WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
Department of Paediatrics and Adolescent Medicine, Queen Mary Hospital and Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
Lancet Respir Med. 2018 Dec;6(12):925-934. doi: 10.1016/S2213-2600(18)30419-3. Epub 2018 Nov 12.
The protection conferred by influenza vaccination is generally thought to last less than a year, necessitating annual revaccination. However, the speed with which influenza vaccine effectiveness might decline during a year is unknown, which is of particular importance for locations with year-round influenza activity. We aimed to assess how influenza vaccine effectiveness changes by time intervals between vaccination and admission to hospital, taking advantage of almost year-round circulation of influenza in Hong Kong.
In this test-negative case-control study, we analysed vaccine effectiveness in children (aged 6 months to 17 years) who were admitted to hospital in Hong Kong over 5 consecutive years (2012-17). We included those who were admitted to general wards in four public hospitals in Hong Kong with a fever (≥38°C) and any respiratory symptom, such as runny nose, cough, or sore throat. We used direct immunofluorescence assay and reverse transcription PCR to detect influenza virus infection, and recorded children's influenza immunisation history. We compared characteristics of positive cases and negative controls and examined how vaccine effectiveness changed by time between vaccination and admission to hospital with regression analyses.
Between Sept 1, 2012, and Aug 31, 2017, we enrolled 15 695 children hospitalised for respiratory infections, including 2500 (15·9%) who tested positive for influenza A or B and 13 195 (84·1%) who tested negative. 159 (6·4%) influenza-positive cases and 1445 (11·0%) influenza-negative cases had been vaccinated. Most vaccinations were done by December of each influenza vaccination season. Influenza-related admissions to hospital occurred year-round, with peaks in January through March in most years and a large summer peak in 2016; pooled vaccine effectiveness for children of all ages was 79% (95% CI 42-92) for September to December, 67% (57-74) for January to April, and 43% (25-57) for May to August. Vaccine effectiveness against influenza A or B was estimated as 79% (95% CI 64-88) within 0·5-2 months of vaccination, 60% (46-71) within >2-4 months, 57% (39-70) within >4-6 months, and 45% (22-61) within >6-9 months. In separate analyses by type and subtype, we estimated that vaccine effectiveness declined by 2-5 percentage points per month.
Influenza vaccine effectiveness decreased during the 9 months after vaccination in children in Hong Kong. Our findings confirm the importance of annual vaccination in children. Influenza vaccines that provide broader and longer-lasting protection are needed to provide year-round protection in regions with irregular influenza seasonality or lengthy periods of influenza activity.
Health and Medical Research Fund, Hong Kong and the Research Grants Council, Hong Kong.
人们普遍认为流感疫苗的保护作用持续时间不足一年，因此需要每年进行加强免疫接种。然而，流感疫苗的有效性在一年内下降的速度尚不清楚，这对于全年都有流感活动的地区尤为重要。我们旨在评估在香港，流感疫苗有效性随接种疫苗和住院时间间隔的变化情况，利用香港几乎全年都有流感循环的优势。
在这项病例对照的巢式病例研究中，我们分析了在香港连续 5 年（2012-17 年）住院的儿童（6 个月至 17 岁）的疫苗有效性。我们纳入了在香港 4 家公立医院普通病房住院、体温（≥38°C）伴有任何呼吸道症状（如流鼻涕、咳嗽或喉咙痛）的患者。我们使用直接免疫荧光测定法和逆转录聚合酶链反应来检测流感病毒感染，并记录了儿童的流感免疫史。我们比较了阳性病例和阴性对照的特征，并通过回归分析研究了疫苗有效性随接种疫苗和住院时间间隔的变化情况。
在 2012 年 9 月 1 日至 2017 年 8 月 31 日期间，我们纳入了 15695 名因呼吸道感染住院的儿童，其中 2500 名（15.9%）流感 A 或 B 检测呈阳性，13195 名（84.1%）检测呈阴性。159 名（6.4%）流感阳性病例和 1445 名（11.0%）流感阴性病例已接种疫苗。大多数疫苗接种是在当年 12 月完成的。流感相关住院发生在全年，大多数年份的 1 月至 3 月为高峰期，2016 年夏季出现一个大高峰；所有年龄段儿童的疫苗总体有效性为 9 月至 12 月 79%（95%CI 42-92），1 月至 4 月 67%（57-74），5 月至 8 月 43%（25-57）。流感 A 或 B 的疫苗有效性估计为接种后 0.5-2 个月内 79%（95%CI 64-88），2-4 个月内 60%（46-71），4-6 个月内 57%（39-70），6-9 个月内 45%（22-61）。按病毒类型和亚型进行的单独分析估计，疫苗有效性每月下降 2-5 个百分点。
在香港儿童中，流感疫苗接种后 9 个月内其有效性逐渐降低。我们的发现证实了在儿童中每年接种疫苗的重要性。需要提供更广泛和更持久保护作用的流感疫苗，以在季节性不规则或流感活动时间较长的地区提供全年保护。
香港卫生署和香港研究资助局。
