Monath T P, Nasidi A
OraVax Inc., Cambridge, Massachusetts.
Am J Trop Med Hyg. 1993 Feb;48(2):274-99. doi: 10.4269/ajtmh.1993.48.274.
The cost-effectiveness of preventive yellow fever vaccination versus emergency mass vaccination campaigns for epidemic control remains a matter of controversy. Until recently, Nigeria and other anglophone countries in West Africa most severely afflicted by yellow fever epidemics have followed a policy of emergency control. The effects of including yellow fever 17D vaccine in the Expanded Program of Immunization (EPI) on the immune status of the Nigerian population was studied under conservative assumptions of vaccine coverage and efficacy. The model defined the age-specific prevalence of immunity resulting from vaccination of infants and from natural endemic infection beginning in 1991 and extending over a time horizon of 35 years. The data were used to predict the number of cases and deaths during hypothetical epidemics in 2006 and 2026, representing the historic periodicity of epidemics. A second model was used to demonstrate that a > or = 60% prevalence of immunity would preclude epidemic yellow fever transmission; under base case assumptions, this prevalence would be reached after 18 years of initiating routine yellow fever vaccination in the Guinea savannah zone, the region most often affected by epidemics. Using assumptions based on data from other African countries, the cost of adding yellow fever vaccine to the existing EPI was estimated as +0.65 per fully immunized child, whereas the cost of emergency vaccination in the face of an epidemic was estimated as +7.84/person. Vaccine coverage rates achievable by the EPI were modeled on recent successes with measles vaccine, and began in 1991 at 60%. The effective vaccine coverage rate in an emergency campaign was taken as 10%, based on recent experience. For an epidemic of moderate size in 2006 (morbidity similar to the documented outbreak in 1987), the cost-effectiveness of emergency mass immunization for control of hypothetical yellow fever epidemics was two-fold higher ($381/case and $1,904/death prevented) than that of the EPI ($763/case and $3,817/death prevented). However, despite its higher cost, the efficiency of the EPI was seven-fold greater in terms of cases and deaths prevented. In large epidemics, such as that occurring over successive years (1986-1991) in Nigeria, cost-effectiveness of the EPI exceeded that of emergency control. The EPI may also play an important role in the prevention of endemic yellow fever. Assuming annual rates of endemic yellow fever predicted by serologic surveys, routine vaccination would significantly reduce morbidity and mortality at cost-effectiveness ratios within the range for other diseases prevented by the EPI, including polio, tetanus, and diphtheria.(ABSTRACT TRUNCATED AT 400 WORDS)
预防性黄热病疫苗接种与用于疫情控制的应急大规模疫苗接种运动的成本效益仍然存在争议。直到最近，受黄热病疫情影响最严重的尼日利亚和西非其他英语国家一直遵循应急控制政策。在疫苗覆盖率和效力的保守假设下，研究了将黄热病17D疫苗纳入扩大免疫规划（EPI）对尼日利亚人群免疫状况的影响。该模型确定了从1991年开始并在35年时间范围内，婴儿接种疫苗和自然地方性感染所产生的特定年龄免疫流行率。这些数据用于预测2006年和2026年假设疫情期间的病例数和死亡数，这代表了疫情的历史周期。第二个模型用于证明免疫流行率≥60%将阻止黄热病疫情传播；在基本情况假设下，在几内亚草原地区（最常受疫情影响的地区）开始常规黄热病疫苗接种18年后将达到这一流行率。根据其他非洲国家的数据进行假设，将黄热病疫苗添加到现有EPI中的成本估计为每名完全免疫儿童增加0.65美元，而面对疫情时应急接种的成本估计为每人7.84美元。EPI可实现的疫苗覆盖率根据麻疹疫苗近期的成功情况进行建模，1991年开始时为60%。根据近期经验，应急接种运动中的有效疫苗覆盖率为10%。对于2006年中等规模的疫情（发病率与1987年记录的疫情相似），用于控制假设黄热病疫情的应急大规模免疫的成本效益（预防每例病例381美元和每例死亡1904美元）是EPI的两倍（预防每例病例763美元和每例死亡3817美元）。然而，尽管成本较高，但EPI在预防病例和死亡方面的效率高出七倍。在大规模疫情中，例如尼日利亚在连续几年（1986 - 1991年）发生的疫情，EPI的成本效益超过了应急控制。EPI在预防地方性黄热病方面也可能发挥重要作用。假设血清学调查预测的地方性黄热病年发病率，常规疫苗接种将以与EPI预防的其他疾病（包括脊髓灰质炎、破伤风和白喉）范围内的成本效益比显著降低发病率和死亡率。（摘要截短至400字）
