Williams B G, Cutts F T, Dye C
Epidemiology Research Unit, Johannesburg, South Africa.
Epidemiol Infect. 1995 Dec;115(3):603-21. doi: 10.1017/s0950268800058763.
Where immunization campaigns locally eliminate measles, it will be important to identify the vaccination policy most likely to prevent future epidemics. The optimum age for vaccination depends on the rate of decline of maternal antibody, because the presence of antibody reduces vaccine efficacy. The first part of this paper contains a quantitative reappraisal of the data on antibody decline and seroconversion rates by age. The decline in maternal antibody protection follows delayed exponentials, with delays of 2-4 months, and subsequent half-lives of 1-2 months. Using this result in an analytical mathematical model we find that the optimal age to administer a single dose of vaccine to children, which is independent of vaccine coverage, lies within the range 11-19 months. We also show that, where the optimal age cannot be met, it is better to err towards late rather than early vaccination. There are therefore two reasons why developing countries, which presently vaccinate during infancy because measles transmission rates are high should eventually switch to the second year of life. The possible gains from two-dose vaccination schedules are explored with respect to both coverage and efficacy. A two-dose schedule will be beneficial, in principle, only when there is a need to increase net vaccine efficacy, after coverage has been maximized with a one-dose schedule.
在通过当地免疫接种活动消除麻疹的地区，确定最有可能预防未来疫情的疫苗接种政策非常重要。最佳接种年龄取决于母体抗体的下降速度，因为抗体的存在会降低疫苗效力。本文第一部分对不同年龄的抗体下降和血清转化率数据进行了定量重新评估。母体抗体保护的下降呈延迟指数形式，延迟2 - 4个月，随后半衰期为1 - 2个月。在一个分析数学模型中运用这一结果，我们发现给儿童接种单剂疫苗的最佳年龄在11 - 19个月范围内，且与疫苗接种覆盖率无关。我们还表明，如果无法达到最佳年龄，宁可接种延迟也不要提前。因此，目前由于麻疹传播率高而在婴儿期进行接种的发展中国家最终应转向在儿童第二年接种，有两个原因。针对覆盖率和效力探讨了两剂疫苗接种方案可能带来的益处。原则上，只有在用单剂接种方案使覆盖率最大化之后，需要提高疫苗净效力时，两剂接种方案才会有益。
