CDC estimates flu vaccine's impact, early coverage

Federal health officials today said their "half-time score" for flu vaccine uptake shows a slight gain compared with last season, and they said the vaccine prevented 6.6 million illnesses and 79,000 hospitalizations last season.

The latest data on flu vaccination from the US Centers for Disease Control and Prevention (CDC) comes as the nation's flu activity is starting to ramp up, mainly in southern states, and during National Influenza Vaccination Week, a broad public health effort designed to promote vaccination ahead of the season's peak, which typically occurs some time between January and March.

According to modeling estimates the CDC uses to gauge the effect of flu vaccination programs, last season's flu vaccine prevented 6.6 million illnesses, 3.2 million clinic visits, and 79,000 hospitalizations. The CDC published the full report on the finding in the latest issue of Morbidity and Mortality Weekly Report (MMWR). Researchers based their estimates on surveillance data, vaccination coverage data, and vaccine effectiveness estimates.

The CDC said the numbers are higher than similar estimate for past seasons because of the severity of the season, which was marked by the dominance of the H3N2 strain, which can cause more serious disease, and a disproportionate number of hospitalizations in older people.

'Eye-popping' numbers

At a media briefing today, CDC Director Tom Frieden, MD, called the numbers, which he said are based on a conservative model, "eye popping."

"The point is flu can cause a lot of illness, and it can be severe," he said.

According to the same report, the CDC estimated that during the 2012-13 season flu led to 31.8 million infections, 14.4 million medical visits, and 381,000 hospitalizations.  For comparison, the CDC estimates that in a typical season the disease is responsible for 200,000 hospitalizations.

CDC officials said though the flu vaccine's efficacy isn't as high as they would like, boosting coverage with the current vaccine could raise the number of prevented illnesses, clinic visits, and hospitalizations even further.

The CDC estimated that the flu vaccine effectiveness was 51% for the 2012-13 season, similar to other years. For seniors, studies have shown a dramatic drop-off in protection.

This season's vaccine uptake

So far the early-season estimate suggests that about 40% of Americans had been vaccinated through Nov 15. The CDC posted the uptake projections for the general population, pregnant women, and healthcare workers on its Web site today.

The agency bases the general population estimate on internet panel and phone survey data, and the other two estimates are based on Internet panel results.

Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, told reporters that the overall uptake is running about 3 percentage points higher than last season, and that most of the gain has been in adults under age 65 years, a group that traditionally lags behind in flu vaccine uptake.

For the other two key populations that CDC monitors, uptake is at about the same level as last year: 41% in pregnant women and 63% in healthcare workers.

Among health workers, pharmacists are in the lead thus far, with an estimated 90% uptake. Schuchat issued a friendly challenge to physicians and nurses, two other groups who typically have high coverage levels, to catch up to the pharmacists. However, as in past seasons, the CDC said it is seeing much lower coverage in medical assistants and aides (49%) and providers working in nursing homes (53%).

She said the CDC is pleased that flu vaccination is becoming a habit for many people but believes there is much room for improvement. Though a more protective flu vaccine would be ideal, "We have to do what we can with the available tools to protect ourselves and our families," Schuchat said.

CDC officials said it's not too late to be vaccinated, and they said markers showing rising levels of flu activity are a reminder that now is the time to act. "Put it on your holiday shopping list," Schuchat said.

See also:

Dec 12 CDC press release

Dec 12 MMWR report

Dec 12 CDC early season flu vaccination estimate for general population

Dec 12 CDC early flu season vaccination estimate for healthcare workers

Dec 12 CDC early season flu vaccination estimate for pregnant women

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