARS-CoV-2 during the study period. The median time between the second dose of the vaccine and the RT-PCR test was 146 days, interquartile range [121–167] days. 608 (1.8%) patients had positive test results. There was a significantly higher rate of positive results among patients who received their second vaccine dose at least 146 days before the RT-PCR test compared to patients who have received their vaccine less than 146 days before: odds ratio for infection was 3.00 for patients aged over 60 (95% CI 1.86–5.11); 2.29 for patients aged between 40 and 59 (95% CI 1.67–3.17); and 1.74 for patients aged between 18 and 39 (95% CI 1.27–2.37); P<0.001 in each age group. CONCLUSIONS AND RELEVANCE: In this large population study of patients tested for SARS-CoV-2 by RT-PCR following two doses of mRNA BNT162b2 vaccine, we observe a significant increase of the risk of infection in individuals who received their last vaccine dose since at least 146 days ago, particularly among patients older than 60.