Quantitative SARS-CoV-2 anti-spike responses to Pfizer-BioNTech and Oxford-AstraZeneca vaccines by previous infection status

Clin Microbiol Infect. 2021 Oct;27(10):1516.e7-1516.e14. doi: 10.1016/j.cmi.2021.05.041. Epub 2021 Jun 7.


Objectives: We investigated determinants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) anti-spike IgG responses in healthcare workers (HCWs) following one or two doses of Pfizer-BioNTech or Oxford-AstraZeneca vaccines.

Methods: HCWs participating in regular SARS-CoV-2 PCR and antibody testing were invited for serological testing prior to first and second vaccination, and 4 weeks post-vaccination if receiving a 12-week dosing interval. Quantitative post-vaccination anti-spike antibody responses were measured using the Abbott SARS-CoV-2 IgG II Quant assay (detection threshold: ≥50 AU/mL). We used multivariable logistic regression to identify predictors of seropositivity and generalized additive models to track antibody responses over time.

Results: 3570/3610 HCWs (98.9%) were seropositive >14 days post first vaccination and prior to second vaccination: 2706/2720 (99.5%) were seropositive after the Pfizer-BioNTech and 864/890 (97.1%) following the Oxford-AstraZeneca vaccines. Previously infected and younger HCWs were more likely to test seropositive post first vaccination, with no evidence of differences by sex or ethnicity. All 470 HCWs tested >14 days after the second vaccination were seropositive. Quantitative antibody responses were higher after previous infection: median (IQR) >21 days post first Pfizer-BioNTech 14 604 (7644-22 291) AU/mL versus 1028 (564-1985) AU/mL without prior infection (p < 0.001). Oxford-AstraZeneca vaccine recipients had lower readings post first dose than Pfizer-BioNTech recipients, with and without previous infection, 10 095 (5354-17 096) and 435 (203-962) AU/mL respectively (both p < 0.001 versus Pfizer-BioNTech). Antibody responses >21 days post second Pfizer vaccination in those not previously infected, 10 058 (6408-15 582) AU/mL, were similar to those after prior infection followed by one vaccine dose.

Conclusions: SARS-CoV-2 vaccination leads to detectable anti-spike antibodies in nearly all adult HCWs. Whether differences in response impact vaccine efficacy needs further study.

Keywords: Antibody; Quantitative anti-spike antibody; SARS-CoV-2; Serology; Vaccine.

MeSH terms

  • Adult
  • Antibodies, Viral / blood*
  • BNT162 Vaccine
  • COVID-19 / blood
  • COVID-19 Vaccines / immunology*
  • ChAdOx1 nCoV-19
  • Female
  • Health Personnel
  • Humans
  • Immunogenicity, Vaccine
  • Immunoglobulin G / blood
  • Male
  • Middle Aged
  • SARS-CoV-2 / immunology*
  • Spike Glycoprotein, Coronavirus / immunology*
  • Vaccination


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