CHICAGO | When the World Health Organization declared the official end earlier this month of the H1N1 influenza pandemic, few people mustered a shrug.

No one stopped the presses. No one threw a parade. Less than a year and a half after "swine flu" infected the public imagination with apocalyptic fears, the virus -- and the short-lived hysteria it spawned -- is already a footnote, a historical blip, a one-hit wonder.

Although H1N1 infected millions worldwide, leaving thousands dead, the crisis mentality faded quickly because influenza annually infects millions and kills thousands.

"The death rate wasn't really that different overall," said Dr. Michael David, an epidemiologist and historian of medicine at the University of Illinois at Chicago.

Despite early reports of unusual virulence and alarming transmissibility, David said, last year's pandemic strain turned out to be only marginally more contagious -- and probably slightly less lethal -- than the average seasonal flu.

"But the way it did differ was that many more children died than in previous years," he said. "They calculated that there was four times the number of pediatric deaths than the average over the past five seasons."

David said the sudden emergence of a novel virus probably explained the high rate of mortality among children and the flu's milder impact on older patients. H1N1 has not circulated widely since 1957-58, when a pandemic strain of H2N2, another influenza A virus, displaced it. That H1N1 virus descended from the strain that caused the Great Pandemic of 1918, which killed tens of millions of people worldwide.

"Whenever you get a pandemic, what's been seen historically is that the old strain gets replaced by the new strain and the old strain goes away," he said. "It's sort of a mystery why that happens. The new one is probably more fit and has a greater number of people who are susceptible to it. There's some limited evidence that people don't get infected by two strains at the same time; so if one is moving faster, it ends up being more successful."

During the pandemic of 1968-69, an H2N3 strain replaced the H2N2 of 1957. H2N3 remained the dominant strain of seasonal influenza until last year's pandemic, which may partly explain why the 2009 pandemic strain was so mild among adults: H2N3 tends to be somewhat deadlier than H1N1 strains, David said.

Epidemiological data now show last year's novel H1N1 virus replacing the older strains of influenza A, he said, although the less common influenza B is still circulating.

"Looking at the historical data, we expect it to become the dominant strain going forward," David added.

The mildness of the virus has critics questioning the all-out response that both fueled and reflected flu hysteria. Dr. Philip Alcabes, an epidemiologist at Hunter College in New York and the author of last year's "Dread: How Fear and Fantasy Have Fueled Epidemics From the Black Death to Avian Flu," described the pandemic as a boondoggle.

"The declaration of the pandemic turned out to be the goose that laid the golden egg for pharmaceutical companies and drug manufacturers," Alcabes said. "That word carries with it such cachet that governments around Europe and North America moved a great deal of public taxpayer money into private, corporate hands to buy products to stave off the coming plague.

"I don't think that was an accident," he added. "I think one of the reasons why certain events are called epidemics, or in this case pandemic, is in order to create that kind of fuss."

The World Health Organization, Centers for Disease Control and Prevention, and other public health organizations use "pandemic" as a term with a discrete meaning, David said. He said public health officials were not necessarily aware of the effect the word would have on the press or the wider public.

"The criteria for a pandemic have nothing to do with how deadly a virus is," David said. "It has to do with a new virus spreading into new populations simultaneously. There actually are specific epidemiologic criteria."

Alcabes said that whatever the technical definition of the word, public health officials had to have known how the public would react to the prospect of a pandemic.

"They knew exactly what 'pandemic' would mean to people," he said. "And I think we got to see a little bit about how those agencies think."

Flu fears fueled a crisis response, including a coordinated drive to mass-produce both the seasonal influenza vaccine and the H1N1 vaccine.

"There were two vaccines last year, which is the first time that's ever happened," David said. "They ramped up production to get the regular seasonal vaccine out by the end of the summer, which was really a Herculean effort to finish it three months earlier than usual. Then they used those facilities to make the new vaccine."

The U.S. government alone spent about $1.6 billion to deploy 250 million doses of the vaccine, according to Alcabes -- "almost enough for every man, woman and child."

"And there's no evidence that mass immunization against influenza makes any difference at all to the severity of influenza outbreaks each year," Alcabes said. "It's an important clinical intervention to be administered to people who, if they were to get infected with flu virus, are likely to experience severe or fatal disease. So did it make sense to offer vaccine to pregnant women? Yes, I think so. But I don't understand how that connects to the idea that everyone in America should be vaccinated."

David agreed that the vaccine had "little to do with the shape of the death curve." He said vaccine shortages had forced the government to ration it in the early stages of the pandemic so that high-risk groups would have access. By the time the H1N1 vaccine became widely available, not many people were scared enough of the apparently mild strain to seek out the vaccine.

But antiviral drugs were another matter.

"Tamiflu was used like water," David said. "In England, because you need to take Tamiflu within 48 hours if you want it to work, they had an automated system that would automatically release Tamiflu prescriptions, and they gave out up to 40,000 doses a day at the height of the pandemic last summer. In Japan, the sewage effluent was found to contain Tamiflu in measurable quantities."

Widespread use of Tamiflu led to concerns that the virus would evolve drug resistance, but David said the feared mutations never materialized. The H1N1 virus developed drug resistance in only a few cases - nearly always in an immune-compromised patient who had undergone an extensive Tamiflu regimen - and almost never passed from one patient to another. David said experts suspect that the same mutations that allow influenza to resist Tamiflu also make it less contagious.

"Essentially, when [a virus] gets a mutation that makes it resistant to a drug, it can't multiply as fast, or it can't defend yourself as well, or it can't get resources as well from its environment," he said.

But Alcabes said that by mass-distributing these drugs, officials flirted with public disaster while pharmaceutical companies reaped private profits.

"The manufacturers of the antivirals made a huge amount of money, and there's not a shred of evidence that those things are of public health value," he said. "They were intended as lifesaving interventions for people who experience very severe respiratory distress because of influenza infection, but that's not the same thing as administering them to a population base."

Alcabes stressed that he doesn't see the entire H1N1 response as overblown. He said the "classical public health intervention," with its emphasis on hand washing, informational advisories, and providing hygienic infrastructure - soap, warm water and towels - was effective, well-executed and worth the money.

"If your main interest is protecting people against a respiratory virus, rather than making money for some private companies, that's what you do," he said.