CDC: Flu shots this year reduce risk of seeing a doctor by 23%

ATLANTA — A report published in the Jan. 16 Morbidity and Mortality Weekly Report estimates that getting a flu vaccine this season reduced a person’s risk of having to go to the doctor because of flu by 23% among people of all ages.

 

Since the CDC began conducting annual flu vaccine effectiveness studies in 2004-2005, overall estimates for each season have ranged from 10% to 60% effectiveness in preventing medical visits associated with seasonal influenza illness. The MMWR report says this season’s vaccine offers reduced protection and this underscores the need for additional prevention and treatment efforts this season, including the appropriate use of influenza antiviral medications for treatment.

 

“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,” stated Joe Bresee, branch chief in the CDC’s Influenza Division. “Healthcare providers should advise patients at high risk to call promptly if they get symptoms of influenza.”

 

One factor that determines how well a flu vaccine works is the similarity between the flu viruses used in vaccine production and the flu viruses actually circulating. During seasons when vaccine viruses and circulating influenza viruses are well matched, VE between 50% and 60% has been observed. H3N2 viruses have been predominant so far this season, but about 70% of them have been different or have “drifted” from the H3N2 vaccine virus. This likely accounts for the reduced VE.

 

Flu viruses change constantly and the drifted H3N2 viruses did not appear until after the vaccine composition for the Northern Hemisphere had been chosen.

 

Another factor that influences how well the flu vaccine works is the age and health of the person being vaccinated. In general, the flu vaccine works best in young, healthy people and is less effective in people age 65 and older. This pattern is reflected in the current season early estimates for VE against H3N2 viruses. VE against H3N2 viruses was highest — 26% — for children age 6 months through 17 years. While not statistically significant, VE estimates against H3N2 viruses for other age groups were 12% for ages 18-to-49 years and 14% for people age 50 years and older.

 

The CDC recommends that people get a flu vaccine even during seasons when drifted viruses are circulating, because vaccination can still prevent some infections and can reduce severe disease that can lead to hospitalization and death. Also, the flu vaccine is designed to protect against three or four influenza viruses and some of these other viruses may circulate later in the season. Flu activity so far this season has been similar to the 2012-2013 flu season, a “moderately severe” flu season with H3N2 viruses predominating.