New Estimate on Swine Flu in U.S.

CDC Says Up to 24% of Americans Might Get Swine Flu if There Is No Vaccine

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

July 24, 2009 – A CDC flu expert estimates that without a swine flu vaccine, current trends suggest 12% to 24% of Americans might get swine flu this fall and winter.

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Over the spring and summer, H1N1 flu never went away. That's very unusual, as seasonal flu bugs don't like to spread during these warm, humid months.

In the spring, H1N1 swine flu infected 6% to 8% of people in U.S. communities that had outbreaks, says Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases.

"We think in a longer winter season, attack rates would probably reach higher levels than that, maybe more two or three times as high," Schuchat today said in a CDC teleconference. "We need to be ready for it to be challenging."

Two or three times the summer attack rate would mean 12% to 24% of people getting sick with the flu. That's a range of over one in 10 to just under one in four U.S. residents.

"We have lots of ways that we can limit the impact that it has, but it's going to take us working together," Schuchat said. "We know that our emergency rooms are often crowded in the regular year, particularly in the winter season. This particular virus might crowd the emergency department season more."

Some media have misreported Schuchat as saying that 40% of Americans would get swine flu. But Schuchat was referring to a worst-case-scenario war game in which CDC officials looked at the impact of 40% of the workforce being unable to work because they were sick or taking care of an ill family member. This is not the most likely scenario, Schuchat said.

"Worst-case scenarios we don't want to take us by surprise," Schuchat said. "A more likely scenario ... is the kind of patterns we saw in the spring in the most affected communities like New York City or Seattle, for instance."

Schuchat said the CDC is urging the medical community to help people understand that when they really need emergency care they'll need to make room for the larger-than-usual number of severe flu cases expected to occur during a wave of pandemic flu.

An effective flu vaccine would put a dent in the pandemic, if large enough numbers of people get the vaccine before the next waves of the pandemic sweep the nation. Schuchat says the CDC is telling state and local authorities to plan to start getting H1N1 swine flu vaccine in mid-October.

Swine Flu Causes Seizures in Kids

While H1N1 swine flu isn't a killer flu, a recent CDC publication warned that some kids who got the pandemic flu had seizures or other severe neurologic problems such as Reye's syndrome.

It was a scary warning, but similar neurologic complications are seen with seasonal flu, too. It's not yet known whether H1N1 swine flu is more or less likely to cause these rare but severe complications. Fortunately, all of the kids in the CDC report recovered without long-term consequences.

"We know that neurologic problems like seizures are very concerning for parents, and we want them to [know] that is one more thing to be on the lookout for in conjunction with influenza," Schuchat said. "It's another reason that we're taking this new H1N1 virus so seriously."

SOURCES: Anne Schuchat, MD, director, National Center for Immunization and Respiratory Diseases, CDC. Morbidity and Mortality Weekly Report, July 24, 2009; vol 58: pp 773-778.

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