英国设德兰某地有居民721人,其中144人是16岁以下的儿童。该地于1974年7月停止百日咳预防接种,在此前出生的99名儿童中,93名(94%)曾经接种过该菌苗,此后出生的35名儿童全未接种。当地在最近15年中不曾有过百日咳流行。1977年10月2日第一名患者(15岁,女)出现百日咳症状。她的妹妹(8岁)在10天以后也患了百日咳。到10 There are 721 inhabitants of Shetland, England, 144 of whom are children under the age of 16. In July 1974, the district stopped the vaccination against whooping cough. Of the 99 children born previously, 93 (94%) had been vaccinated against the disease and none of the 35 children born thereafter were vaccinated. The locality has not had the pertussis epidemic in the last 15 years. The first patient (15 years old, female) on October 2, 1977 developed pertussis symptoms. Her sister (8 years old) also had pertussis 10 days later. To 10