Study: Influenza Vaccine Effectiveness Higher in Children With Prior-Season Vaccination

A recent study of children aged 2 to 17 years found that live attenuated influenza vaccine (LAIV) effectiveness was higher in those vaccinated in both the enrollment season and the prior season, compared with those children who were vaccinated only in the enrollment season.

The study found no association between prior season immunization and reduced influenza vaccine effectiveness (VE).¹

The findings support CDC recommendations for annual influenza vaccination among children, according to researchers.^1,2

The 2017-2018 flu season was severe, with 172 pediatric flu deaths reported across the country by mid-June 2018, according to the CDC.

About 80% of those deaths occurred in children that had not received the influenza vaccine for the 2017-2018 season.³

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In a report published by the Journal of the American Medical Association open network, the researchers indicated that some previous studies have reported negative effects of prior-season vaccination.

However, the effects of prior-season flu vaccination on VE in children are not well understood, they wrote.¹

From 2013-2014 through 2015-2016, an observational study was performed using the test-negative design to estimate the seasonal effectiveness of quadrivalent LAIV in children. Through an analysis of data, the authors assessed possible association between prior-season vaccination and VE. Although prior-season vaccination was not associated with either inactivated or live attenuated vaccine effectiveness against influenza A (H1N1)pdm09, the authors found evidence of residual protection with prior-season vaccination against influenza B.¹

Overall, influenza VE varied by virus subtype and type, as well as vaccine type, but prior-season vaccination was not associated with reduced VE. Of 3369 children (52% male) included in the data analysis, 23% had a positive test result for influenza, and 50% were vaccinated in the enrollment season.¹

Among LAIV recipients, VE against influenza A(H3N2) was higher among children vaccinated in both the enrollment and 1 prior season (50.3% [95% CI, 17.0% to 70.2%]) than among those without 1 prior season vaccination (−82.4% [95% CI, −267.5% to 9.5%], interaction P < .001). The effectiveness of LAIV against influenza A(H1N1)pdm09 was not associated with prior season vaccination among those with prior season vaccination (47.5% [95% CI, 11.4% to 68.9%]) and among those without prior season vaccination (7.8% [95% CI, −101.9% to 57.9%]) (interaction P = .37).¹

Prior season vaccination was not associated with effectiveness of IIV against influenza A(H3N2) (38.7% [95% CI, 6.8% to 59.6%] among those with prior-season vaccination and 23.2% [95% CI, −38.3% to 57.4%] among those without prior-season vaccination, interaction P = .16) or with effectiveness of IIV against influenza A[H1N1]pdm09 (72.4% [95% CI, 56.0% to 82.7%] among those with prior season vaccination and 67.5% [95% CI, 32.1% to 84.4%] among those without prior season vaccination, interaction P = .93).¹

In addition, residual protection from prior season vaccination only (no vaccination in the enrollment season) was observed for influenza B (LAIV: 60.0% [95% CI, 36.8% to 74.7%]; IIV: 60.0% [36.9% to 74.6%]). Similar results were observed in analyses that included repeated vaccination in 2 and 3 prior seasons.¹

The CDC recommends an annual flu vaccine for everyone aged 6 months and older. For the 2018-2019 flu season, the LAIV nasal spray is again a recommended option, offering an alternative to flu vaccination shot.²

The nasal spray is approved for use in nonpregnant individuals aged 2 to 49 years.

There is a precaution against the use of LAIV for people with certain underlying medical conditions, according to the CDC.²

Although the CDC recommends getting vaccinated against influenza by the end of October, agency officials have said the flu vaccine can still be beneficial later in the season and should still be received, even past January. Individuals should get their flu vaccinations prior to these viruses spreading in their communities. Following vaccination, it takes about 2 weeks for antibodies that protect against flu to develop in the body.²

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References

• McLean H, Caspard H, Griffin M, et al. Association of prior vaccination with influenza vaccine effectiveness in children receiving live attenuated or inactivated vaccine. JAMA Network Open. 2018;1(6):e183742. doi:10.1001/jamanetworkopen.2018.3742
• CDC. Frequently asked flu questions 2018-2019 influenza season. cdc.gov/flu/about/season/flu-season-2018-2019.htm. Updated November 5, 2018. Accessed Nov. 5, 2018.
• CDC. CDC reported flu deaths in children exceeds seasonal high. cdc.gov/flu/spotlights/reported-flu-children-deaths.htm. Updated June 8, 2018. Accessed November 5, 2018.