Background

No large-scale Zika epidemic has been observed to date in Southeast Asia following the 2015-16 Latin American and the Caribbean epidemic. One hypothesis is Southeast Asian populations’ partial immunity to Zika.

Method

We estimated the two conditions for a Zika outbreak emergence in Southeast Asia: (i) the risk of Zika introduction from Latin America and the Caribbean and, (ii) the risk of autochthonous transmission under varying assumptions on population immunity. We also validated the model used to estimate the risk of introduction by comparing the estimated number of Zika seeds introduced into the United States with case counts reported by the Centers for Disease Control and Prevention (CDC).

Results

There was good agreement between our estimates and case counts reported by the CDC. We thus applied the model to Southeast Asia and estimated that, on average, 1–10 seeds were introduced into Indonesia, Malaysia, the Philippines, Singapore, Thailand and Vietnam. We also found increasing population immunity levels from 0 to 90% reduced probability of autochthonous transmission by 40% and increasing individual variation in transmission further reduced the outbreak probability.

Conclusions

Population immunity, combined with heterogeneity in transmission, can explain why no large-scale outbreak was observed in Southeast Asia during the 2015-16 epidemic.

中文翻译：

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定量研究在2015-16年拉丁美洲和加勒比海地区流行期间寨卡病毒在亚洲传播的风险。

背景

在2015-16年拉丁美洲和加勒比地区流行之后，东南亚至今尚未发现大规模的寨卡流行病。一种假设是东南亚人口对寨卡病毒的部分免疫力。

方法

我们估计了在东南亚出现寨卡病毒爆发的两个条件：（i）从拉丁美洲和加勒比地区引进寨卡病毒的风险，以及（ii）在对人口免疫力的各种假设下发生自发传播的风险。我们还通过将估计的引入美国的Zika种子数量与疾病控制与预防中心（CDC）报告的病例数进行比较，验证了用于估算引入风险的模型。

结果

我们的估计数与疾病预防控制中心报告的病例数之间有很好的一致性。因此，我们将模型应用于东南亚，并估计平均有1-10种种子被引入印度尼西亚，马来西亚，菲律宾，新加坡，泰国和越南。我们还发现，将群体免疫水平从0％提高到90％，会使自体传播的可能性降低了40％，而传播中个体差异的增加进一步降低了爆发可能性。

结论

人口免疫力与传播的异质性相结合，可以解释为什么在2015-16流行期间东南亚未观察到大规模爆发。