H1N1 Swine Flu Still Smoldering in U.S.

More Than 300 Deaths, 2 Million New Cases in Last Month

Medically Reviewed by Laura J. Martin, MD on March 16, 2010
From the WebMD Archives

March 16, 2010 -- It's no wildfire, but H1N1 swine flu continues to smolder in the U.S.

From mid-January to mid-February, the CDC estimates there were 2 million new cases of H1N1 swine flu, causing 18,000 hospitalizations, and about 310 deaths.

From the beginning of the pandemic in April 2009 until Feb. 13, 2010, the CDC estimates there were:

  • Between 42 million and 86 million H1N1 swine flu cases. Mid-range estimate: 59 million cases.
  • Between 188,000 and 389,000 H1N1 swine flu hospitalizations. Mid-range estimate: 265,000 hospitalizations.
  • Between 8,520 and 17,620 H1N1 swine flu deaths. Mid-range estimate: 12,000 deaths.

Although 2 million new cases in a month seems like a lot, the cumulative estimates are growing much more slowly. This is consistent with reports from state and local health departments suggesting only sporadic cases popping up in most of the nation. Only in the Deep South and in Maine were regional outbreaks continuing last week.

Flu pandemics often come in waves, and there's no guarantee that the U.S. won't see a new wave of infections. The CDC is still advising people to get their H1N1 swine flu vaccine.

The latest estimates support this advice, and indicate that although flu activity is low, people continue to get infected. Serious cases continue to land people in the hospital -- and the estimated 310 deaths are 310 too many.

What's ahead? No flu expert is willing to make a firm forecast, as the disease is notorious for its unpredictability. But there's no sign of a third wave at this point, says James C. Turner, MD, president of the American College Health Association (ACHA). The ACHA conducts weekly surveillance of 197 campuses, with a total population of about 2.3 million students.

"At this point we see no definitive evidence of a third wave of influenza-like-illness disease, even on a regional basis, but we will continue to follow the surveillance data carefully," Turner says in a news release.

The CDC data show that H1N1 swine flu peaked in October and declined to below baseline levels in January. February saw further declines in activity.

"There are still uncertainties surrounding the rest of this flu season," the CDC warns. "Flu activity -- caused either by 2009 H1N1 or seasonal flu viruses -- may rise and fall, but is expected to continue for several more weeks."

In some years, flu season extends into May. And although a new spring wave of illness is possible, it seems likely that we'll continue to see sporadic cases throughout the rest of the season and perhaps in the summer as well.

One factor blunting a possible third wave of swine flu is the relative success of the vaccination program. As of mid-February, more than 86 million U.S. residents have been vaccinated against the H1N1 swine flu.

Assuming that 59 million Americans had swine flu, nearly half the nation would be immune. That's not enough to prevent a new wave -- at least half the nation remains vulnerable -- but it's a vast improvement over where we were when the U.S. epidemic peaked in October.