Trivalent and quadrivalent inactivated influenza vaccine (IIV) and quadrivalent live attenuated influenza vaccine (LAIV) all gave statistically significant protection against any flu in U.S. children aged 2-17 years in 2015-2016, Katherine A. Poehling, MD, of Wake Forest University, Winston-Salem, N.C., and her associates reported in a study of more than 1,000 children.

“This study also adds to the clinical evidence suggesting that effectiveness of LAIV against influenza A(H1N1)pdm09 strains has been lower than observed with IIV since the 2009 influenza A(H1N1) pandemic,” the researchers concluded.

More than 1,000 children aged 2-17 years seeking outpatient medical care for febrile acute respiratory illness were recruited in Florida, Minnesota, North Carolina, Ohio, Oregon, Tennessee, Texas, and Wisconsin in the 2015-2016 flu season; children were required to have fever and illness onset of less than 5 days, and 84% of children had cough. A nasal swab was collected and tested for influenza and other viruses; medical records were checked for flu vaccination dates and vaccine types.

“The 2015-2016 season northern hemisphere trivalent IIV included A/California/7/2009 (H1N1)-like virus, a new A/Switzerland/9715293/2013 (H3N2)-like virus, and a new B/Phuket/3073/2013-like virus (Yamagata lineage),” the investigators noted. “Quadrivalent IIV was similar to trivalent IIV and also included B/Brisbane/60/2008-like virus (Victoria lineage). LAIV was similar to quadrivalent IIV, except that it contained A/Bolivia/559/2013.”

Of the 1,012 children enrolled, 59% were unvaccinated, 10% were given LAIV, 10% received trivalent IIV, 20% were given quadrivalent IIV, and 1% received IIV of “unknown valence.”

Vaccine efficacy against any influenza was 46% for LAIV and 65% for IIV, compared with no vaccination. But only IIV gave “significant protection against influenza A(H1N1)pdm09 strains in the total study population,” Dr. Poehling and her associates said. Vaccine efficacy against influenza A(H1N1)pdm09 strains was 50% for LAIV and 71% for IIV.

Read more in Clinical Infectious Diseases (2017 Oct 4. doi: 10.1093/cid/cix869 ).