Reply to Fung et al. on COVID‐19 vaccine case‐counting window biases overstating vaccine effectiveness.

EXPERIMENTAL design; COVID-19; CLINICAL trials; IMMUNIZATION; COVID-19 vaccines; TIME; VACCINE effectiveness; RISK assessment; PATIENT monitoring; TREATMENT effectiveness; MESSENGER RNA; RESEARCH bias; VACCINATION status; PATIENT safety

The article focuses on critiquing and expanding upon the concept of case-counting window bias in observational studies of mRNA COVID-19 vaccine effectiveness. It highlights the potential for this bias to be more pronounced than initially suggested, particularly due to definitional biases, and discusses its implications for both perceived effectiveness and safety monitoring.