CDC Reports 2017 Flu Vaccine Working for Less than Half of Recipients

This year’s flu vaccine is working for almost half of all recipients in what the Centers for Disease Control and Prevention (CDC) is calling a “moderate” season, according to a Morbidity and Morality Weekly Report published on the CDC website (Weekly. February 17, 2017;66(6):167-171).
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As of February 3, 2017, the CDC estimates that more than 145 million doses of influenza vaccine have been distributed throughout the United States for the 2016-17 season. While the CDC expects flu season to continue for several more weeks, so far, vaccines have been 48% effective in preventing flu-related medical visits, which is lower that the rate for last year (59%), but far higher than what was estimated in 2014-2015 (19%). Over a 10-year period, vaccine effectiveness has fluctuated, but typically falls between the low 40s and high 50s.

Interim VE estimates indicate improved protection during the 2016–17 influenza season against the predominant influenza A (H3N2) virus belonging to genetic group 3C.2a, which emerged in early 2014 and was predominant during the 2014–15 influenza season in the United States. This, authors of the report theorized, is what likely contributed to high rates of influenza-associated hospitalizations that season, especially among those aged 65 years and older.

However, while significant strides have been made to correct poor results seen in the 2014-2015 season, with a vaccine effectiveness rate of 48%, providers should expect some vaccinated persons to still become infected with influenza. As such, clinicians should maintain a high index of suspicion for influenza infection among persons with acute respiratory illness for the duration of the season, especially in children and the elderly. Antiviral medications are recommended as the primary treatment option for infected patients, regardless of their vaccination status, and the decision to use these therapies should not be delayed while waiting for laboratory confirmation.

“Annual vaccination against circulating influenza viruses remains the best strategy for preventing illness from influenza,” authors of the study concluded. However, with rates of vaccination still low in the United States, providers should work with patients to encourage immunization and bring down rates of infection.—Sean McGuire