One dose of the pandemic flu vaccines used in seven European countries conferred good protection against pandemic H1N1 influenza in the 2009-10 season, especially in people aged less than 65 years and in those without any chronic diseases. These findings from a study funded by the European Centre for Disease Prevention and Control (ECDC) and coordinated by EpiConcept, Paris, France, published in this week's PLoS Medicine, give an indication of the vaccine effectiveness for the influenza A (H1N1) 2009 strain included in the 2010-11 seasonal vaccines.
The authors conducted a multi-centre case-control study based on practitioner surveillance networks from seven countries -- France, Hungary, Ireland, Italy, Romania, Portugal and Spain. Patients consulting a participating practitioner for influenza-like-illness had a nasal or throat swab taken within eight days of symptom onset. Individuals were considered vaccinated if they had received a dose of the vaccine more than 14 days before the date of onset of influenza like illness and unvaccinated if they were not vaccinated at all or if the vaccine was given less than 15 days before the onset of symptoms.
The authors analysed pandemic influenza vaccination effectiveness in those vaccinated less than 8 days, those vaccinated between, and including, 8 and 14 days and those vaccinated more than 14 days before onset of symptoms compared to those who had never been vaccinated. The authors then used statistical models to measure the effectiveness of pandemic influenza vaccine according to three age groups (< 15, 15-64, and 65+ years of age) and the presence of chronic diseases. These results obtained during the late phase of the pandemic suggest good protection with the pandemic H1N1 vaccine (vaccine effectiveness estimates between 65% and 100%). The findings also suggest that the 2009-10 seasonal influenza vaccine (as opposed to the pandemic H1N1 vaccine) did not protect against pandemic H1N1 influenza illness.
The authors said: "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." They added: "Future studies should include estimation of effectiveness of the new trivalent vaccine in the 2010-2011 season, when vaccination will occur before the influenza season starts."
Bruno C. Ciancio, senior influenza expert from ECDC -- who conceived the idea of a European network to measure influenza vaccine effectiveness and collaborated to design the study- stressed: "This study showed the added value of collaboration at European level as concerns vaccine evaluation. In addition, the results obtained are especially important for European countries this season, considering that the predominant influenza strain currently circulating across Europe is influenza A (H1N1).''
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