CDC, FDA discuss flu vaccine effectiveness, prepare for next year

This year's influenza vaccine has had an overall effectiveness of 19 percent, according to the Centers for Disease Control and Prevention (CDC). With an eye toward next year, the U.S. Food and Drug Administration (FDA) has recommended a trivalent vaccine that includes two strains that were not part of this year's vaccine.

Against the H3N2 virus, this year’s vaccine has been 18 percent effective during the 2014-2015 flu season, the CDC says, and against influenza B, it has been 45 percent effective. The CDC attributes the reduced effectiveness of the vaccine against H3N2 to the fact that more than two-thirds of the circulating H3N2 viruses are drifted from the H3N2 vaccine virus recommended for vaccine production. The effectiveness estimates are based on data spanning Nov. 10, 2014, to Jan. 30, 2015.

As of March 2, the CDC said, the hospitalization rate for people aged 65 or more years was 258.0 per 100,000 people, up slightly from 242.2 per 100,000 the prior week. The hospitalization rate for the ≥65-year-old age group is always highest, according to the agency, but this season’s rate is the highest recorded since this type of record-keeping began in 2005.

In February, The Lancet published a CDC co-authored observational study that compared the protection provided by the high-dose flu vaccine to the standard-dose flu vaccine. The study analyzed data from more than two million Medicare beneficiaries aged 65 or more years who had received the high-dose or standard-dose inactivated flu vaccine from community pharmacies during the 2012-2013 flu season. Results showed that 22 percent fewer probable flu cases occurred in the high-dose group than in the standard-dose group. Likewise, the high-dose vaccine was 22 percent more effective at preventing flu-related hospital admissions. This marked the first time a significant reduction in flu-related hospitalizations was shown in people who had received the high-dose vaccine versus the standard-dose flu vaccine.

Next season’s vaccine

Looking toward next year, the FDA’s Vaccines and Related Biological Products Advisory Committee met March 4 and agreed with a recommendation of the World Health Organization (WHO) as to which strains of influenza should be included in the flu vaccine for 2015-2016. In the northern hemisphere, WHO recommended that the vaccine protect against:

  • an A/California/7/2009 (H1N1)pdm09-like virus, which is the same as 2014-2015;
  • an A/Switzerland/9715293/2013 (H3N2)-like virus, which is different from 2014-2015; and
  • a B/Phuket/3073/2013-like virus, which is different from 2014-2015.

These are the same strains WHO recommended for the southern hemisphere in September. WHO also recommends that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.

Topics: Clinical