MMWR Morb Mortal Wkly Rep. 2009 Apr 3;58(12):312.
The influenza season in temperate climates extends from October through March in the northern hemisphere and from April through September in the southern hemisphere. Recent studies indicate that influenza viruses can circulate throughout the year in the tropics and that influenza is the most frequently acquired vaccine-preventable disease among those traveling to tropical and subtropical countries. Influenza outbreaks have been reported among persons who travel from the northern hemisphere to the southern hemisphere and among persons from the northern hemisphere on group tours. To reduce the risk for influenza during travel, the Advisory Committee on Immunization Practices (ACIP) recommends that persons from the northern hemisphere who are recommended for annual vaccination or who want to avoid influenza illness but have not yet received the 2008--09 influenza vaccine should consider being vaccinated 1) before travel to the southern hemisphere during influenza season, 2) before travel to the tropics at any time of year, or 3) when traveling as part of a tour group that includes persons from areas where influenza circulates during April--September (e.g., the southern hemisphere). Vaccine formulations for each hemisphere are updated yearly but might differ according to virus surveillance information from each hemisphere.
温带气候地区的流感季节在北半球是从10月持续到次年3月，在南半球是从4月持续到9月。最近的研究表明，流感病毒在热带地区可全年传播，而且在前往热带和亚热带国家的人群中，流感是最常见的可通过接种疫苗预防的疾病。据报道，从北半球前往南半球的旅行者以及参加团体旅行的北半球人群中都出现了流感疫情。为降低旅行期间感染流感的风险，免疫实践咨询委员会（ACIP）建议，北半球那些被推荐每年接种疫苗或希望避免感染流感但尚未接种2008-2009年度流感疫苗的人群，应考虑在以下情况下接种疫苗：1）在流感季节前往南半球旅行前；2）在一年中的任何时候前往热带地区前；或3）作为旅行团的一员旅行时，该旅行团中有来自4月至9月流感流行地区（如南半球）的人员。每个半球的疫苗配方每年都会更新，但可能会根据每个半球的病毒监测信息有所不同。
