Moulton L H, Chung S, Croll J, Reid R, Weatherholtz R C, Santosham M
Center for American Indian and Alaskan Native Health, Department of International Health, Baltimore, MD 21205, USA.
Int J Epidemiol. 2000 Aug;29(4):753-6. doi: 10.1093/ije/29.4.753.
Oropharyngeal carriage studies of Haemophilus influenzae type b (Hib) and the rapid drop in Hib invasive disease in countries with widespread Hib conjugate vaccine immunization programmes for infants have indicated there may be significant indirect effects (herd immunity) associated with these vaccines. Our goal was to quantify the magnitude of these effects in an American Indian population during its early years of Hib immunization.
In a synthetic case-cohort study, we combined data from an efficacy trial, an immunization uptake records survey, and ongoing surveillance for Hib disease on the Navajo Nation from 1988 to 1992. Decline in the incidence of invasive Hib disease among children <2 years old was estimated via proportional hazards survival models as a function of individual immunization status and the proportion of immunized children in a community.
The predominant vaccine during the study period was Hib-OMPC (92% of immunizations). The effectiveness of receipt of at least one dose was 97.2%. Compared to communities with 0-20% coverage with at least one dose, residence in communities with 20-40% and 40-60% coverage was associated with risk reductions of 56.5% and 73.2%, respectively.
The results indicate substantial indirect effects of Hib-OMPC immunization may occur even at relatively low levels of immunization coverage. Countries that implement Hib immunization programmes may receive greater benefits at the community level than those due to the direct protection conferred to the individual through vaccination.
对b型流感嗜血杆菌（Hib）的口咽部携带情况研究以及在为婴儿广泛开展Hib结合疫苗免疫计划的国家中Hib侵袭性疾病的迅速下降表明，这些疫苗可能存在显著的间接效应（群体免疫）。我们的目标是在一个美国印第安人群体进行Hib免疫的早期阶段量化这些效应的大小。
在一项综合病例队列研究中，我们合并了1988年至1992年在纳瓦霍族进行的一项疗效试验、一项免疫接种率记录调查以及对Hib疾病的持续监测的数据。通过比例风险生存模型，根据个体免疫状况和社区中免疫儿童的比例，估计2岁以下儿童侵袭性Hib疾病发病率的下降情况。
研究期间主要使用的疫苗是Hib-OMPC（92%的免疫接种）。接种至少一剂疫苗的有效性为97.2%。与至少一剂疫苗覆盖率为0-20%的社区相比，居住在覆盖率为20-40%和40-60%的社区，风险分别降低了56.5%和73.2%。
结果表明，即使在免疫覆盖率相对较低的情况下，Hib-OMPC免疫接种也可能产生显著的间接效应。实施Hib免疫计划的国家在社区层面可能获得比通过疫苗接种直接给予个体的保护更大的益处。
