Reduced efficacy from repeat flu vaccination depends on vaccine type, strain
Repeat immunization with inactivated influenza vaccine appears to reduce children’s antibody responses to influenza strains A(H1N1)pdm09 and B, according to findings published in the Journal of the Pediatric Infectious Diseases Society. The effect of previous-season vaccination on the efficacy of live-attenuated influenza vaccine was less clear, researchers said.
Previous research has shown waning protection from influenza vaccine in patients who had been vaccinated during the previous season, but findings recently published in Annals of Family Medicine showed that repeat immunization with IIV appeared to increase long-term protection against some respiratory illness episodes in children with pre-existing medical conditions.
“The few studies that have examined the effect of repeated annual vaccination on influenza vaccine effectiveness (VE) in children found that VE was modified by their previous-season vaccination status and that the effect of previous-season vaccination history varied according to the vaccine type received,” Huong Q. McLean, PhD, MPH, a research scientist at the Marshfield Clinic Research Institute’s Center for Clinical Epidemiology and Public Health, and colleagues wrote.
McLean and colleagues examined the association between previous vaccination history and hemagglutination-inhibition antibody titers in children (n = 267) vaccinated during three influenza seasons: 2013-2014, 2014-2015 and 2015-2016.
Results showed that the geometric mean fold rise (GMFR) — a measure of the increase in geometric mean titers (GMTs) after vaccination — was significantly lower in previous-season IIV recipients (1.5 to 2.3) than in children who were unvaccinated or received LAIV in the previous season (4.3 to 12.9) for influenza strains A(H1N1)pdm09 and influenza B. The same findings were less pronounced for influenza A(H3N2) — a strain that had caused a severe influenza season in the United States last year.
According to the researchers, most children had a post-IIV vaccination titer of 40 or more for vaccine strains in all seasons, regardless of previous-season vaccination history. Little or no increase in antibody levels was observed after children had been vaccinated with LAIV.
“The difference in response following vaccination was not consistent across vaccine strains and seasons,” McLean told Infectious Diseases in Children.
McLean said “additional studies are needed to better understand the variation in response and any age cohort effects.” – by Katherine Bortz
Disclosures: The authors report no relevant financial disclosures.