近20年来,已证实口服脊髓灰质炎活疫苗非常有效而且十分安全。对大多数易感幼儿坚持疫苗接种计划的国家,麻痹性脊髓灰质炎已几乎绝迹。早已认识到接种活疫苗后偶见麻痹病例发生。1969年世界卫生组织为了取得有关这种危险性的肯定资料和寻找减少危险性的方法,组织了一项协作研究。 For nearly 20 years, live oral polioviruses have proven to be very effective and very safe. Paralytic poliomyelitis has almost disappeared in countries that adhere to vaccination programs for the most vulnerable children. It has long been recognized that occasional paralysis occurs after vaccination. In 1969, WHO organized a collaborative study to obtain positive information on such risks and to find ways to reduce them.