A new study finds that the 2009 H1N1 flu vaccines performed very well, especially for older children and nonelderly adults.
A new study finds that the 2009 H1N1 flu vaccines performed very well, especially for older children and nonelderly adults. The study was published online last week in the journal PLoS ONE.
To measure the effectiveness of the four H1N1 flu vaccines that were made available in the US in response to the pandemic virus that emerged in April 2009, researchers studied patients treated for respiratory illness between September 2009 and May 2010 at selected clinics in Wisconsin, Michigan, New York, and Tennessee. In all, 6,757 patients provided respiratory specimens, which were tested for the 2009 H1N1 virus.
The virus was detected in 15% (1,011) of the patients, of which 1% (15) had been vaccinated more than two weeks before the onset of symptoms. Of those who tested negative for the virus, 18% had received the vaccine more than two weeks before they got sick.
Three of the four available vaccines contained inactivated virus, while one contained live attenuated virus. The inactivated vaccine had an effectiveness of 89% in patients aged 10 to 49, though it was not found to be effective for those under 10 or over 50. (One reason for the ineffectiveness in children is that two doses of vaccine were recommended for them, and most had received just one.) However, the live attenuated vaccine was 82% effective in children aged two to nine years, even when received just a week before the onset of symptoms.