Flu Vaccine More Effective Than Last Year's, CDC Says

February 20, 2014

The seasonal influenza vaccine for 2013-2014 so far is outperforming its predecessor from last season in protecting Americans from the flu bug, the Centers for Disease Control and Prevention (CDC) announced today.

That news is especially important, the CDC said, for young and middle-aged adults who post the lowest influenza vaccination rates of all Americans and account for most flu-related hospitalizations this season.

The seasonal vaccine is reducing a vaccinated person's risk of needing to see a clinician about influenza illness by 61% compared with an effectiveness rate of 51% in the 2012-2013 flu season, according to an article published in the February 21 issue of the agency's Morbidity and Mortality Weekly Report (MMWR). In some years, the effectiveness rate has dipped below 40%.

Furthermore, the current influenza vaccine offers "solid protection" across all age groups, said Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, in a news briefing today.

Vaccine effectiveness is 67% for children aged 6 months through 17 years, 60% for adults aged 18 through 64 years, and 52% for adults aged 65 years or older.

In 2012-2013, the vaccine was only 32% effective among seniors.

Another feather in the hat of this year's vaccine is that it is equally effective (62%) against the pandemic A(H1N1) virus, the predominant virus in circulation now.

The effectiveness data reported in MMWR are based on a study of 2319 adults and children receiving outpatient care for an acute respiratory illness between December 2, 2013, and January 23, 2014. Because the flu season is far from over, the effectiveness rates cited are interim estimates. The CDC will publish estimates for the entire flu season later this year.

Don't Wait for Lab Confirmation to Treat Suspected Flu

Since its debut in 2009, the pandemic A(H1N1) virus has been circulating every year, prompting its inclusion in seasonal vaccines. However, 2013-2014 is the first influenza season since 2009-2010 in which the pandemic virus is predominant, accounting for 98% of the viruses detected in the 2319 patients studied by the CDC, according to the MMWR article.

And as it did in 2009-2010, the pandemic virus is takings it toll especially among young and middle-aged adults. Americans aged 18 to 64 years represent 61% of all influenza-related hospitalizations, close to the 56% rate in 2009-2010, according to a second article in the latest issue of MMWR. In the 3 intervening influenza seasons, this demographic accounted for only 35% of influenza-related hospitalizations.

Likewise, 62% of influenza deaths have occurred among adults age 25 to 64 years, about the same rate as in 2009-2010.

"Flu hospitalizations and deaths are a painful reminder that the flu can be a danger for everyone," said CDC Director Tom Frieden, MD, MPH, in today's news briefing. "The good news is that this year's flu vaccine…protects people across all age groups."

Dr. Frieden advised clinicians that if a patient presents with flu symptoms, they should "treat for flu promptly" with antiviral medicines rather than wait for lab tests to confirm the diagnosis. Quick treatment is especially important, he said, for patients with underlying conditions such as asthma, lung disease, diabetes, and obesity that put them at a higher risk for complications.

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