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Early estimates show flu vaccine 47% effective in US
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The influenza vaccine has been 47% effective overall this season in the United States, including 46% effective against the predominant circulating virus, influenza A(H1N1), according to interim estimates published in MMWR. However, the vaccine has offered “limited to no” protection in older adults, researchers said.
The vaccine’s estimated overall effectiveness compares well with past seasons, and it is higher than three of the past four. Hopes were raised recently after researchers reported that the vaccine has been 68% effective in Canada, including 72% effective against H1N1. Interim estimates from Hong Kong showed the vaccine has been 90% effective overall in children, including 92% effective against H1N1.
According to Joshua D. Doyle, MD, PhD, Epidemic Intelligence Service officer in the CDC’s Influenza Division, and colleagues, the vaccine has been 61% effective overall this season in U.S. children aged 6 months to 17 years (95% CI, 44%-73%) and 62% effective against H1N1 (95% CI, 40%-75%).
However, it has been just 24% effective overall in adults aged 50 years or older (95% CI, –15% to 51%), including only 8% effective against H1N1 (95% CI, –59% to 46%), the estimates show.
“The numbers [of infections included in the analysis] are still small but the idea that we are seeing limited to no evidence of protection for those over 50 is certainly something we want to look at very carefully,” Michael T. Osterholm, PhD, MPH, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told Infectious Diseases in Children.
The interim U.S. estimates are based on data from 3,254 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network between Nov. 23 and Feb. 2 from five study sites in Michigan, Pennsylvania, Texas, Washington and Wisconsin.
Vaccination coverage has ranged from 46% to 61% across the five study sites. Among participants with influenza, 43% received the 2018-2019 seasonal influenza vaccine compared with 57% among those who did not have influenza.
By comparison, last season’s influenza vaccine was 38% effective overall and 22% effective against influenza A(H3N2), which was the predominant circulating virus. Vaccination prevented an estimated 7.1 million illnesses, 3.7 million medical visits, 109,000 hospitalizations and 8,000 deaths last season.
Osterholm said more work has been done in the last 2 to 3 years to develop universal, game-changing influenza vaccines than was completed in the previous 20 years, but a finished product will still take a while.
“This is an exciting time to be in influenza vaccine research work,” he said. “In the meantime, the message we should emphasize is to continue to get vaccinated; even some protection is better than nothing,” he said. – by Marley Ghizzone
- References:
- Blanton L, et al. MMWR Morb Mortal Wkly Rep. 2019;doi:10.15585/mmwr.mm6806a1.
- Chiu SS, et al. Euro Surveill. 2019;doi:10.2807/1560-7917.ES.2019.24.5.1900056.
- Doyle JD, et al. MMWR Morb Mortal Wkly Rep. 2019;doi:10.15585/mmwr.mm6806a2.
- Rolfes MA, et al. Clin Infect Dis. 2019;doi:10.1093/cid/ciz075.
- Skowronski DM, et al. Euro Surveill. 2019;doi:10.2807/1560-7917.ES.2019.24.4.1900055.
Disclosures: Doyle and Osterholm report no relevant financial disclosures.