*Scientists see no overreaction
*US and world health experts learned from history
*H1N1 virus could pose threat for months
By Maggie Fox, Health and Science Editor
WASHINGTON, May 4 (Reuters) - With Mexico saying the worst may be over and the new H1N1 virus starting to look more like a seasonal flu strain in the United States and elsewhere, critics are going to start asking if public health officials overreacted to the outbreak.
Since the new swine flu virus was first identified two weeks ago in two children in Texas and California, the World Health Organization pushed its pandemic alert level from a three to a five, meaning a pandemic is imminent.
Mexico closed schools, stopped public events and took a big hit to tourism. The U.S. government mobilized 25 percent of its stockpile of antiviral drugs and started work on a vaccine against the new strain.
But the death toll is being rolled back as Mexican officials realize it will be impossible to know if long-buried or cremated victims died of H1N1 swine flu. And while the infection is spreading rapidly across the United States, it appears to be no worse than seasonal flu.
Scientists who study flu say the coordinated, global response was appropriate.
"If it doesn’t become more virulent, first of all, many people will heave a great sigh of relief," said Dr. Scott Lillibridge, who helped set up the Center for Disease Control and Prevention’s Bioterrorism Preparedness and Response Program and who is now at the University of Texas Health Sciences Center in Houston.
But Lillibridge echoes what the WHO and CDC have been saying: viruses mutate and change all the time and it is too early to say how bad this virus really is.
"We are only a few days into a major international mobilization for an outbreak that could continue months into the future," Lillibridge said in a telephone interview.
The U.S. government has been preparing for this scenario for years.
One of the messages that has come up repeatedly is that the 1918 pandemic, cited as the worst-case scenario because it killed upwards of 40 million people, started with a mild arrival of a new virus, now identified as H1N1, in the spring.
It disappeared over the summer, but roared back with a vengeance in August.
"Will there be later disease, and if so, will it be more severe?" CDC acting director Dr. Richard Besser asked on Monday.
"There is no doubt in my mind that CDC, the Department of Homeland Security, and the Health and Human Services Department will use the lull to get ready," said risk communications consultant Peter Sandman, who has taken a special interest in pandemic flu.
"They will stay focused on this problem. They will continue to get ready for a possible pandemic in the fall."
Many public health experts also remember the 1976 swine flu outbreak that wasn‘t.
Manufacturers raced to make a vaccine and 40 million Americans were vaccinated amid a monster public relations campaign. But the flu never spread.
"One big difference between then and now was that when the swine flu was detected in 1976, it was found at a single military installation in Ft. Dix, New Jersey," said Dr. Harvey Fineberg, president of the Institute of Medicine and author of "The Epidemic that Never Was."
"In the ensuing weeks and months it was not detected elsewhere -- not elsewhere in New Jersey, not elsewhere in the United States, not elsewhere in the rest of the world."
Worse yet, some people developed a rare neurological reaction to the vaccine called Guillain-Barre syndrome. Even now, a considerable minority of people believe that vaccines are harmful.
In contrast, said Fineberg, this virus spread globally in a matter of weeks, carried by holidaymakers and jet travel, and has shown it can be transmitted from one person to another.
"Last week the lesson is we got lucky," said Sandman. "We have no reason to think we will stay lucky."
He hopes the alarm bells will continue to ring, at an appropriate level.
"I just hope the government is more worried about the public being caught with its pants down than the government being called fearmongerers," Sandman said.
Fineberg agreed. "One thing we have learned about flu is we should not be surprised by anything," he said.
(Reporting by Maggie Fox)