Flu Vaccine Kept 79,000 Out of Hospital Last Year, CDC Says

December 12, 2013

The seasonal influenza vaccine for 2012-2013 kept an estimated 79,000 people out of the hospital and prevented 6.6 million influenza illnesses, including 3.2 million medically attended ones, but these good numbers could have been far greater if more people had been immunized, the Centers for Disease Control and Prevention (CDC) announced today.

"It's definitely worth getting the flu shot," CDC Director Thomas Frieden, MD, MPH, said at a news briefing today.

According to an article by the CDC, published in the December 13 issue of the Morbidity and Mortality Weekly Report, only 44.7% of Americans received the seasonal influenza vaccine during 2012-2013. The agency calculated that if the coverage rate had hit the 70% target set by the Healthy People 2020 initiative, an additional 4.4 million influenza illnesses and 30,000 hospitalizations might have been avoided.

As of early November, the overall vaccination rate for the new 2013-2014 season was 40%, which is 3 percentage points higher than in November 2012.

Vaccination rates during the previous influenza season varied widely by age group. Children aged 6 months to 4 years led the way, at 69.3%, followed by adults aged 65 years and older, at 66%. The lowest rate — 35.8% — belonged to adults aged 20 to 64 years. The age bracket of 5 to 19 years had a vaccination rate of 48.5%.

The high coverage among seniors compensated for a vaccine effectiveness rate of only 32.0% in this age bracket, according to the authors. Seniors, who historically account for most influenza-related inpatient care, benefited from vaccination more than anyone else in terms of staying out of the hospital. Almost 6 in 10 averted hospitalizations were in this age group. For seniors to gain more protection from influenza, the United States will need to not only boost immunization rates but also improve vaccine efficacy.

In the news briefing today, Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, noted that 1 vaccine (Fluzone HD, Sanofi Pasteur) on the market, designed for seniors, packs a higher dose to compensate for a weaker immune response in this population. "The data so far suggests a higher immune response [with Fluzone HD] compared to the regular dose," Dr. Schuchat said. However, she stopped short of urging that all seniors automatically receive it.

"We recommend that the best flu vaccine to get is the one your doctor or pharmacist has," said Dr. Schuchat. "There's exciting new information about the high dose vaccine, but we're not recommending it yet as preferential over the others."

For all age groups, the 2012-2013 seasonal influenza vaccine had an estimated effectiveness rate of 51.0%, which the agency called similar to estimates for previous influenza seasons.

Current Influenza Season Off to Slow Start

For all the benefit gained from influenza vaccine, last year's influenza season was more severe than most, according to the CDC. It accounted for an estimated 381,474 hospitalizations and almost 32 million cases of influenza illness, with 45% resulting in medical care.

Dr. Schuchat noted that the influenza virus "hit early and hit hard" at the beginning of the 2012-2013 season, in contrast to the usual pattern of influenza peaking in January through March.

"This year, [influenza] hasn't taken off widely yet," she said. "It's too early to tell you what this season will be like."

So far, 3 children have died from influenza during the current season compared with 169 during the entire 2012-2013 season. Dr. Schuchat noted that vast majority of pediatric deaths occur among unvaccinated children.

"The flu vaccine isn't perfect," she said. "It won't prevent every single illness and death. But for parents, [vaccination] is one thing you can do to protect yourselves and your children. We want every child vaccinated."

Dr. Schuchat singled out other groups for greater vaccination coverage.

"We're tracking pregnant women," she said. "They can have very severe complications from influenza, and their babies can be very sick and even die. So it's very important for pregnant women to get vaccinated. Comparing this year with last year, we're just about at the same point — about 41% of pregnant women have been vaccinated as of mid-November. We have more work to do."

Dr. Schuchat also encouraged healthcare workers to improve their vaccination coverage, which is running at 63%, roughly the same as a year ago. Getting a shot is critically important for personnel in long-term care facilities serving the elderly.

"Sadly, that is the population of healthcare workers lagging behind [in vaccination]," Dr. Schuchat said.

Morb Mortal Wkly Rep. 2013;62:997-1000. Full text

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