The vaccine for pandemic 2009 H1N1 influenza was about 72% effective across seven European countries, according to findings from a case-control study published Jan. 11 in PLoS Medicine.
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The vaccine for pandemic 2009 H1N1 influenza was about 72% effective across seven European countries, according to findings from a case-control study.
"The results of this study provide early estimates of the pandemic influenza vaccine effectiveness suggesting that the monovalent pandemic vaccines have been effective. The findings also give an indication of the vaccine effectiveness" for the influenza A (H1N1) 2009 strain included in the 2010-2011 seasonal vaccines, although specific vaccine effectiveness studies will have to be conducted to verify if similar rates of effectiveness are observed with 2010-2011 trivalent vaccines, Marta Valenciano, a veterinarian and epidemiologist at EpiConcept, Paris, and colleagues wrote in an accompanying summary of the study.
The study involved 2,902 patients with influenzalike illnesses (ILI) from France, Hungary, Ireland, Italy, Portugal, Romania, and Spain during the 2009-2010 season. All had throat swabs fewer than 8 days after the onset of symptoms. Among those patients, roughly 32% tested positive for pandemic H1N1. Investigators compared these confirmed H1N1 cases to patients with ILI who tested negative for any influenza virus.
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Overall, 7% of all the patients – ranging from 0% in Italy to 29% in Hungary – had received at least one dose of the H1N1 vaccine more than 14 days before symptom onset.
The investigators adjusted their effectiveness results for confounding factors, including age; sex; presence and severity of chronic conditions; pregnancy; obesity; smoking history; number of practitioner visits in the preceding 12 months; use of influenza antivirals; and seasonal influenza vaccination during the previous two seasons.
As expected, vaccines that were delivered fewer than 8 days before the onset of ILI symptoms showed a relatively low adjusted effectiveness rate (19%), compared with 67% among those who were vaccinated more than 14 days before symptom onset.
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The investigators also found that the 2009-2010 seasonal influenza vaccine was only 9.9% effective against H1N1 (PLoS Med. 2011 Jan. 11 [doi:10.1371/journal.pmed.1000388]).
The results of this study should be interpreted with caution because of limitations in the pandemic context (such as late timing of the studies, low incidence, and low vaccine coverage leading to imprecise estimates) and potential biases because of the study design, confounding factors, and missing values. The researchers recommended that, in the future, the sample size per country be enlarged in order to allow for precise pooled and stratified analyses.
Among the 19 authors of the study, several disclosed relationships with various pharmaceutical companies and European government agencies. The European Centre for Disease Prevention and Control funded the study.
Other influenza-related reports included the following:
• The U.K. Department of Health has warned physicians to watch for bacterial coinfections in patients with influenza. According to a Jan. 13 report in Pulse, an online newsletter for general practitioners, a "number of data sources suggest recent increases in some bacterial infections, particularly invasive Group A streptococcal infection and meningococcal disease." The report urged physicians to start antiviral and antibiotic treatment as soon as possible, when appropriate.
• According to a U.S. Centers for Disease Control and Prevention report, as of Jan. 1, ILI activity was high in Alabama, Georgia, Illinois, Louisiana, Mississippi, Oklahoma, and New York City; moderate in Nevada and New Jersey; and minimal to low in the rest of the country.
• Of 4,911 specimens from people with ILI, 20.3% tested positive for influenza, according to a CDC weekly report. Among those, 34.1% proved to be influenza B, and 65.9% were influenza A. No subtyping was performed in 52.3% of the influenza A samples, 41% were subtype A(H3), and 6.7% were A(2009 H1N1).
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