Bergwerk M, Gonen T, Lustig Y, et al. - The BNT162b2 messenger RNA vaccine has been identified to have high efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The rare breakthrough infections, including infections among health care workers, led researchers to seek data characterizing these infections and define correlates of breakthrough and infectivity. At the largest medical center in Israel, they assessed 1,497 fully vaccinated health care workers for whom RT-PCR data were available. Among these, 39 SARS-CoV-2 breakthrough infections were documented. Lower neutralizing antibody titers during the peri-infection period were observed to be linked with the occurrence of breakthrough infections with SARS-CoV-2. Despite being mild or asymptomatic, most breakthrough infections presented with persistent symptoms.