Influenza vaccines reduced the risk of influenza illness overall during the 2015-2016 season, according to data published in the New England Journal of Medicine. However, the live attenuated vaccine was ineffective among children between 2 and 17 years of age.
Michael L Jackson, PhD, from the Group Health Research Institute in Seattle, and colleagues reported the estimates from the Influenza Vaccine Effectiveness Network from the 2015-2016 season, including comparisons between the trivalent and quadrivalent inactivated vaccines and the quadrivalent live attenuated vaccine.
Investigators enrolled 6,879 patients 6 months or older who presented with acute respiratory illness at ambulatory care clinics. They estimated vaccine effectiveness using a test-negative design. The researchers found that 19% of participants tested positive for the influenza virus—11% of participants tested positive for the A(H1N1)pdm09 strain, and 7% tested positive for influenza B.
The effectiveness of the influenza vaccine against any influenza illness was 48%, and among children between 2 and 17 years of age, the inactivated influenza vaccine was 60% effective. However, the effectiveness of the live attenuated vaccine in children in this age group was 5%. In addition, vaccine effectiveness against the A(H1N1)pdm09 strain in children was 63% for the inactivated vaccine, compared with -19% for the live attenuated vaccine.
“Potential explanations for the live attenuated vaccine having lower effectiveness than the inactivated vaccine in this group remain unclear but may include poor replicative fitness of its A(H1N1)pdm09 strains or vaccine-virus interference,” the researchers note. “Although the quadrivalent live attenuated vaccine remains licensed in the United States, the ACIP did not recommend this vaccine for the 2016–2017 influenza season.”
Jackson ML, Chung JR, Jackson LA, et al. Influenza vaccine effectiveness in the United States during the 2015-2016 season. N Engl J Med. 2017;377:534-543.