Abstract

SARS-CoV-2 vaccines are highly efficient against severe forms of the disease, hospi-talization and death. Nevertheless, insufficient protection against several circulating viral variants might suggest waning immunity and the need for an additional vaccine dose. We conducted a longitudinal study on the kinetics and persistence of immune responses in healthcare workers vaccinated with two doses of BNT162b2 mRNA vac-cine with or without prior SARS-CoV-2 infection. No new infections were diagnosed during follow-up. At 6 months, post-vaccination or post-infection, despite a down-ward trend in the level of anti-S IgG antibodies, the neutralizing activity does not decrease significantly, remaining higher than 75% (85.14% for subjects with natural infection, 88.82% for vaccinated after prior infection and 78.37% for vaccinated only). In a live-virus neutralization assay, the highest neutralization titres were present at baseline and at 6 months follow-up in persons vaccinated after prior infection. Anti-S IgA levels showed a significant descending trend in vaccinated subjects (p<0.05) after 14 weeks. Cellular immune responses are present even in vaccinated partici-pants with declining antibody levels (index ratio 1.1–3) or low neutralizing activity (30%–40%) at 6 months, although with lower T-cell stimulation index (p=0.046) and IFN- γ secretion (p= 0.0007) compared to those with preserved humoral responses.

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