Clinical Characteristics of Healthcare Workers with SARS-CoV-2 Infection after Vaccination with BNT162b2 Vaccine

Abstract Background: The pandemic of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has hardly affected the entire world. Vaccines against COVID-19 appear as a tool able to curb out the mortality and to reduce the circulation of the virus. Little is known so far about the clinical characteristics of individuals who developed SARS-CoV-2 infection after having received the vaccination, as well as the temporal relationship between vaccine administration and symptoms onset.Methods: Retrospective cohort study among the healthcare workers (HCWs) of the Fondazione IRCCS Ospedale Maggiore Policlinico of Milano, vaccinated with the BNT162b2 vaccine who developed SARS-CoV-2 infection (documented through positive RT-PCR on NPSs). Results: Overall, we have identified 15 HCWs with SARS-CoV-2 infection after vaccination, 7 (46.7%) of them were male and the mean age was 38.4 years (SD 14). In 4 of them the presence of SARS-CoV-2 anti-nucleocapside (anti-N) antibodies was assessed before vaccination and resulted positive in 1 case. In all HCWs the presence of SARS-CoV-2 anti-spike (anti-S1) antibodies was assessed, in average 42.2 days after the completion of vaccination, with a mean value of 2,055 U/mL (SD 1,927.3). SARS-CoV-2 infection was ascertained in average 56.2 days after vaccination. The mean cycle threshold (Ct) of SARS-CoV-2 PCR was 26.4, the lineage was characterized in 9 HCWs. None of the HCWs reported a primary or secondary immunodeficiency. Regarding symptoms, they were reported only by 7 (46.7%) HCWs and appeared on average 55 days after the second dose of vaccination. Of those who reported symptoms, one (14.3%) had fever, 7 (100%) rhinitis/conjunctivitis, 4 (57.1%) taste and smell alterations, none had respiratory symptoms, 4 headache/arthralgia (57.1%) and 1 gastrointestinal symptoms (14.3%). All symptoms disappeared in a few days and no other unclassified symptoms were reported.Conclusions: Infections occurring after vaccination with BNT162b2 vaccine are mostly asymptomatic and are not associated with the serum titre of anti-S1 antibodies. We did not find a predominance of a specific viral variants, with several lineages represented.