Neutralizing antibody responses in healthcare personnel after three doses of mRNA BNT162b2 vaccine and association with baseline characteristics and past SARS-CoV-2 infection.

Aim: To estimate neutralizing antibody (NAb) immunity against SARS-CoV-2 in 739 healthcare personnel (HCP) vaccinated with three doses of BNT162b2 mRNA vaccine.

Methods: Serum samples were collected at 3, 6, and 9 months after the second vaccine dose and at 7-55 days after the third dose. Samples were tested for NAbs against SARS-CoV-2 receptor binding domain.

Results: The mean inhibition rates at 3, 6, and 9 months after the second dose were 86.33%, 73.38%, and 61.18%, and increased to 95.57% after the booster dose. Younger HCP and HCP with past SARS-CoV-2 infection had higher inhibition rates while there was an inverse correlation between NAb levels and comorbidities or tobacco use (p-values < 0.001). Increased NAb titers were also noticed in women (p-value = 0.033), especially at the end of the 9-month study period.

Conclusion: NAb levels increased considerably after a booster mRNA vaccine dose. Host factors and past SARS-CoV-2 infection influence NAb titers.