Antibody response induced by the BNT162b2 mRNA COVID-19 vaccine in a cohort of health-care workers, with or without prior SARS-CoV-2 infection: a prospective study

Dora Buonfrate, Chiara Piubelli, Federico Gobbi, Davide Martini, Giulia Bertoli, Tamara Ursini, Lucia Moro, Niccolò Ronzoni, Andrea Angheben, Paola Rodari, Chiara Cardellino, Francesca Tamarozzi, Stefano Tais, Eleonora Rizzi, Monica Degani, Michela Deiana, Marco Prato, Ronaldo Silva, Zeno Bisoffi

Research output: Contribution to journalArticlepeer-review


OBJECTIVES: To assess the antibody response to BNT162b2 mRNA COVID-19 vaccine in a cohort of health-care workers (HCW), comparing individuals with previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and SARS-CoV-2-naive individuals.

METHODS: HCW were tested at T0 (day of first dose), T1 (day of second dose) and T2 (2-3 weeks after second dose) for IgG anti-nucleocapsid protein, IgM anti-spike protein and IgG anti-receptor binding domain (IgG-RBD-S). The antibody response was compared between four main groups: group A, individuals with previous infection and positive antibodies at baseline; group B, individuals with the same history but negative antibodies; group C, individuals with no infection history but positive antibodies; group D, naive individuals. Repeated measures analysis was used to compare results over time-points.

RESULTS: A total of 1935 HCW were included. Median IgG-RBD-S titre was significantly higher for group A (232 individuals) than for group B (56 individuals) both at T1 (A: 22 763 AU/mL, interquartile range (IQR) 14 222-37 204 AU/mL; B: 1373 AU/mL, IQR 783-3078 AU/mL, p 0.0003) and T2 (A: 30 765 AU/mL, IQR 19 841-42 813 AU/mL; B: 13 171 AU/mL, IQR 2324-22 688 AU/mL, p 0.0038) and for group D (1563 individuals; 796 AU/mL, IQR 379-1510 AU/mL at T1; 15 494 AU/mL, IQR 9122-23 916 AU/mL at T2, p < 0.0001 for both time-points). T1 values of group A were also significantly higher than T2 values of group D (p < 0.0001). Presence of symptoms, younger age and being female were associated with stronger antibody response. HCW infected in March showed a significantly stronger response (T1: 35 324 AU/mL, IQR 22 003-44 531 AU/mL; T2: 37 648 AU/mL, IQR 27 088-50 451 AU/mL) than those infected in November (T1: 18 499 AU/mL, IQR 11 492-27 283 AU/mL; T2: 23 210 AU/mL, IQR 18 074-36 086 AU/mL, p < 0.0001 for both time-points.

CONCLUSIONS: Individuals with past SARS-CoV-2 infection had a strong antibody response after one single vaccine shot. A single dose might be sufficient for this group, regardless of the time elapsed since infection; however, the clinical correlation with antibody response needs to be studied.

Original languageEnglish
Pages (from-to)1845-1850
Number of pages6
JournalClinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases
Issue number12
Publication statusPublished - Dec 2021


  • Antibodies, Viral/blood
  • Antibody Formation
  • BNT162 Vaccine/immunology
  • COVID-19/prevention & control
  • Health Personnel
  • Humans
  • Immunoglobulin G/blood
  • Prospective Studies
  • RNA, Messenger


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