以機率模式進行水痘疫苗之經濟評估: 考慮水痘及帶狀疱疹之影響

Abstract

雖然水痘疫苗的成效已知，但由於有(1)延後水痘病毒感染的年齡可能增加罹患水痘的疾病嚴重度及(2)缺乏環境中激發免疫力機會而使免疫力下降而導致帶狀疱疹發病這兩項爭議，目前全面施打水痘疫苗的長期效益仍無定見。過去只有少數文獻曾考慮許多與水痘病毒感染疾病相關參數的不確定性，且從不同層面評估水痘疫苗的全面性施打。 研究目的 建構水痘病毒感染的傳染模式，並藉此對未來針對十二個月大嬰兒全面施打水痘病毒疫苗的政策，從醫療提供者、消費者、與社會等多種角度，且考慮該疫苗對台灣帶狀泡疹疾病發生的長期影響，進行經濟性評估。 方法 建構馬可夫鏈模式以模擬水痘與帶狀泡疹及兩疾病之併發症在未施打疫苗前的自然病史，利用文獻中關於水痘疫苗成效的參數、全面調查民眾付費意願的資料，與直接與間接成本估算，自不同觀點比較全面施打水痘疫苗與不施打水痘疫苗的成本效果、成本效用及成本效益。我們使用固定機率與機率分布兩種方法預估增加成本效果比、增加成本效用比、增加成本效益比及淨效益等。 結果 模擬結果顯示，施打疫苗之後不但可減少76%的水痘感染與72%的帶狀泡疹發生率，還可以減少兩疾病71%至90%的併發症與死亡率。使用固定機率模式與機率分布模式，分別從醫療提供者觀點與社會的觀點角度出發，所有的增加成本皆為負值，施打疫苗比較不施打疫苗，既得到更多效益又節省成本。以固定機率模式，從醫療提供者觀點，我們預估每支出NTD 1元的疫苗成本，可回收NTD 1.17元的效益；從社會角度來看，每支出一元疫苗成本，可回收NTD 1.76元的效益，顯示不論從醫療提供者與社會觀點而言，疫苗施打政策都具有成本效益。 依據付費意願調查資料以消費者觀點而言，成本與效益的差額達NTD 185,600,000元的預估付費意願。從社會觀點來看，效益還更高。應用機率分布模式，我們估測其平均值為NTD 185,600,000元(95% CI: NTD 170,000,000 – NTD 200,000,000)。 結論 透過對短期與長期結果進行正式的經濟評估，結果發現對醫療提供者觀點、社會觀點或是消費者觀點而言，全面施打疫苗不但具成本效果，還符合成本效益，因此全面水痘疫苗施打的政策值得支持。

Abstract Introduction Although the efficacy of varicella vaccination has been demonstrated, it is still unclear whether there is a long-term benefit after universal vaccination, which has been argued with lacking of boosting leading to weak immunity and the severe disease due to the delay age. The failure of reaching consensus may be also involved in costs implicated from different viewpoints. Very few studies on economic evaluation have been conducted to address these issues based on different perspective and taken the joint uncertainty of parameters. Objectives We aimed at constructing the transmission model of varicella zoster virus infection to perform an economic evaluation for varicella vaccination at age of 12 month old, considering the long-term impact on herpes zoster in Taiwan, from health care payer’s perspective, consumer’s and the societal perspective. Methods An analytic-decision Markov model was developed to model the disease natural history of varicella and herpes zoster infection together with the sequalae of two infections in the absence of vaccination. By the application of the vaccine efficacy from literature review, willingness to pay from empirical survey, and the incorporation of direct and indirect cost, a decision on universal vaccination, was compared with no vaccination by three types of formal economic evaluation, cost-effectiveness analysis, cost-utility analysis, and cost-benefit analysis, given different perspectives. Both deterministic and probabilistic approaches were used to estimate incremental cost-effectiveness ratios, incremental cost-utility ratio, benefit-cost ratio, and net benefit. Results The simulated results found the uptake of vaccination program may not only lead to 76% and 72% reduction of varicella cases and herpes zoster, respectively, but also averted 71%-90% complications or deaths pertaining to varicella and herpes zoster. By using deterministic approach, the incremental cost ratio in cost-effectiveness analysis, vaccination was dominant over no vaccination from both healthcare payer’s and societal perspectives. From both perspectives, dominant results were obtained using probabilistic approach. Negative estimates from both healthcare payer’s and societal perspectives indicated the dominance of vaccination over no vaccination. In cost-benefit analysis, using a deterministic approach, a NTD 1.17 of benefit/cost ratio was estimated, suggesting a 0.17 more dollars returned benefit per dollar invested in vaccination if we take healthcare payer’s perspective. Given societal perspective, the benefit/cost ratio was increased to NTD 1.76, amounting to have NTD 1 invested in vaccination in return for approximately NTD 2. The results of estimating the absolute net benefit based on willingness to pay showed given health care perspective, there was a total of NTD 185,600,000 net balance between net cost and net benefit from health perspective. A larger benefit was seen from societal perspective. By the application of a probabilistic approach, we produced the mean value of NTD 185,600,000 (95% CI: NTD 170,000,000- NTD 200,000,000) with a range between NTD 170,000,000 and NTD 200,000,000. A large benefit was also seen when societal perspective was taken. Conclusion Using a formal economic evaluation making allowance for both short-term and long-term outcome, we concluded Universal vaccination seem both cost-effective and cost-beneficial if healthcare payer, societal, and consumer viewpoint were held, favoring the policy of varicella zoster virus vaccination at infancy.