The US Food and Drug Administration's (FDA's) Vaccines and Related Biological Products Advisory Committee has chosen the influenza vaccine strains for the 2018-2019 season in the Northern Hemisphere, which begins in the fall of 2018.
On February 22, the World Health Organization made its recommendations as to which influenza strains to include in vaccines for the coming influenza season. The committee voted on those recommendations today.
Overall vaccine effectiveness against influenza A(H3N2) — the predominant strain of influenza this season — has been 25% as of February 15.
FDA Commissioner Scott Gottlieb, MD, said in a February 26 news release that he believes the influenza A(H3N2) virus strain selected for this season's vaccine was appropriate and that experts are working to determine why the vaccine was less effective than expected.
"[S]cientists at FDA are collaborating with colleagues at Centers for Medicare & Medicaid Services to use a large database that includes details of the flu vaccines administered to four million individuals along with whether they were hospitalized for influenza or treated with antiviral medications for influenzalike illness," Gottlieb explained.
"This work, which is still underway, will try to better understand why overall effectiveness with both the cell-based and egg-based vaccines was less than optimal. We're also looking at the difference in effectiveness in people 65 years and older who were vaccinated with high-dose influenza vaccine and adjuvanted influenza vaccine to see if effectiveness was better than in those vaccinated with standard-dose vaccines."
Vaccine Strains
For the trivalent vaccine, the committee voted unanimously (12 yes, 0 no) to include an A/Michigan/45/2015 (H1N1)pdm09-like virus. The panel voted unanimously to include an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus, which is a change from the 2017-2018 vaccine.
The group voted by a large margin (11 yes, 1 abstain) to include a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage), which is a change from this season's vaccine.
The committee also voted unanimously to include a B/Phuket/3073/2013-like virus (B/Yamagata/16/88 lineage) as the second influenza B strain in the quadrivalent vaccine.
Vaccine Effectiveness Lower Than Expected
Interim results for this season show that vaccination lowered the number of cases of medically attended influenza illness by 36%. Vaccine effectiveness against influenza A(H3N2) was 25% for all ages and 51% for children aged 6 months to 8 years. There were no statistically significant estimates of vaccine effectiveness against influenza A(H3N2) for other age groups. The vaccine was 67% effective against A(H1N1)pdm09 and 42% effective against influenza B (mostly B/Yamagata, not in inactivated influenza vaccine, trivalent).
"In terms of last year's vaccine...even though we've had a bad flu year, the strains that were selected...were really good selections. They were as good as one could guess and make at the time. I don't think we could've done any better, and I'm encouraged by the fact that particularly [in children aged 6 months] to 8 years old it's almost 60% effective," said temporary voting member Jack Bennink, PhD, senior managing epidemiologist, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland.
Influenzalike Illness Activity Remains High Across the United States
Influenza A(H3N2) viruses were predominant during the 2017-2018 season; however, influenza B activity is rising. Influenzalike illness (ILI) activity fell from 7.4% during week 6 of 2018 to 6.4% during week 7. ILI activity continues to be higher than peak activity seen during many past seasons and is the highest observed since 2009. Hospitalization rates and mortality for adults could be as high or higher than those seen during the 2014-2015 season.
Most of the circulating influenza strains are like those in the 2017-2018 vaccine. The majority of influenza B infections were caused by B/Yamagata lineage viruses. The B/Victoria lineage viruses are the only ones showing clear antigenic drift but represent less than 1% of circulating viruses.
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