Study notes lower immune response after 2 straight flu vaccinations
Post-vaccine levels of antibodies to influenza hemagglutinin (HA) and neuraminidase (NA) decline slowly over 18 months in adults, and individuals vaccinated 2 years in a row have significantly lower immune responses, according to a study yesterday in the Journal of Infectious Diseases.
University of Michigan researchers analyzed data from 941 adults 18 to 49 years old who participated in the second and third years of a previously published randomized controlled trial conducted during the 2005-06 and 2006-07 flu seasons on the efficacy of trivalent inactivated vaccine (TIV) and live-attenuated influenza vaccine (LAIV). They examined blood specimens taken just before vaccination and at 1, 6, 12, and 18 months after vaccination.
They found that HA inhibition (HAI) and NA inhibition (NAI) titers decreased slowly and minimally over 18 months and estimated it would take on average about 600 days (20 months) for a two-fold antibody titer decrease. The rate of decline was faster in TIV recipients, but those recipients achieved much higher post-vaccination HAI and NAI titers. And titers of TIV recipients remained significantly higher than LAIV recipients or placebo recipients after 18 months.
The investigators also found that both TIV and LAIV recipients vaccinated 2 consecutive years had significantly lower HAI titers following vaccination in the second year, although the rates of antibody decline were similar to those not vaccinated 2 years running.
The authors conclude that, even though antibodies remain high over multiple seasons, antigenic drift of circulating strains may necessitate annual vaccination. They add that, even though HAI response to immunization may be impaired with back-to-back vaccinations, it is still higher than with a placebo, even after 18 months.
Read more @http://www.cidrap.umn.edu/news-perspective/2015/05/news-scan-may-27-2015