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BackgroundThe duration and effectiveness of immunity from infection with and vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are relevant to pandemic policy interventions, including the timing of vaccine boosters.MethodsWe investigated the duration and effectiveness of immunity in a prospective cohort of asymptomatic health care workers in the United Kingdom who underwent routine polymerase-chain-reaction (PCR) testing. Vaccine effectiveness (≤10 months after the first dose of vaccine) and infection-acquired immunity were assessed by comparing the time to PCR-confirmed infection in vaccinated persons with that in unvaccinated persons, stratified according to previous infection status. We used a Cox regression model with adjustment for previous SARS-CoV-2 infection status, vaccine type and dosing interval, demographic characteristics, and workplace exposure to SARS-CoV-2.ResultsOf 35,768 participants, 27% (9488) had a previous SARS-CoV-2 infection. Vaccine coverage was high: 95% of the participants had received two doses (78% had received BNT162b2 vaccine [Pfizer-BioNTech] with a long interval between doses, 9% BNT162b2 vaccine with a short interval between doses, and 8% ChAdOx1 nCoV-19 vaccine [AstraZeneca]). Between December 7, 2020, and September 21, 2021, a total of 2747 primary infections and 210 reinfections were observed. Among previously uninfected participants who received long-interval BNT162b2 vaccine, adjusted vaccine effectiveness decreased from 85% (95% confidence interval [CI], 72 to 92) 14 to 73 days after the second dose to 51% (95% CI, 22 to 69) at a median of 201 days (interquartile range, 197 to 205) after the second dose; this effectiveness did not differ significantly between the long-interval and short-interval BNT162b2 vaccine recipients. At 14 to 73 days after the second dose, adjusted vaccine effectiveness among ChAdOx1 nCoV-19 vaccine recipients was 58% (95% CI, 23 to 77) - considerably lower than that among BNT162b2 vaccine recipients. Infection-acquired immunity waned after 1 year in unvaccinated participants but remained consistently higher than 90% in those who were subsequently vaccinated, even in persons infected more than 18 months previously.ConclusionsTwo doses of BNT162b2 vaccine were associated with high short-term protection against SARS-CoV-2 infection; this protection waned considerably after 6 months. Infection-acquired immunity boosted with vaccination remained high more than 1 year after infection. (Funded by the U.K. Health Security Agency and others; ISRCTN Registry number, ISRCTN11041050.).

Original publication




Journal article


The New England journal of medicine

Publication Date





1207 - 1220


From the U.K. Health Security Agency (V.H., S.F., F.I., P.K., A. Saei, A.A., E.W., J.K., K.M., M. Cole, C.T., A.T.-K., N.H., D. Calbraith, N.S., I.M., Y.T., E. Linley, A.D.O., A. Semper, J.H., S.D., M. Chand, C.S.B., T.B., J.I., A.C., S.H.), Guy's and St. Thomas' NHS Foundation Trust (M. Chand), and the National Institute for Health Research (NIHR) Health Protection Research Unit in Vaccines and Immunisation, London School of Hygiene and Tropical Medicine, in partnership with Public Health England (A.C.), London, the Health Protection Research NIHR Unit in Healthcare Associated Infections and Antimicrobial Resistance, University of Oxford, Oxford (V.H., C.S.B., S.H.), the Medical Research Council Biostatistics Unit, University of Cambridge, Cambridge (P.K.), the Public Health Agency Northern Ireland, Belfast (D. Corrigan, L.C.), Glasgow Caledonian University and Public Health Scotland, Glasgow (L.P., S.S.), Public Health Wales (E. Lacy) and Health and Care Research Wales (C.N.), Cardiff, and the NIHR Health Protection Research Unit in Behavioural Science and Evaluation, University of Bristol, in partnership with Public Health England, Bristol (A.C.) - all in the United Kingdom.


SIREN Study Group, Humans, Vaccination, Prospective Studies, Health Personnel, Adaptive Immunity, Asymptomatic Diseases, United Kingdom, COVID-19, SARS-CoV-2, COVID-19 Vaccines, COVID-19 Nucleic Acid Testing, Vaccine Efficacy, BNT162 Vaccine, ChAdOx1 nCoV-19