Antibody levels after BNT162b2 vaccine booster and SARS-CoV-2 Omicron infection

Highlights

• After booster vaccination antibody levels increase after 30 days with values much higher than first and second vaccination.

• After 60 and 90 days after booster dose, antibody levels decrease, suggesting the need of fourth dose.

• Compared with seronegative HCWs, a higher value was observed in HCWs infected by COVID-19 before vaccination, at all dosing times, because the values are the result of natural immunity along with induced by vaccination.

• 14.7% of HCWs contracted Omicron virus variant, however none of these showed severe symptoms.

Abstract

In the present study, immunogenicity data in 61 vaccinated healthcare workers (HCWs) either infection naïve (naïve HCWs) or with infection of Delta and/or Omicron COVID-19 (experienced HCWs) were evaluated up to 270 days after the second dose of BNT162b2 vaccine and up to 90 days after a booster dose. A decrease in antibody levels at 270 days following administration of the second dose (p = 0.0335) was observed, although values did not fall below the positivity threshold (33.8 BAU/ml). After booster vaccination, antibody levels increased after 30 days (p = 0.0486), with much higher values than after first and second vaccination. Antibody levels then decreased at 60 and 90 days after the booster dose. A comparison between mean antibody levels of naïve and experienced HCWs revealed higher values in experienced HCWs, resulting from both natural and vaccination-induced immunity. A total of 14.7% of HCWs contracted the Omicron virus variant after the vaccine booster, although none showed severe symptoms. These results support that a booster dose results in a marked increase in antibody response that subsequently decreases over time.