COMMENTARY

Why No LAIV Again This Year?

William T. Basco, Jr, MD, MS

Disclosures

October 11, 2017

Which Flu Vaccines Are Effective in Children?

Most pediatric providers remember that data obtained from national surveillance networks for the 2013-2014 influenza season suggested that the live attenuated influenza vaccine (LAIV) was not effective against the influenza A virus circulating that year. A different A(H1N1) strain was used in the LAIV for the 2015-2016 influenza season. A recent report by Jackson and colleagues[1] details the effectiveness of both injectable and LAIV influenza vaccines during the last influenza season, on the basis of data from a national surveillance system meant to provide a representative sample of the United States.

The children in this study were at least 6 months old and presented for care with acute respiratory illnesses during the 2015-2016 influenza season. The study excluded children who were already taking antiviral agents.

Both trivalent and quadrivalent vaccines were available in this influenza season. Both varieties contain two influenza A strains, and the quadrivalent vaccine also included two influenza B strains. The children were tested for influenza by nasal swab at presentation.

The effectiveness of the vaccines was estimated by comparing the odds of testing positive for influenza among children who had received a vaccination with the odds of testing positive among the unvaccinated study population. The researchers estimated effectiveness of the vaccines against "any influenza illness" as well as strain-specific effectiveness.

This study enrolled 6879 children, 19% of whom were positive for influenza at enrollment. An influenza A virus (predominantly H1N1) was isolated from 64% of the children with flu. B strains were isolated from 34% of the children with flu, and less than 1% had coinfection with an A and a B strain.

After adjustment for confounding variables, the vaccine effectiveness for any influenza virus was 48% (95% confidence interval [CI], 41%-55%). The effectiveness rates by virus subtype were fairly small, ranging from 43% to 57%.

Of note, effectiveness was noted only for the inactivated vaccine and not for the LAIV, which had an estimated vaccine effectiveness of only 5% (95% CI, 47%-39%). The effectiveness for the inactivated vaccine was 60%. Overall, little difference was found between the estimated effectiveness of the quadrivalent inactivated vaccine and the trivalent inactivated vaccine.

The investigators concluded that influenza vaccines were effective in 2015-2016, but the LAIV was not effective.

Viewpoint

These are the data that prompted last season's decision by the Advisory Committee on Immunization Practices to not recommend the LAIV for the 2016-2017 influenza season. The A(H1N1) in the 2016-2017 vaccine was the same as that used in the 2015-2016 vaccine.

Of note, the fact that the LAIV is not recommended for the current influenza season (2017-2018) is considered an "interim recommendation" because data from 2016-2017 influenza season are still being evaluated.[2] The A(H1N1) strain to be used in the 2017-2018 season is different from that used in the two previous seasons, but we don't yet know whether it will work in LAIV form. Stay tuned!

See the American Academy of Pediatrics Recommendations for Prevention and Control of Influenza in Children, 2017-2018 for more information on recommendations for the upcoming influenza season.

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