COVID-19 vaccines are considered to have prevented an estimated tens of millions of SARS-CoV-2 infections and tens of thousands of COVID-19–related deaths in the US. However, the combination of reduced vaccine effectiveness against infection in the setting of Omicron sublineages and increased vaccination coverage has resulted in an increasing number of cases among vaccinated individuals. Designing and interpreting postauthorization, observational COVID-19 vaccine effectiveness studies have also become increasingly complex due to effects of prior infection on the risk and severity of repeat infections, emergence of variants that evade vaccine-induced immunity, waning immunity, more vaccine products and dosing schedules, and heterogeneity in outcomes measured within and across studies. The proper design and interpretation of vaccine effectiveness studies have consequences for vaccine research and policy decisions and for the public’s perception and trust of vaccines.
Source: JAMA Online First