ba Valenciano 2011.

Methods	A multicentre case‐control study based on sentinel practitioner surveillance networks from 7 European countries was undertaken to estimate the effectiveness of 2009–10 pandemic and seasonal influenza vaccines against medically attended ILI laboratory confirmed as pandemic influenza A (H1N1) (pH1N1).   The study was conducted within the context of the existing European Influenza Surveillance Network (EISN). At the 7 study sites, EISN sentinel primary care practitioners were invited to participate in the study. In Portugal and Italy, practitioners other than those participating in EISN were also invited to participate.   The study population consisted of patients consulting a participating practitioner for ILI (6 sites) or ARI (France) and having a nasal or throat swab taken within an interval of less than 8 days after symptom onset.   In Hungary, the study population was restricted to patients aged more than 17 years. In Italy, the study population was restricted to patients who belonged to the groups for which the pandemic vaccine was recommended.   In 5 of the 7 study sites, practitioners used a systematic random sample to select the patients to swab. In Ireland, each participating practice was asked to take a nasal or throat swab from 5 patients presenting with ILI each week.   In France, each practitioner had an age group assigned and swabbed the first ARI patient of the week in the allocated age group.
Participants	Exclusion criteria Individuals who tested positive for influenza A but had a non‐typeable strain, those testing positive for other strains of influenza A or for influenza B, and those with missing information on laboratory results were excluded. Description of cases A case of pandemic influenza A (H1N1) 2009 (pH1N1 case) was an ILI patient (defined according to the EU case definition as sudden onset of symptoms and at least 1 of the following 4 systemic symptoms: fever or feverishness, malaise, headache, myalgia, and at least 1 of the following 3 respiratory symptoms: cough, sore throat, shortness of breath) who was swabbed and tested positive for the pH1N1 using real‐time PCR or culture.   Swabs were tested for influenza at the respective countries’ National Influenza Reference Laboratory. In France, Italy, and Spain, tests were also conducted in other laboratories participating in the National Influenza Sentinel Surveillance System. Description of controls Controls were ILI patients who were swabbed and tested negative for any influenza virus.
Interventions	Exposure For pandemic and seasonal influenza vaccine, individuals were considered vaccinated if they had received a dose of the vaccine more than 14 days before the date of onset of ILI symptoms and UV if they had received no vaccine or the vaccine was given less than 15 days before the onset of ILI symptoms. Vaccination status was ascertained using the practitioners’ medical records or during the patient interview. Each of the 7 study teams entered and validated data. Validation of the vaccination status and of other variables was attempted by contacting the practitioner or by checking existing vaccination registries in the case of missing information.
Outcomes	pH1N1 using real‐time PCR or culture
Funding Source	Government
Notes	The authors conclude that the results suggest good protection of the pandemic monovalent vaccine against medically attended pH1N1 and no effect of the 2009–10 seasonal influenza vaccine. "However, the late availability of the pandemic vaccine and subsequent limited coverage with this vaccine hampered our ability to study vaccine benefits during the outbreak period." Future studies should include estimation of the effectiveness of the new trivalent vaccine in the upcoming 2010–11 season, when vaccination will occur before the influenza season starts.
Risk of bias
Bias	Authors' judgement	Support for judgement
CC‐Case Selection	Low risk	Independent validation
CC‐Control Selection	Low risk	Drawn from the same population
CC‐Comparability	Low risk	Adjustment by confounders
CC‐Exposure	Low risk	Interview
Summary assessments	Low risk	Possible underestimation of vaccine efficacy