Leading health experts are throwing cold water on Internet-based discussions suggesting "swine-flu parties" as a way to build immunity in children in case the virus mutates into something more severe.

The idea of bringing children with the flu together with others is "a very dangerous practice," Canada's chief public health officer, Dr. David Butler-Jones, said Thursday. While most infections so far have caused mild disease, "you cannot predict which child will get seriously ill and die," Butler-Jones said from an international meeting in Mexico on H1N1 influenza.

"Who wants to have that party, and have that as a consequence? There is no guarantee as to how this virus will evolve. But certainly, trying to get infected at this time is potentially very dangerous."

Reports have surfaced of people discussing, in online forums, plans for swine-flu parties. The parties are based on the belief that, if a person gets a mild version of the virus now, he or she may become less likely to contract a more deadly strain in the next wave of the pandemic.

The idea stems from "pox parties" that were popular before a chickenpox vaccine became available. The idea was to expose children to chickenpox in an attempt to give them immunity to the disease, reducing their risk of getting chickenpox when they were older, when symptoms can be much worse.

Health experts say the idea of throwing a swine-flu party with the same goal in mind is just a bad idea.

"I've got two kids. I wouldn't expose them to this virus," says Dr. David Patrick, director of epidemiology at the B.C. Centre for Disease Control.

"The logic behind it is, people are saying, 'This virus could change and become more virulent, so get exposed to it when it's mild,' " Patrick says. But there is no sign of a "whole raft of crazy mutations going on," he adds.

So far, from a genetic standpoint, the virus appears to be more or less stable, he says. It would take a significant genetic change to increase virulence, "and that typically doesn't happen too fast."

"We're well along in terms of vaccine production, so it's very likely that, by the fall, or at least the late fall, vaccine will be available for Canadians against this strain, which will be a much preferred option than taking the risk of exposing your kid to a live infection," Patrick says.

Reports of swine-flu parties emerged this week in the British media. The founder of mumsnet.com, a parenting website, told BBC Radio she didn't know whether any actual swine-flu gatherings have taken place, but parents are discussing it.

Later, she posted that "a lot of Mumsnetters had suggested that it would be a good idea to catch the strain now," before the virus mutates, supplies of anti-viral drug Tamiflu run out, or health services become strained. "I also said many other Mumsnetters would rather run for the hills than be exposed to swine flu, but that it wasn't irrational to want to get your exposure in sooner rather than later."

In May, Richard Besser, the acting head of the U.S. Centers for Disease Control and Prevention, warned against deliberately exposing people to the virus. And one of the senior people in charge of fighting Toronto's SARS outbreak in 2003 questions why any parent would want to take the risk.

"That you would deliberately take a risk with your child now, because it might avoid a theoretical risk in the future, seem like really odd behaviour, because that's what you're doing," says Dr. Allison McGeer, director of infection control at Toronto's Mount Sinai Hospital.

"We may be concerned that there may be more severe disease in the fall. It's not impossible, but it's not necessarily likely," she says. "1918-19 (the Spanish flu pandemic) has happened only once in the history of the world, and it seems unlikely that it's going to happen again.

"Sure, swine flu is relatively mild in most people. But people have died from it. . . . Kids have died from this."

The Public Health Agency of Canada warned this week that serious cases are occurring in previously healthy people, where the infection rapidly progressed to severe illness requiring ventilators.

Young children are also "probably the most important vectors" for spreading the disease to others, Patrick says, including people at high risk for complications, such as adults and children with underlying asthma, diabetes and other medical conditions, as well as pregnant women.

As of June 29, a total of 7,983 laboratory-confirmed cases of H1N1 flu virus had been reported in Canada. To date, 538 hospitalizations and 25 deaths have been reported among lab-confirmed cases.

Most of those infected are under the age of 20.

As of July 1, the number of lab-confirmed cases of H1N1 worldwide stood at 77,201, including 332 deaths, according to the World Health Organization.

WHO's director general, Dr. Margaret Chan, in a keynote speech to a high-level meeting on H1N1 this week in Cancun, said that officials are getting a "better grip" on warning signs that can signal the need for immediate medical attention. Those signs include difficulty breathing, shortness of breath, chest pain and severe or persistent vomiting.

In adults, a high fever that lasts more than three days is a warning sign. Lethargy in a child — meaning a child has difficulty waking up, or is no longer alert or playing — is a warning sign, she said.

Butler-Jones said Canada has enough anti-viral drugs to treat at least 25 per cent of the population.

"The vast majority of people do not need treatment. I think we're in a good position with what we've already stockpiled."