Seasonal Influenza Vaccine Only 23% Effective This Year

Lara C. Pullen, PhD

January 15, 2015

An early analysis of the 2014 to 2015 influenza season notes that two thirds of the circulating influenza A (H3N2) viruses differ from the H3N2 component of the 2014 to 2015 influenza vaccine. The 2014 to 2015 seasonal influenza vaccine is thus estimated to be only 23% effective in preventing medically attended, laboratory-confirmed influenza H3N2 infection in the overall population. Vaccine effectiveness against H3N2 viruses is estimated at just 12% for individuals aged 18 to 49 years.

Brendan Flannery, PhD, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and colleagues published their analysis in the January 16 issue of the Morbidity and Mortality Weekly Report. The investigators collected data from five centers in the United States that had outpatient medical facilities. The analysis is based on 2321 children and adults with acute respiratory illness diagnosed from November 10, 2014, to January 2, 2015.

The 2014 to 2015 influenza season began early, allowing for an early vaccine effectiveness estimate. However, the investigators point out that the early estimate is likely to be imprecise for individuals who are 18 years old and older.

Thus far, the current season has been similar to the moderately severe 2012 to 2013 season, in terms of the severity and timing of influenza activity, according to the new analysis. The results suggest that additional influenza prevention and treatment measures are needed, especially among young children, individuals who are 65 years old and older, and people who are at higher risk for serious influenza-associated complications. In particular, the authors highlight the importance of cough etiquette, social distancing, and hand washing in decreasing the spread of influenza.

The authors also suggest that antiviral treatment begin within 48 hours of the onset of symptoms. "Physicians should be aware that all hospitalized patients and all outpatients at high risk for serious complications should be treated as soon as possible with one of three available influenza antiviral medications if influenza is suspected, regardless of a patient's vaccination status and without waiting for confirmatory testing," Joe Bresee, MD, branch chief in CDC's Influenza Division, said in a press release. "Health care providers should advise patients at high risk to call promptly if they get symptoms of influenza."

The CDC began conducting annual influenza vaccine effectiveness studies in 2004 to 2005. Previous studies have found variable vaccine efficacy in seasons when the circulating virus is marked by antigenic drift.

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. 2015;64:10-15. Full text


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