Biological Risks Unit, Institut National de Santé Publique du Québec, Quebec City, Quebec, Canada.
Faculty of Medicine, Laval University, Quebec City, Quebec, Canada.
Clin Infect Dis. 2024 Mar 20;78(3):765-774. doi: 10.1093/cid/ciad627.
Influenza immunization programs aim to reduce the risk and burden of severe outcomes. To inform optimal program strategies, we monitored influenza hospitalizations over 7 seasons, stratified by age, comorbidity, and vaccination status.
We assembled data from 4 hospitals involved in an active surveillance network with systematic collection of nasal samples and polymerase chain reaction testing for influenza virus in all patients admitted through the emergency department with acute respiratory infection during the 2012-2013 to 2018-2019 influenza seasons in Quebec, Canada. We estimated seasonal, population-based incidence of influenza-associated hospitalizations by subtype predominance, age, comorbidity, and vaccine status, and derived the number needed to vaccinate to prevent 1 hospitalization per stratum.
The average seasonal incidence of influenza-associated hospitalization was 89/100 000 (95% confidence interval, 86-93), lower during A(H1N1) (49-82/100 000) than A(H3N2) seasons (73-143/100 000). Overall risk followed a J-shaped age pattern, highest among infants 0-5 months and adults ≥75 years old. Hospitalization risks were highest for children <5 years old during A(H1N1) but for highest adults aged ≥75 years during A(H3N2) seasons. Age-adjusted hospitalization risks were 7-fold higher among individuals with versus without comorbid conditions (214 vs 30/100 000, respectively). The number needed to vaccinate to prevent hospitalization was 82-fold lower for ≥75-years-olds with comorbid conditions (n = 1995), who comprised 39% of all hospitalizations, than for healthy 18-64-year-olds (n = 163 488), who comprised just 6% of all hospitalizations.
In the context of broad-based influenza immunization programs (targeted or universal), severe outcome risks should be simultaneously examined by subtype, age, comorbidity, and vaccine status. Policymakers require such detail to prioritize promotional efforts and expenditures toward the greatest and most efficient program impact.
流感免疫计划旨在降低严重后果的风险和负担。为了为最佳计划策略提供信息，我们监测了 7 个季节的流感住院情况，按年龄、合并症和疫苗接种状态进行分层。
我们从参与主动监测网络的 4 家医院收集数据，该网络系统地收集所有通过急诊部门入院的急性呼吸道感染患者的鼻样本，并进行聚合酶链反应检测流感病毒。在加拿大魁北克省，2012-2013 至 2018-2019 流感季节期间，我们根据亚型优势、年龄、合并症和疫苗接种状态估计了季节性、基于人群的流感相关住院率，并得出了每接种一个人预防一个住院治疗所需的人数。
流感相关住院的平均季节性发病率为 89/100000（95%置信区间，86-93），A（H1N1）季节（49-82/100000）低于 A（H3N2）季节（73-143/100000）。总体风险呈 J 形年龄模式，0-5 个月的婴儿和≥75 岁的成年人最高。A（H1N1）季节，<5 岁的儿童住院风险最高，而 A（H3N2）季节，最高风险为≥75 岁的成年人。有合并症的个体与无合并症的个体的年龄调整住院风险分别为 214 比 30/100000（分别）。有合并症的≥75 岁人群接种疫苗预防住院的人数（n=1995）比健康的 18-64 岁人群（n=163488）低 82 倍，而前者占所有住院人数的 39%，后者仅占所有住院人数的 6%。
在广泛的流感免疫计划（有针对性或普遍）的背景下，应根据亚型、年龄、合并症和疫苗接种状态同时检查严重后果风险。政策制定者需要这些详细信息来优先考虑宣传工作和支出，以实现最大和最有效的计划影响。
