PROS1 and severe acute respiratory syndrome: Two doses of BNT162b2 induced Ab against the S protein of other betacoronaviruses, with novel induction of IgG against severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) viruses (Figure S3C) and boosting of baseline IgG against the human seasonal betacoronaviruses HKU1 and OC43.