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
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
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
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
"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.