Antibody responses after a single dose of ChAdOx1 nCoV-19 vaccine in healthcare workers previously infected with SARS-CoV-2

EBioMedicine. 2021 Aug;70:103523. doi: 10.1016/j.ebiom.2021.103523. Epub 2021 Aug 12.


Background: Recent reports demonstrate robust serological responses to a single dose of messenger RNA (mRNA) vaccines in individuals previously infected with SARS-CoV-2. Data on immune responses following a single-dose adenovirus-vectored vaccine expressing the SARS-CoV-2 spike protein (ChAdOx1 nCoV-19) in individuals with previous SARS-CoV-2 infection are however limited, and current guidelines recommend a two-dose regimen regardless of preexisting immunity.

Methods: We compared RBD-specific IgG and RBD-ACE2 blocking antibodies against SARS-CoV-2 wild type and variants of concern following two doses of the mRNA vaccine BNT162b2 in SARS-CoV-2 naïve healthcare workers (n=65) and a single dose of the adenovector vaccine ChAdOx1 nCoV-19 in 82 healthcare workers more than (n=45) and less than (n=37) 11 months post mild SARS-CoV-2 infection at time of vaccination.

Findings: The post-vaccine levels of RBD-specific IgG and neutralizing antibodies against the SARS-CoV-2 wild type and variants of concern including Delta lineage 1.617.2 were similar or higher in participants receiving a single dose of ChAdOx1 nCoV-19 vaccine post SARS-CoV-2 infection (both more than and less than 11 months post infection) compared to SARS-CoV-2 naïve participants who received two doses of BNT162b2 vaccine.

Interpretation: Our data support that a single dose ChAdOx1 nCoV-19 vaccine that is administered up to at least 11 months post SARS-CoV-2 infection serves as an effective immune booster. This provides a possible rationale for a single-dose vaccine regimen.

Funding: A full list of funding bodies that contributed to this study can be found in the Acknowledgements section.

Keywords: BNT162b2 vaccine; ChAdOx1 nCoV-19; Neutralizing antibody response; Prior infection; SARS-CoV-2.

MeSH terms

  • Adult
  • Antibodies, Neutralizing / immunology*
  • Antibody Formation / immunology*
  • BNT162 Vaccine
  • COVID-19 / immunology*
  • COVID-19 Vaccines / immunology*
  • ChAdOx1 nCoV-19
  • Female
  • Health Personnel
  • Humans
  • Immunization, Secondary / methods
  • Immunoglobulin G / immunology
  • Male
  • Middle Aged
  • SARS-CoV-2 / immunology*
  • Spike Glycoprotein, Coronavirus / immunology
  • Vaccination / methods


  • Antibodies, Neutralizing
  • COVID-19 Vaccines
  • Immunoglobulin G
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2
  • ChAdOx1 nCoV-19
  • BNT162 Vaccine