A Comment article notes that in high-income countries with longstanding pertussis immunisation and high coverage, severe morbidity (especially death) from pertussis is concentrated in the narrow window before infants receive their first dose. In such countries, it suggests the UK experience provides good evidence of protection in this time-window, supporting the strong preference for pertussis vaccination in pregnancy over post-partum vaccination from modelling studies, and making an important contribution to national decision making.