The effect of vaccination coverage and climate on Japanese encephalitis in Sarawak, Malaysia.
The effect of vaccination coverage and climate on Japanese encephalitis in Sarawak, Malaysia.
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DOI：
10.1371/journal.pntd.0002334
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发表时间：
2013
影响因子：
3.8
通讯作者：
Solomon T
中科院分区：
文献类型：
--
作者：
Impoinvil DE;Ooi MH;Diggle PJ;Caminade C;Cardosa MJ;Morse AP;Baylis M;Solomon T
日本脑炎（JE）是亚洲病毒性脑炎的主要原因，每年约有70，000例病例，10，000至15，000例死亡。由于乙脑发病率随时间变化很大，部分原因是年际气候变化对蚊媒丰度的影响，因此评估疫苗接种计划的效果变得更加复杂，因为气候或多或少有利的年份也可能导致疫苗接种后发病率的变化。因此，本研究的目的是量化疫苗接种对马来西亚沙捞越确诊的日本脑炎（JE）病例的影响，控制气候变化后，以更好地了解JE病毒传播和控制的时间动态。从1997年至2006年，从沙捞越诗巫医院获得了经血清学证实的乙脑病例的每月数据。乙脑疫苗接种率（非疫苗接种年份与疫苗接种年份）和气象预测变量，包括温度，降雨量和南方涛动指数（SOI）进行了测试，其与乙脑病例使用泊松时间序列分析和控制的季节性和长期趋势。在10年的监测期间，确定了133例日本脑炎确诊病例。在不考虑气候影响的情况下，接种疫苗后，估计乙脑风险降低了61%。当在模式中控制了气候年际变率的影响时，这种减少仅约为45%。Poisson模型分析表明，降水量（滞后1个月）、最低气温（滞后6个月）和SOI（滞后6个月）与乙脑病例呈正相关。这项研究通过考虑气候年际变化，首次改进了对接种疫苗减少乙脑的估计。我们的分析证实，接种疫苗大大降低了砂拉越的乙脑风险，但如果忽略气候影响，这种好处可能会被高估。日本脑炎（JE）病毒是一种蚊媒病毒，是亚洲病毒性脑炎的主要原因。人类乙脑病例的累积发病率似乎很低（2例/105/年）;然而，流行病是集中和严重的，集中在1至15岁的儿童中，在空间上高度聚集。尽管有针对乙脑病毒（JEV）的疫苗，但亚洲仍有大量乙脑病例。在印度尼西亚和孟加拉国等一些国家，由于水稻种植和养猪业的增加以及这些地区缺乏疫苗接种或病媒控制计划，疾病病例可能会增加。然而，鉴于JEV传播对气候的敏感性，通过对蚊子媒介的影响，气候的变化可能会增加或减少JEV的传播。显然，接种乙脑疫苗大大减少了乙脑病例，但尚不清楚气候是否对我们估计疫苗效果的能力有任何混杂影响。我们发现，自接种疫苗以来，日本脑炎病例减少的大约四分之一可能是由于气候对该病不利的年份，而不是疫苗接种的效果。考虑到气候影响，涉及气候敏感性疾病的疫苗接种研究可能会更加准确。
Japanese encephalitis (JE) is the leading cause of viral encephalitis across Asia with approximately 70,000 cases a year and 10,000 to 15,000 deaths. Because JE incidence varies widely over time, partly due to inter-annual climate variability effects on mosquito vector abundance, it becomes more complex to assess the effects of a vaccination programme since more or less climatically favourable years could also contribute to a change in incidence post-vaccination. Therefore, the objective of this study was to quantify vaccination effect on confirmed Japanese encephalitis (JE) cases in Sarawak, Malaysia after controlling for climate variability to better understand temporal dynamics of JE virus transmission and control. Monthly data on serologically confirmed JE cases were acquired from Sibu Hospital in Sarawak from 1997 to 2006. JE vaccine coverage (non-vaccine years vs. vaccine years) and meteorological predictor variables, including temperature, rainfall and the Southern Oscillation index (SOI) were tested for their association with JE cases using Poisson time series analysis and controlling for seasonality and long-term trend. Over the 10-years surveillance period, 133 confirmed JE cases were identified. There was an estimated 61% reduction in JE risk after the introduction of vaccination, when no account is taken of the effects of climate. This reduction is only approximately 45% when the effects of inter-annual variability in climate are controlled for in the model. The Poisson model indicated that rainfall (lag 1-month), minimum temperature (lag 6-months) and SOI (lag 6-months) were positively associated with JE cases. This study provides the first improved estimate of JE reduction through vaccination by taking account of climate inter-annual variability. Our analysis confirms that vaccination has substantially reduced JE risk in Sarawak but this benefit may be overestimated if climate effects are ignored. Japanese encephalitis (JE) virus is a mosquito-borne virus which is the leading cause of viral encephalitis in Asia. The cumulative attack rate for human JE cases is seemingly low (2-cases/105/year); however, epidemics are focal and intense, being concentrated in children 1 to 15 years of age and highly clustered spatially. Despite the availability of a vaccine against JE virus (JEV), a significant number of JE cases still occur in Asia. Increases in disease cases may occur in some countries, such as Indonesia and Bangladesh, due to increasing rice cultivation, pig husbandry and lack of vaccination or vector control programs in these areas. However, given the sensitivity of JEV transmission to climate through impacts on the mosquito vectors, changes in climate may increase or decrease JEV transmission. Clearly, JE vaccination has substantially reduced JE cases, but it is not clear if climate has any confounding impact on our ability to estimate vaccine effect. We found that approximately one quarter of the reduction in JE cases since vaccination was introduced might be attributable to climatically unfavourable years for the disease, rather than the effect of vaccination. Vaccination studies involving climate-sensitive diseases may be made more accurate by taking climate effects into account.
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