SARS-CoV-2 vaccine breakthrough infections with the alpha variant are asymptomatic or mildly symptomatic among health care workers

Rovida, Francesca; Cassaniti, Irene; Paolucci, Stefania; Percivalle, Elena; Sarasini, Antonella; Piralla, Antonio; Giardina, Federica; Sammartino, Josè Camilla; Ferrari, Alessandro; Bergami, Federica; Muzzi, Alba; Novelli, Viola; Meloni, Alessandro; Cutti, Sara; Grugnetti, Anna Maria; Grugnetti, Giuseppina; Rona, Claudia; Daglio, Marinella; Marena, Carlo; Triarico, Antonio; Lilleri, Daniele; Baldanti, Fausto

Vaccine breakthrough SARS-CoV-2 infection has been monitored in 3720 healthcare workers receiving 2 doses of BNT162b2. SARS-CoV-2 infection is detected in 33 subjects, with a 100-day cumulative incidence of 0.93%. Vaccine protection against acquisition of SARS-CoV-2 infection is 83% (95%CI: 58-93%) in the overall population and 93% (95%CI: 69-99%) in SARS-CoV-2-experienced subjects, when compared with a non-vaccinated control group from the same Institution, in which SARS-CoV-2 infection occurs in 20/346 subjects (100-day cumulative incidence: 5.78%). The infection is symptomatic in 16 (48%) vaccinated subjects vs 17 (85%) controls (p = 0.01). All analyzed patients, in whom the amount of viral RNA was sufficient for genome sequencing, results infected by the alpha variant. Antibody and T-cell responses are not reduced in subjects with breakthrough infection. Evidence of virus transmission, determined by contact tracing, is observed in two (6.1%) cases. This real-world data support the protective effect of BNT162b2 vaccine. A triple antigenic exposure, such as two-dose vaccine schedule in experienced subjects, may confer a higher protection.