CDC's early estimate finds this year's flu vaccine 59% effective

A preliminary estimate puts the overall effectiveness of this year's influenza vaccine at 59%, federal officials announced today, which is about triple the number last year, when the vaccine matched up poorly with the dominant circulating flu strain.

The Centers for Disease Control and Prevention (CDC) announced the estimate in a press release as it was presented at a meeting of the agency's Advisory Committee for Immunization Practices (ACIP).

"This means that getting a flu vaccine this season reduced the risk of having to go to the doctor because of flu by nearly 60 percent," Joseph Bresee, MD, chief of the CDC's Epidemiology and Prevention Branch, said in the release. "It's good news and underscores the importance and the benefit of both annual and ongoing vaccination efforts this season."

The agency noted that 59% is similar to past seasons when the vaccine was well-matched to circulating strains. In contrast, overall vaccine effectiveness (VE) in the 2014-15 season was estimated at only 19%, mainly because the vaccine's H3N2 component worked poorly against most circulating H3N2 viruses, offering only 18% protection against that strain. H3N2 was the heavily predominant strain last year.

The CDC said it had enough data to estimate VE against some of the specific flu strains this season:

  • 51% against H1N1 viruses, which are responsible for most flu cases this season
  • 76% against all influenza B viruses
  • 79% against the B/Yamagata lineage of B viruses

Not enough data are available yet to estimate VE by age-group or against H3N2 or B/Victoria lineage viruses, the agency said. The estimates are based on data gathered by the US Flu VE Network from Nov 2, 2015, through Feb 12, and the numbers could change as the season continues, officials noted.

Flu activity has now been elevated for 5 straight weeks, since mid-January, the CDC said. Flu seasons over the past 13 years have averaged 13 weeks in length.

In other ACIP news, the committee renewed the universal recommendation for flu vaccination, in place since 2010, the agency said. Also, the panel amended flu vaccine recommendations for egg-allergic patients so that they may now receive the live attenuated (nasal spray) flu vaccine.

See also:

Feb 24 CDC press release

Apr 28 CIDRAP News item on 2014-15 season

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