Incidence of positive SARS-CoV-2 PCR after COVID-19 vaccination with up to eight months of follow-up: Real life data from the Capital Region of Denmark

Background COVID-19 vaccines are implemented worldwide in efforts to curb the pandemic. This study investigates the risk of a positive SARS-CoV-2 RT-PCR test following BNT162b2 vaccination in a large real-life population in Denmark. Methods Vaccination status and positive SARS-CoV-2 RT-PCR results from adults in the Capital Region of Denmark (n=1,549,488) were obtained from national registries. PCR testing was free and widely available. The number of positive PCR tests per individual at risk were calculated as weekly rates. Time to positive PCR test was modelled using Kaplan-Meier methods and hazard ratios (HR) were calculated using Cox regression. Results 1,119,574 individuals received first dose of BNT162b2 and 1,088,879 received a second dose of BNT162b2. Individuals were followed up to 8.7 months after first dose (median: 5.5 months, IQR:4.1-8.7). Rates of PCR-confirmed SARS-CoV-2 infection two to four months after the second dose were 0.21, 0.33 and 0.36 per 1000 individuals per week at risk for July, August and September, respectively. Four or more months after the second dose, the rates were 0.56, 0.76 and 0.53 per 1000 individuals per week at risk for July, August and September, respectively. HR of SARS-CoV-2 infection after the second dose was 0.2 (95% CI: 0.05-0.48, p=0.001) for individuals with eight months follow-up. Conclusion Individuals who received two doses of the BNT162b2 COVID-19 vaccine had a low risk of breakthrough-infection after up to 8 months of follow-up. However, there was a tendency towards higher rates with longer follow-up.