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Public Health Ontario, 480 University Avenue, Suite 300, Toronto, Ontario M5G 1V2, Canada.
Vaccine. 2019 Nov 20;37(49):7213-7232. doi: 10.1016/j.vaccine.2019.09.086. Epub 2019 Oct 22.
Influenza causes significant annual morbidity and mortality, particularly in older adults, for whom influenza vaccine effectiveness (VE) is also lower. Immunizing one group (e.g., children) against influenza may indirectly protect another group (e.g., older adults) against influenza and its complications.
We updated previous systematic reviews on indirect protection against influenza by searching MEDLINE and EMBASE for relevant human studies published until January 4, 2017. We abstracted and critically appraised English language publications that reported or provided information to calculate indirect VE against influenza, as a percentage, in non-institutional settings. We developed a term called 'estimated actual protection' to explore the relationship between indirect protection and the product of direct VE and relative vaccine coverage. We calculated estimated actual protection for a subset of studies that reported coverage and indirect VE for: laboratory-confirmed influenza; outpatient care for respiratory illness; influenza-associated emergency visits; or influenza-associated hospitalizations. We ran linear mixed models to compare estimated actual protection against indirect VE for the four outcomes, and graphed the data.
Of 2320 unique records identified, we abstracted and appraised 26 articles describing 24 studies. The majority of included studies reported at least one outcome suggesting that immunizing one group reduced influenza-related outcomes in another group. Critical appraisal of the abstracted studies identified recurring methodological weaknesses, such as lack of laboratory-confirmed influenza. Our exploratory analyses of 18 studies indicated a positive but not statistically significant relationship between estimated actual protection and indirect protection for each of the four outcomes.
Our systematic review and exploratory analyses suggest influenza immunization provides some level of indirect protection. However, our critical appraisal highlights the need for a standardized and consistently applied approach to measuring indirect protection against influenza to fill existing knowledge gaps. Additionally, the concept of estimated actual protection requires validation.
流感每年都会导致大量发病和死亡，尤其是老年人，流感疫苗的有效性（VE）也较低。对一组人群（如儿童）进行流感免疫可能会间接保护另一组人群（如老年人）免受流感及其并发症的影响。
我们通过检索 MEDLINE 和 EMBASE 中截至 2017 年 1 月 4 日的相关人类研究，更新了之前关于流感间接保护的系统评价。我们摘录并批判性评价了以英文发表的报告或提供信息以计算非机构环境中针对流感的间接 VE（以百分比表示）的研究。我们开发了一个术语“估计实际保护”来探索间接保护与直接 VE 和相对疫苗覆盖率的乘积之间的关系。我们对报告了覆盖率和针对：实验室确诊流感、门诊呼吸道疾病治疗、流感相关急诊就诊或流感相关住院治疗的间接 VE 的部分研究计算了估计实际保护。我们对四个结局进行了线性混合模型比较，并绘制了数据。
在 2320 个唯一记录中，我们摘录并评价了 26 篇文章，共描述了 24 项研究。大多数纳入的研究报告了至少一个结果，表明对一组人群进行免疫接种可降低另一组人群的流感相关结局。对摘录研究的批判性评价发现了一些反复出现的方法学弱点，例如缺乏实验室确诊的流感。我们对 18 项研究的探索性分析表明，对于四个结局中的每一个，估计实际保护和间接保护之间存在正相关关系，但无统计学意义。
我们的系统评价和探索性分析表明流感免疫接种提供了一定程度的间接保护。然而，我们的批判性评价强调需要采用标准化和一致的方法来衡量针对流感的间接保护，以填补现有知识空白。此外，估计实际保护的概念需要验证。
