Protection against SARS-CoV-2 after Covid-19 vaccination and previous infection

V. Hall, S. Foulkes, F. Insalata, P. Kirwan, A. Saei, A. Atti, E. Wellington,, J. Khawam, K. Munro, M. Cole, C. Tranquillini, A. Taylor‑Kerr, N. Hettiarachchi, D. Calbraith, N. Sajedi, Iain Milligan, Y. Themistocleous, D. Corrigan, L. Cromey, L. PriceS. Stewart, E. de Lacy, C. Norman, E. Linley, A.D. Otter, A. Semper, J. Hewson, S. D’Arcangelo, M. Chand, C.S. Brown, T. Brooks, J. Islam, A. Charlett, S. Hopkins*, SIREN Study Group

*Corresponding author for this work

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BACKGROUND The 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. METHODS We 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. RESULTS Of 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. CONCLUSIONS Two 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.

Original languageEnglish
Pages (from-to)1207-1220
Number of pages14
JournalNew England Journal of Medicine
Issue number13
Early online date16 Feb 2022
Publication statusPublished - 31 Mar 2022


  • SARS-CoV-2
  • Covid-19 vaccination
  • prospective studies
  • adaptive immunity/immunology
  • COVID-19 Nucleic Acid Testing
  • humans
  • BNT162 vaccine/therapeutic use
  • ChAdOx1 nCoV-19/therapeutic use
  • United Kingdom
  • asymptomatic diseases
  • COVID-19 vaccines/immunology
  • COVID-19/diagnosis
  • vaccination/methods
  • vaccine efficacy
  • health personnel

ASJC Scopus subject areas

  • General Medicine


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