de Azeredo Costa E, Morris L
Am J Epidemiol. 1975 Jun;101(6):552-61. doi: 10.1093/oxfordjournals.aje.a112126.
The most severe outbreak of smallpox in Brazil in 1969 took place in the municipio of Utinga, Bahia. Of 507 cases, 246 occurred in residents of the urban area of the municipio. This paper describes the findings of the detailed study of the urban area outbreak. An inverse relationship between age and susceptibility was evident; fully 91% of the children less than 5 years of age as well as 75% of the school-age children had no history of smallpox and had never been vaccinated. The overall attack rate was 11% with nearly three-fourths of the cases in children under 15 years of age. Only 4 of the 246 patients had a vaccination scar, and the estimate of vaccine efficacy was 94%. The continued occurrence of cases after the initial vaccination containment measures prompted detailed studies during 2 follow-up visits to the community which demonstrated that 1) transmission of smallpox may continue in a pocket of susceptibles although the overall immune status of a community is high following containment measures, and 2) clinical illness may have been aborted in those affected individuals who were only in their second to fourth day of incubation at the time of vaccination.
1969年巴西最严重的天花疫情发生在巴伊亚州的乌廷加市。在507例病例中，有246例发生在该市市区居民中。本文描述了对市区疫情详细研究的结果。年龄与易感性之间存在明显的反比关系；5岁以下儿童中足足91%以及学龄儿童中75%均无天花病史且从未接种过疫苗。总体发病率为11%，近四分之三的病例发生在15岁以下儿童中。246例患者中只有4人有接种疤痕，疫苗效力估计为94%。在最初的疫苗接种控制措施实施后仍有病例持续出现，这促使在对该社区进行的2次随访期间开展了详细研究，研究表明：1）尽管在控制措施实施后社区的总体免疫状况较高，但天花仍可能在一群易感人群中继续传播；2）对于那些在接种疫苗时仅处于潜伏期第二至第四天的受感染个体，临床疾病可能已被阻断。
