Heterologous ChAdOx1-S/BNT162b2 Vaccination: Neutralizing Antibody Response to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Dear Editor,A recent report questioned whether one vaccine was better than another and how to evaluate this difference, but only homologous vaccination schedules were considered. Concern about the safety of the ChAdOx1-S vaccine have prompted some European countries to recommend using a heterologous booster, as proposed for mRNA vaccines for people under 55 years old . Immunogenicity and reactogenicity of a BNT162b2 booster in ChAdOx1-S-primed subjects was assessed in a multicenter, open-label, randomised, controled phase 2 trial, but included no homologous vaccination comparator. Few studies have compared the immune responses to homologous and heterologous vaccinationschedules in humans.