UPMC Université Paris 06, UMRS 707, Paris, France.
PLoS One. 2011 May 10;6(5):e19621. doi: 10.1371/journal.pone.0019621.
In this study, we assess how effective pandemic and trivalent 2009-2010 seasonal vaccines were in preventing influenza-like illness (ILI) during the 2009 A(H1N1) pandemic in France. We also compare vaccine effectiveness against ILI versus laboratory-confirmed pandemic A(H1N1) influenza, and assess the possible bias caused by using non-specific endpoints and observational data.
We estimated vaccine effectiveness by using the following formula: VE = (PPV-PCV)/(PPV(1-PCV)) × 100%, where PPV is the proportion vaccinated in the population and PCV the proportion of vaccinated influenza cases. People were considered vaccinated three weeks after receiving a dose of vaccine. ILI and pandemic A(H1N1) laboratory-confirmed cases were obtained from two surveillance networks of general practitioners. During the epidemic, 99.7% of influenza isolates were pandemic A(H1N1). Pandemic and seasonal vaccine uptakes in the population were obtained from the National Health Insurance database and by telephonic surveys, respectively. Effectiveness estimates were adjusted by age and week. The presence of residual biases was explored by calculating vaccine effectiveness after the influenza period. The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after. It was 86% (56-98) against confirmed influenza. The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after. It was 60% (41-74) against confirmed influenza.
The effectiveness of pandemic vaccines in preventing confirmed pandemic A(H1N1) influenza on the field was high, consistently with published findings. It was significantly lower against ILI. This is unsurprising since not all ILI cases are caused by influenza. Trivalent 2009-2010 seasonal vaccines had a statistically significant effectiveness in preventing ILI and confirmed pandemic influenza, but were not better in preventing confirmed pandemic influenza than in preventing ILI. This lack of difference might be indicative of selection bias.
本研究评估了大流行疫苗和三价 2009-2010 季节性疫苗在法国 2009 年甲型 H1N1 流感大流行期间预防流感样疾病（ILI）的有效性。我们还比较了疫苗对 ILI 与实验室确诊的大流行甲型 H1N1 流感的有效性，并评估了使用非特异性终点和观察数据可能导致的偏倚。
我们使用以下公式估计疫苗的有效性：VE = （PPV-PCV）/（PPV(1-PCV)）×100%，其中 PPV 是人群中接种疫苗的比例，PCV 是接种疫苗的流感病例比例。人们在接种一剂疫苗后三周被认为已接种疫苗。ILI 和大流行甲型 H1N1 实验室确诊病例分别来自两个全科医生监测网络。在流行期间，99.7%的流感分离株为大流行甲型 H1N1。人群中流感大流行和季节性疫苗接种率分别从国家健康保险数据库和电话调查中获得。通过按年龄和周进行调整，对有效性估计值进行了调整。通过在流感期后计算疫苗的有效性来探索是否存在残余偏差。流感大流行期间，大流行疫苗预防 ILI 的有效性为 52%（95%置信区间：30-69），之后为 33%（4-55）。它对确诊流感的有效性为 86%（56-98）。流感大流行期间，季节性疫苗预防 ILI 的有效性为 61%（56-66），之后为 19%（-10-41）。它对确诊流感的有效性为 60%（41-74）。
大流行疫苗在现场预防确诊的大流行甲型 H1N1 流感的有效性很高，与已发表的结果一致。它对 ILI 的有效性显著降低。这并不奇怪，因为并非所有 ILI 病例都是由流感引起的。三价 2009-2010 季节性疫苗在预防 ILI 和确诊大流行流感方面具有统计学意义上的有效性，但在预防确诊大流行流感方面并不优于预防 ILI。这种差异可能表明存在选择偏差。
