June 3, 2010— -- Even as an emergency committee that advises the World Health Organization announced today that swine flu is still a pandemic, medical authorities in the United States say the H1N1 virus is past its peak.
World Health Organization director Margaret Chan said the current pandemic alert level will remain at the highest possible -- phase 6. Chan said the WHO may revisit the decision in July.
Between 43 million and 89 million people caught H1N1 in the year since U.S. officials discovered the virus in April 2009 and between 8,870 and 18,300 people died, according to estimates by the national Centers for Disease Control and Prevention.
But the CDC stopped reporting H1N1 flu infections by late May, stating on its Web site that "only a small number of influenza viruses are being reported, most of which are 2009 H1N1."
"The 'pandemic' refers to the large numbers of influenza epidemics occurring coincident with the spread of the new strain," said Dr. Donald Henderson, the resident scholar at the Center for Biosecurity at the University of Pittsburgh Medical Center.
"That occurred and basically burned itself out weeks ago. But the strain and some cases continue to occur and will continue to occur until a new pandemic strain emerges."
The WHO reports that the Caribbean, Central America and Cuba "continue to experience active circulation of pandemic influenza."
But the widespread infections may actually be reason to finally relax about H1N1. As the flu spreads through a community, those infected will build up immunity. Then, if enough people in one area are immune, the virus will not have a chance to spread to those in the community who aren't immune.
"The H1N1 pandemic was so widespread for a fairly extended period of time, there really hardly isn't an area of the globe it didn't affect," said Dr. Pascal Imperato, dean and distinguished service professor at the SUNY Downstate Medical Center School of Public Health in Brooklyn, New York.
Herd Immunity May Protect Against Future Outbreaks
"There's pretty much a solid heard immunity against this particular virus. It would be very difficult to impossible to cause another pandemic," said Imperato.
The new strain of H1N1 flu -- which was genetically linked to a strand of flu affecting swine -- popped up at the end of spring in 2009, prompting the WHO and CDC to race to develop a vaccine before flu season.
But once the vaccine was manufactured and available, states found they had an ample supply and a dwindling demand.
CDC officials announced on April 1 this year that at least 71 million vaccines were left unused, which may be thrown away, donated or reused to make more vaccines later.
"It was very difficult to get people to come out [for the H1N1 vaccine] once they had herd immunity," said Imperato. "Especially those parts of the country that had been affected in the first wave, back in the spring -- like New York City."
Although the H1N1 strain was unusual because it appeared in spring, the virus may actually fall into the normal pattern for flu.
"What people forget is that a new pandemic occurs, sweeps across the world in epidemic form, subsides during the off-season but continues to spread and it becomes what is called 'seasonal influenza,'" said Henderson.
"Such was the story after [the flu of] 1918, 1957, and 1968. This pandemic is all but a carbon copy of 1957 but not terribly unlike 1968," he said.
Henderson, who directed eradication of small pox under the World Health Organization, said people should be open about the "threat" of H1N1.
"What our colleagues must keep in mind that there is a need to be open and frank with the public at all times," he said. "Some would like to have the threat of 'continuing pandemic' on the label as an encouragement for more people to get vaccinated. Not a good idea."
How Does the Public React to Pandemic Warnings
Looking forward, most U.S. doctors agree that the H1N1 has fizzled out. But some doctors feel that the public underestimated the potential threat of H1N1 virus last year.
"We should be careful not to blame the government for over exaggeration of risk. They did exactly what they were supposed to do and did it reasonably well," said Dr. Peter Katona, of the David Geffen School of Medicine at the University of California Los Angeles.
"There was a lot to learn. This will happen again and we will need to be prepared - maybe even more prepared - the next time," said Katona, who previously worked for the CDC.
Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University, has already begun to hear questions about how H1N1 will affect next year's seasonal flu shot.
"Patients will be asking 'if I got the H1N1 last year, do I need to get the vaccine this year?' or 'Gee, I thought I was sick with H1N1 last year, should I get the vaccine this year?'" said Schaffner. "The answer is yes."
However this year, the seasonal flu vaccine will include protection against H1N1 and, for the first time, the CDC's Advisory Committee on Immunization Practices will recommend everyone over age 6 months be vaccinated for the flu.
Previously the committee only recommended children age 6 months to 18 years, and people in contact with others with a "high risk" group receive the vaccine.
"We're not still in a pandemic mode," said Schaffner, who added it was "luck" that many of the elderly had built up immunity to a virus similar to H1N1 in the 1950s.
"Some of the protection we got from our infection back then carried over this past year," said Schaffner. "If we had not had that kind of protection, I can assure you that it would have been a very grim flu season."
The Associated Press contributed to this story