傳染病動態模型來評估集團免疫 ─以小兒痲痺與手足口病為例

Abstract

疫苗不僅能對接種疫苗者產生直接保護的作用，也對未接種疫苗者產生間接保護的作用，這就是疫苗集團免疫（ herd immunity）的效應。過去很多文獻在探討疫苗的成本效益時，大多只考慮到疫苗的直接保護作用，大多忽略蜜月期、蜜月期後流行、流行期後新平衡與平均發病年齡改變等動態變化，以及這些動態變化與間接保護作用等對其成本效益所可能帶來的影響。 本研究建立了一個加入疾病症狀動態變化的傳染病模型，運用從過去小兒麻痺流行的文獻報告與由疾病管制局提供之手足口病的資料，來推估其R0值，並且比較傳統動態模型與新的症狀動態模型，並且藉此來量化集團免疫之效應。 結果新的症狀動態模型與傳統SIR模型，都能成功的估計小兒麻痺的R0值（1.71-24.17），而且結果相去不遠。可是新的症狀模型還能對臨床的併發症做預測，而且能輕易的評估疫苗與隔離等介入措施，對傳染病的影響。新的模型更能在資訊不完全下，因為加入了動態的臨床症狀之觀點，成功的推估手足口病的R0值（1.07-1.67）。而上述這些狀況都不是傳統的傳染病模型可以做到的。 總結，本研究所提出之新的症狀模型，保有傳統動態模型的所有優點，還能對臨床的併發症做預測，更能輕易的評估介入措施對傳染病的影響，並能量化集團免疫的效應。此模型對於經濟效益評估上，比傳統模型更具優勢。所以建議未來建立傳染病模型時，應將症狀的動態變化，放入評估的模型中。

Mass vaccination can protect not only the immunized individual against infection disease but also protect the un-immunized individual. The effect of indirect protection of susceptible is termed herd immunity or herd effect. Herd immunity and herd immunity affect not only the incidence of disease but also the economic analysis of vaccination program. But the effect of herd effect in the study of economic analysis about vaccine program almost was ignored in the past. Our modified dynamic symptom model was based on not only the dynamic infectious status but also dynamic change of disease with complications. We demonstrated it with illustrations of polio and hand-foot-mouth disease (HFMD). The effective reproductive number (R) of polio was estimated around 1.71-24.17. The effective R of HFMD was estimated around 1.07-1.67. If there are many uncertainties in emerging diseases like the HFMD with severe symptoms, the simple SIR model isn’t easily applied to this condition. But our modified dynamic symptoms model can easily handle this condition. The modified model is more easily applied to the dynamic economic analysis of the intervention program.