Evidence of whooping-cough-vaccine efficacy from the 1978 whooping-cough epidemic in Hertfordshire.

The question of the efficacy of whooping-cough immunisation was central to the controversy that started in 1974. Definitive answers were not possible at the time because of the very low levels of whooping-cough in the preceding years and the absence of up-to-date information. The widespread abandonment of whooping-cough immunisation and the subsequent epidemic of whooping-cough have provided a natural epidemiological experiment. Figures from Hertfordshire in 1978 show that for children aged 4 years and under whooping-cough immunisation conferred 92% protection.