September 22, 2017
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LAIV ineffective for children during 2015-2016 season

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Although vaccination against influenza lessened the chances of illness, the live-attenuated vaccine demonstrated inefficacy and the inactivated vaccine demonstrated significant effectiveness in children for the 2015-2016 season, according to a study published in The New England Journal of Medicine.

“The effectiveness of influenza vaccination and the corresponding effect of vaccination programs on the burden of influenza can vary considerably from year to year,” Michael L. Jackson, PhD, from the Kaiser Permanente Washington Health Research Institute, and colleagues wrote. “In light of this variability, annual observational studies of influenza vaccine effectiveness are critical as ongoing evaluations of the value of influenza vaccination programs, as well as for identifying problems with licensed influenza vaccines.”

To assess the impact of changing the A(H1N1)pdm09 virus strain in the live-attenuated influenza vaccine (LAIV) and the effectiveness of this strain in 2015-2016, the researchers conducted a study in which children 6 months and older with acute respiratory illness were recruited from ambulatory care clinics throughout the United States. They then projected vaccine effectiveness using a test-negative design, with independent estimates made for inactivated vaccines and the LAIV.

Of the 6,879 children included in the study, 19% had confirmed influenza. The most frequently observed strains were A(H1N1)pdm09, with 11% of participants testing positive, and influenza B, with 7% testing positive. Vaccination was able to provide protection against 48% of all influenza-related illness (95% CI, 47-70; P < .001).

The inactivated vaccine was 60% effective against influenza in children between the ages of 2 and 17 years (95% CI, 47-70; P < .001); however, the LAIV demonstrated inefficacy at 5% (95% CI, 47 to 39; P =  .80). Additionally, protection against A(H1N1)pdm09 was observed at 63% among children who were administered the inactivated vaccine (95% CI, 45-75; P<0.001), whereas the LAIV demonstrated an efficacy of 19% against this strain (95% CI, 113 to 33; P = .55).

“Although these observational studies consistently showed lower effectiveness for the LAIV than for the inactivated vaccines, point estimates for the effectiveness of the LAIV varied widely among studies. The reasons for this are unclear,” Jackson and colleagues wrote. “The quadrivalent LAIV in the U.S., Finland and the United Kingdom were all produced by the same manufacturer at the same plant, so it is unlikely that differences in estimated vaccine effectiveness are due to variations in the vaccine product.” – by Katherine Bortz

Disclosure: Please see the study for a full list of relevant financial disclosures.