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Immunity from inactivated seasonal influenza vaccine decreased after one year
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Protection against influenza acquired through trivalent inactivated influenza vaccine dwindled a year after vaccination, according to study findings in Clinical Infectious Diseases.
Benjamin J. Cowling, PhD, of the University of Hong Kong, and colleagues conducted a randomized study of 484 children aged 5 to 17 years in Hong Kong. Children received either trivalent inactivated influenza vaccine or placebo from September 2009 through January 2010. Study participants were followed for 3 years; researchers collected sera, symptom diaries, and nose and throat swabs when participants or their household member were ill.
Benjamin J. Cowling
Five influenza epidemics occurred during the study period: H1N1pdm09 in the winter of 2010; H3N2 in the summer of 2010; the second wave of H1N1pdm09 in the winter of 2011; influenza B in the winter of 2012; and H3N2 in the spring and summer of 2012.
The researchers reported that the first wave of H1N1pdm09 was strongly associated with children; incidence of infection among those unvaccinated was 59%. Vaccinated children had a lower risk for infection during that particular epidemic.
Incidence of infection among unvaccinated children was 7% during the H3N2 epidemic in 2010; 14% during the H1N1pdm09 epidemic in 2011; 20% during the influenza B epidemic in 2012; and 31% during the H3N2 epidemic in 2012.
Children who developed H1N1pdm09 or H3N2 in 2009 or 2010 were more likely to be protected from these infections during future epidemics. Seven percent of children with H1N1pdm09 during the first wave had evidence of re-infection during the second wave; 22% of children with H3N2 in 2010 had evidence of re-infection in 2012. Children who developed H1N1pdm09 in 2009 or 2010 had an increased risk for H3N2 infection in 2012.
Researchers found no evidence of heterotypic or heterosubtypic protection against infection.
“Our results indicate that there was little continued protection afforded by [trivalent inactivated influenza vaccine] beyond a year after vaccination…We did not identify any evidence for heterotypic or heterosubtypic immunity against infection, but epidemics did not occur very close together in our study,” the researchers concluded.
Disclosure: For a full list of disclosures, see the study.
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