Vaccination Prevented Millions of Flu Cases During 2012-2013 Season

A CDC report finds that vaccination had a particularly profound effect on high-risk populations, but that higher rates of coverage would have prevented millions more cases of flu.

Flu shots prevented an estimated 6.6 million cases of flu-related sickness during the 2012-2013 flu season, according to a recently released report from the Centers for Disease Control and Prevention. Nonetheless, as of November 2013, just 40% of Americans aged 6 months and older had reported getting the shot so far this season.

The report, which was published in the December 13, 2013, issue of Morbidity and Mortality Weekly Report, found that from October 2012 to May 2013, vaccination also led to 3.2 million fewer medically attended illnesses and 79,260 fewer flu-related hospitalizations. These numbers translate to an overall 17.3% reduction in the number of adverse health outcomes associated with the flu. The estimated number of cases and hospitalizations prevented by vaccination during the 2013-2013 flu season are the highest reported for all seasons studied by the CDC, which may be due to the fact that it was a particularly severe season.

The report also notes that vaccination had a profound effect on high-risk populations. Children aged 6 months to 4 years and adults aged 65 and older accounted for 69% of avoided hospitalizations, 39% of avoided medically attended cases, and 29% of avoided illnesses. Vaccine effectiveness was estimated to be lowest among those aged 65 and older. However, the high rate of vaccine coverage combined with the high risk for severe outcomes in this age group led to significant reductions in hospitalizations. In fact, 56% of prevented hospitalizations during the season were in patients aged 65 and older.

Although vaccination prevented an unprecedented number of cases and hospitalizations in 2012-2013, the report notes that significantly more cases could have been avoided if more people had been vaccinated. If coverage had reached the Healthy People 2020 target of 70%, an additional 4.4 million cases, 1.8 million medically attended cases, and 30,000 hospitalizations could have been prevented.

Despite efforts to increase coverage with the influenza vaccine, vaccination rates for the 2013-2014 season so far are similar to those seen in previous seasons. The CDC estimates that, as of early November 2013, only 40% of Americans aged 6 months and older had received the flu shot, which is similar to the coverage rate at the same point last season.

“Strategies known to improve coverage should be encouraged,” an editorial note included in the report reads. “Those include ensuring that all those who visit a provider during the influenza season receive a vaccination recommendation and offer from their provider and using immunization information systems.”

Since the burden of this year’s flu season cannot be predicted, the CDC suggests that vaccination should continue to be offered as long as the virus continues to spread.