H1N1 flu virusiStockphoto

While Boston has declared a public health emergency in response to its flu outbreak, a school district in Oklahoma canceled classes, and some hospitals are setting up overflow tents and limiting visitors, some flu experts say that the perception of the severity of this year's strain of the flu -- called H3N2 -- may be worse than reality.

The Centers for Disease Control and Prevention said today that 47 states reported widespread geographic influenza activity. That includes high levels in 24 states and moderate levels in 16 states. Some areas saw a decline this week.

That makes this a "moderately severe" year for flu, experts said, but, because 2010-11 and 2011-12 were relatively mild years, this season seems much worse.

"We haven't had a severe year since 2003-04, and that was the year the vaccine did not match very well," said Thomas Haupt, Influenza Surveillance Coordinator for the Wisconsin Division of Public Health. "I don't think it will get to that proportion."

This year's flu vaccine is 62 percent effective, the CDC reported today, meaning that those who got the flu shot have a 62 percent less likelihood of going to the doctor for flu than those who didn't get it. Of the remaining 38 percent, the flu shot can alleviate some of the symptoms, resulting in a much milder illness.

"What's catching people off-guard is that after being lulled by two years of no significant influenza, we're being reminded of how devastating it can be in its natural state," said Dr. Jonathan Temte, chair of the U.S. Advisory Committee on Immunization Practices and a professor at the University of Wisconsin School of Medicine and Public Health. "This is pretty normal."

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In 2009-2010, the virus called H1N1 reached pandemic proportions. This year's strain is quite different, in a number of ways. First, it's a known quantity. H1N1 was a novel virus, and no one had any resistance to it; the initial vaccine in 2009 wasn't effective against it. H1N1 hit young people; this virus is hitting the older population. But in general, H3 viruses are generally harsher than H1 viruses, Temte said.

"H3N2 is in general associated with more morbidity and mortality -- more sickness and death -- than H1N1 and Influenza B," Temte said. "H1N1 was incredibly widespread, but it was also incredibly wimpy. The only reason we saw so much mischief from it was that no on had immunity against it. On average, the H3N2 is the more nasty type."

There have been 20 pediatric deaths from flu this year, today's CDC report showed. While the CDC doesn't track adult deaths from influenza, approximately 24,000 die annually.

There are some indications that the flu season has already peaked. The season started a bit earlier than usual, so the declines seen in some southeastern states could indicate the downside of a peak. Flu season usually averages 12 consecutive weeks, according to the CDC.

"My anticipation is that in two or three weeks we'll be on the backside of this," Temte said.

Trends are hard to predict, however, and data over the holiday week usually isn't representative of an average week, which can skew the overall results. Next week's data may show a more obvious downward slope.

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"The only thing predictable about the flu is that it's unpredictable," said CDC director Dr. Tom Frieden on a media conference call. "It ebbs and flows during flu season."

It takes a while for the season to peter out, however; new cases still pop up 10-12 weeks after the peak. That means there's still plenty of potential benefits from the vaccine, experts said. The CDC recommended calling your provider ahead of time, however: the vaccine is available, but some supplies at some clinics have run out.