1989年和1990年美国麻疹病例比前五年增加近6倍,大部分病例发生在未接种儿童特别是学龄前儿童中,但在接种疫苗儿童中病例也有所增加。在1岁以上接种儿童中,1989年和1990年麻疹病例平均为5872例,而1988年仅有1548例。最近发现麻疹疫苗病毒与当前流行病毒的基因有某些差异,从而人 The number of measles cases in the United States in 1989 and 1990 increased almost sixfold over the previous five years, with the majority of cases occurring in unvaccinated children, especially in preschool-age children, with an increase in the number of vaccinated children. Among children vaccinated over the age of 1 years, measles cases averaged 5872 in 1989 and 1990, compared with 1548 in 1988. Recently, there have been some differences between the measles vaccine virus and the genes of the current epidemic virus