Vicenti I, Basso M, Gatti F, et al. - Uninfected individuals completing the two-dose BNT162b2 mRNA COVID-19 vaccine schedule show a substantial neutralizing antibody titres (NtAb) decline at a significantly higher rate compared with previously infected, vaccinated individuals. A reasonable option to counteract this decline is administration of a third mRNA vaccine dose in these individuals. Among previously infected and not vaccinated individuals, two third had low but detectable Nabt levels after 13 months.

• Vaccinated HCW were assessed for NtAb prior to vaccination (V0), 20±2 days after the first dose (V1_20), 20±3 days (V2_20) and 90±2 days (V2_90) after the second dose and unvaccinated HCW were assessed after about 2 months (N_60), 10 months (N_300) and 13 months (N_390) from natural infection.

• Enrolled were 62 HCW.

• Infected HCW with no or mild disease had comparable NtAb at all the study points. Significantly lower NtAb was recorded in uninfected HCW relative to previously infected individuals.