Evolution of long-term vaccine-induced and hybrid immunity in healthcare workers after different COVID-19 vaccine regimens

Med. 2023 Mar 10;4(3):191-215.e9. doi: 10.1016/j.medj.2023.02.004. Epub 2023 Feb 16.

Abstract

Background: Both infection and vaccination, alone or in combination, generate antibody and T cell responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the maintenance of such responses-and hence protection from disease-requires careful characterization. In a large prospective study of UK healthcare workers (HCWs) (Protective Immunity from T Cells in Healthcare Workers [PITCH], within the larger SARS-CoV-2 Immunity and Reinfection Evaluation [SIREN] study), we previously observed that prior infection strongly affected subsequent cellular and humoral immunity induced after long and short dosing intervals of BNT162b2 (Pfizer/BioNTech) vaccination.

Methods: Here, we report longer follow-up of 684 HCWs in this cohort over 6-9 months following two doses of BNT162b2 or AZD1222 (Oxford/AstraZeneca) vaccination and up to 6 months following a subsequent mRNA booster vaccination.

Findings: We make three observations: first, the dynamics of humoral and cellular responses differ; binding and neutralizing antibodies declined, whereas T and memory B cell responses were maintained after the second vaccine dose. Second, vaccine boosting restored immunoglobulin (Ig) G levels; broadened neutralizing activity against variants of concern, including Omicron BA.1, BA.2, and BA.5; and boosted T cell responses above the 6-month level after dose 2. Third, prior infection maintained its impact driving larger and broader T cell responses compared with never-infected people, a feature maintained until 6 months after the third dose.

Conclusions: Broadly cross-reactive T cell responses are well maintained over time-especially in those with combined vaccine and infection-induced immunity ("hybrid" immunity)-and may contribute to continued protection against severe disease.

Funding: Department for Health and Social Care, Medical Research Council.

Keywords: COVID vaccine; COVID-19; SARS-CoV-2; T cells; Translation to population health; antibody; immunity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antibodies, Neutralizing
  • BNT162 Vaccine
  • COVID-19 Vaccines
  • COVID-19*
  • ChAdOx1 nCoV-19
  • Health Personnel
  • Humans
  • Immunity, Humoral
  • Prospective Studies
  • SARS-CoV-2
  • Vaccines*

Substances

  • COVID-19 Vaccines
  • BNT162 Vaccine
  • ChAdOx1 nCoV-19
  • Vaccines
  • Antibodies, Neutralizing