Closing schools, stopping large gatherings and other such measures are unlikely to do much to prevent the spread of the H1N1 swine flu pandemic, a team of experts predicted.
They said pandemic closely resembles the pandemic of H2N2 influenza in 1957 when it quickly became apparent that there was little officials could do to stop it.
"Efforts to mitigate it were futile," Brooke Courtney Center for Biosecurity at the University of Pittsburgh Medical Center said in a telephone interview.
Federal officials are expected to announce their recommendations for school closures on Friday. Local school districts and states usually make the decision to close schools, but they look to the federal government for advice.
At the height of the epidemic in May, more than 700 schools closed in the United States, according to the Department of Education.
In Mexico, where the pandemic started, officials closed government offices and schools for around two weeks in April and May, and encouraged businesses to close.
H1N1 is still circulating and, just as influenza did in 1957, it is dominating the mixture of viruses in the southern hemisphere's flu season going on now.
In its latest update last week the World Health Organization reported 162,230 confirmed cases and 1,154 deaths. But flu experts said this probably reflected only a fraction of the true count as not every patient can be diagnosed with a lab test.
Experts expect the flu will pick up activity in the northern hemisphere's autumn and the WHO predicted one third of the world's population -- two billion people -- will eventually be infected.
Governments are taking different approaches to slowing the spread of the virus. Last month, British experts on the spread of disease said closing schools at the first sign of a new pandemic might delay the worst so health officials can prepare, but cannot prevent the spread of the disease.
Writing in the journal Biosecurity and Bioterrorism, Courtney, Dr DA Henderson and colleagues said it appears that the new H1N1 is now too widespread to try to stop.
"In 1957 it was decided pretty early on that efforts to quarantine or isolate people would not be effective," Courtney said.
As happened this year, the virus first appeared in the northern hemisphere's spring. It worsened in the fall. "The opening of schools in September appeared to be a major factor in initiating community epidemics," the researchers wrote.
"Schools were not closed for the purpose of trying to control the spread of disease. They were closed because too many teachers or administrators or students were out," Courtney said.
In 1957, 25 percent of the US population became ill. Global health experts estimate two million people died.
"What we saw was that the federal government took very practical steps to deal with the expected pandemic in the fall in 1957," Courtney said. "They understood that, yes, it was expected that there would be a lot of people who got sick."
In 1957 it took months to make a vaccine and then it was not very effective, the researchers found.
Drug companies have started making vaccine against H1N1 swine flu. But the recommended population of 160 million people, including healthcare workers and pregnant women, cannot be fully immunized until December, experts estimate. Two doses are needed for full protection.