Influenza Vaccine Efficacy Better Than Expected, But More Work to Do

Published Online: Friday, February 16th, 2018
The influenza vaccine's efficacy has been somewhat better than previously predicted, but there's more work to do to improve protection, according to a statement from FDA Commissioner Scott Gottlieb, MD. The CDC released interim estimates of the 2017-2018 seasonal influenza vaccine effectiveness, reporting an overall adjusted vaccine effectiveness of 36% so far. 

"Although the initial report of 36% overall efficacy for this year’s vaccine in the United States that has been reported by our colleagues at the US CDC is better than some might have predicted, there is still clearly significant room for improvement," said Dr. Gottlieb.  "The FDA is committed to working together with the scientific and medical communities to better protect the public against the flu and apply lessons learned to next season’s flu vaccines."1

Although the overall efficacy of the vaccine is 36%, the vaccine is still only estimated to be 25% effective against influenza A (H3N2) virus, according to the CDC.2 The interim estimate indicates that vaccination provided some protection, in contrast with recently reported nonsignificant estimates of 17% efficacy in Canada and 10% in Australia. Efficacy against influenza A in the 2016-2017 season was 32%.

This year much of the illness has been caused by one strain of influenza A called H3N2, with another strain of influenza A called H1N1 and strains of influenza B contributing to lesser extents, Gottlieb said. Beyond the predominant circulating influenza strain, other aspects have contributed to making this a particularly difficult flu season. Chief among them is the fact that this season has managed to hit most of the country at the same time, while a typical flu season tends to hit parts of the country at different times. This massive influx of ill individuals has not helped the already-strapped stores of intravenous bags—which were diminished after supply plants on Puerto Rico were damaged in Hurricane Maria—and stores of antiviral medications.

FDA officials are collaborating with the CDC, the National Institutes of Health (NIH), and other federal partners to address the full spectrum of measures that need to be taken to ensure optimal protection against the flu. These measures include working to select the most appropriate flu strains for inclusion in seasonal influenza vaccines, providing seed viruses and quality control reagents to manufacturers, and ensuring the overall quality of the manufacturing proces, according to the statement. 

In a related press briefing, Department of Health and Human Services (HHS) secretary Alex Azar, stressed that there is time for every American over the age of 6 months to get a flu vaccine and compared not getting a flu shot to riding in a car without a seatbelt.

According to an update from the CDC's Morbidity and Mortality Weekly Report, 63 influenza-associated pediatric deaths have been cofirmed as of February 3, 2018.
Among those who were eligible for the vaccine and for whom vaccination status was unknown, only 14 had received any influenza vaccine this season before the onset of illness. 

The overall hospitalization rate for influenza for the week ending February 3, 2018, exceeded the rate for the same week in the 2014-2015 season, which was also an influenza A virus-predominant season categorized as high severity. 

In influenza seasons with increased severity, antiviral medications are an increasingly crucial adjunct to vaccination. The CDC continues to recommend influenza vaccination, indicating that there may still be several more weeks of elevated activity. 

This article contains reporting from Contagion. 

Reference

1. Statement from FDA Commissioner Scott Gottlieb, M.D. on the efficacy of the 2017-2018 influenza vaccine [news statement] FDA website. Feb. 15, 2018. Accessed at: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm597077.htm

2. Flannery B, Chung JR, Belongia EA, et al. Interim Estiamtes 2017-18 Seasonal Influenza Vaccine Effectiveness - United States, February 2018. MMWR. 2018. 67(6);180-185. https://www.cdc.gov/mmwr/volumes/67/wr/mm6706a2.htm 

3. Budd AP, Wentworth DE, Blanton L, et al. Update: Influenza activity - United States, October 1, 2018-February 3, 2018. MMWR. 2018. 67(6);169-279. https://www.cdc.gov/mmwr/volumes/67/wr/mm6706a1.htm?s_cid=mm6706a1_w 


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