对戊性肝炎疫苗评价的研究设计，把题目翻译成英文流行病学题目，给出数据分析方法

Title: Assessment of the efficacy of Hepatitis E virus vaccine: A randomized controlled trial

Objective: To evaluate the efficacy of Hepatitis E virus vaccine in preventing Hepatitis E infection among individuals at risk of contracting the disease.

Study design: This study will be a randomized controlled trial involving two groups: the intervention group and the control group. The intervention group will receive the Hepatitis E virus vaccine, while the control group will receive a placebo. Participants will be followed up for a period of 12 months to assess the incidence of Hepatitis E infection.

Participants: The study will involve individuals who are at risk of contracting Hepatitis E infection, such as healthcare workers, individuals living in endemic areas, and individuals with chronic liver disease.

Data analysis: The primary outcome measure will be the incidence of Hepatitis E infection in both groups. The incidence rate ratio (IRR) will be calculated to compare the incidence rate of Hepatitis E infection between the intervention and control groups. A multivariate Cox regression analysis will be performed to assess the adjusted hazard ratio (HR) of Hepatitis E infection between the two groups, adjusting for confounding factors such as age, sex, and underlying liver disease. A sub-group analysis will also be conducted to assess the efficacy of the vaccine in different sub-populations.