Sebastian R, Skowronski D M, Chong M, Dhaliwal J, Brownstein J S
Epidemiology Services, British Columbia Centre for Disease Control, 655 12th Avenue West, Vancouver, British Columbia, V5Z 4R4 Canada.
Vaccine. 2008 Mar 4;26(10):1397-403. doi: 10.1016/j.vaccine.2007.11.090. Epub 2007 Dec 26.
The influenza immunization program in North America has been primarily designed to provide direct benefit to vaccinated individuals at highest risk of serious influenza outcomes. Some evidence suggests that immunization of certain age groups may also extend indirect protective benefit to vulnerable populations. Our goal was to identify age groups associated earliest with seasonal influenza activity and who may have the greatest indirect impact at the population level. We examined age-based associations between influenza medical visits and population-wide hospitalization/mortality due to pneumonia & influenza (P&I) using administrative datasets in British Columbia, Canada. A peak week was identified for each age group based on the highest rates observed in a given week for that study year. Mean rates at the peak week were averaged over the study years per age group. Timeliness (T) was defined as the mean difference in days between the first peak in influenza medical visits and population-wide P&I hospitalizations/deaths. Poisson regression was applied to calculate prediction (Pr) as the average proportion of deviance in P&I explained by influenza medical visits. T and Pr were derived by age group, and the product (T x Pr) was used as a summary measure to rank potential indirect effects of influenza by age group. Young children (0-23 months) and the elderly (> or = 65 years) had the highest peak rates of P&I hospitalization. Children < 6m and the elderly had the highest peak rates of P&I mortality. We found no significant differences by age for influenza medical visits in predicting population-wide P&I hospitalizations or deaths. School-aged children (5-19 years) showed the best relative combination of T x Pr, followed by preschool-aged children (2-4 years). We conclude that the very young and old suffer the greatest morbidity due to P&I, and an indirect role for school-aged children in anticipating the risk to others warrants further evaluation.
北美流感免疫计划的主要目的是为面临严重流感后果风险最高的接种个体提供直接益处。一些证据表明，对某些年龄组进行免疫接种也可能为弱势群体带来间接保护益处。我们的目标是确定最早与季节性流感活动相关且在人群层面可能产生最大间接影响的年龄组。我们利用加拿大不列颠哥伦比亚省的行政数据集，研究了流感就诊与因肺炎和流感（P&I）导致的全人群住院/死亡率之间基于年龄的关联。根据给定研究年份中某一周观察到的最高发病率，为每个年龄组确定一个高峰周。将各年龄组在高峰周的平均发病率在各研究年份进行平均。及时性（T）定义为流感就诊首次高峰与全人群P&I住院/死亡之间天数的平均差异。应用泊松回归计算预测值（Pr），即流感就诊所解释的P&I偏差的平均比例。T和Pr按年龄组得出，其乘积（T×Pr）用作按年龄组对流感潜在间接影响进行排名的汇总指标。幼儿（0 - 23个月）和老年人（≥65岁）的P&I住院高峰发病率最高。6个月以下儿童和老年人的P&I死亡率高峰发病率最高。我们发现，在预测全人群P&I住院或死亡方面，流感就诊在不同年龄之间没有显著差异。学龄儿童（5 - 19岁）的T×Pr相对组合最佳，其次是学龄前儿童（2 - 4岁）。我们得出结论，幼儿和老年人因P&I遭受的发病率最高，学龄儿童在预测他人风险方面的间接作用值得进一步评估。
