BNT162b2 Protection against the Omicron Variant in Children and Adolescents

To the Editor: Price and colleagues (published online on March 30 at NEJM.org)(1) describe the effectiveness of the BNT162b2 vaccine (Pfizer-BioNTech) against the B.1.1.529 (omicron) variant of SARS-CoV-2 in children and adolescents, findings that have important clinical relevance and policy implications. However, the study was designed without the inclusion of previous Covid-19 status as a confounding factor. It is well known that SARS-CoV-2 infection confers immune protection and appears to result in increased protection against severe Covid-19,(2) factors that could affect the evaluation of vaccine effectiveness. For instance, the vaccine effectiveness against hospitalization for Covid-19 did not appear to diminish . . .