Despite evidence that swine flu viruses are circulating in at least three countries, the World Health Organization said yesterday it needs more time to decide whether to raise the pandemic alert level.

Canada joined Mexico and the United States on the list of countries with confirmed cases, with Nova Scotia and British Columbia reporting a total of six cases. All have had mild disease and are recovering. There were reports as well that Spain and New Zealand have suspected cases.

Dr. Keiji Fukuda, the WHO's acting assistant director general for health security and environment, said the emergency committee that advises the WHO's director general on whether to raise the pandemic threat level or declare a pandemic will convene again tomorrow, unless new developments require an earlier meeting.

quot;We want to make sure we are on pretty good, solid ground,'' he said in a teleconference from Geneva.

The discordant disease pattern -- mild in the U.S. and Canada, more severe in Mexico -- is puzzling influenza experts and making it difficult to see what it truly going on. Adding to the confusion is the fact that genetic sequencing of viruses from the U.S. and Mexico show the same strain of the influenza A H1N1 swine flu is responsible for the illness.


Officials tried to prepare people for the idea that it is early days and the mild illness currently being seen in the U.S. and Canada is unlikely to be the whole picture.

quot;Just because we're having mild cases nobody should take this for granted in any way,'' Dr. David Butler-Jones, Canada's chief public health officer, said at a news conference yesterday.

quot;No one should lull themselves into thinking that everything's just fine because it's a relatively mild disease.''

International authorities as well suggested people should prepare themselves for continued spread of the virus, the possibility of school closures as the virus hits new communities and that deaths are likely to occur.

quot;Of course, we may be fortunate and not have them,'' said Dr. Anne Schuchat, interim deputy director for the science and public health program at the U.S. Centers for Disease Control.

quot;But I think we really need to prepare for the idea that we will have additional cases . . . and I do fear we will have deaths here.''

The acting head of the CDC, Dr. Richard Besser, said people should start making plans for how they can cope when the virus reaches their communities, for instance how they would handle child-care arrangements if their children's schools were closed.

He suggested authorities are in discussions with vaccine manufacturers exploring the option of making a vaccine against the virus. Among the ideas being explored would be to add a fourth component to the existing flu shot, which is designed to protect against two subtypes of influenza A and one family of influenza B viruses.

Schuchat also revealed that testing being done at the CDC suggests seasonal flu shots probably don't offer protection against this virus.

Flu shots contain a component to protect against human H1N1 viruses. While swine viruses have the same name, they are genetically very different, experts say.

quot;The tests that we've done so far against the seasonal flu vaccine of H1N1 is very pessimistic. It does not look like there's cross-reacting antibodies from the seasonal vaccine . . . to this particular virus,'' said Schuchat.

She said work is ongoing to see whether having been infected with H1N1 flu viruses in the past would confer any immune protection against the swine flu viruses.

Fukuda, the WHO's acting assistant director general for health security and environment, said teams from the WHO, Canada and the CDC are in or are heading to Mexico to help public health authorities there try to figure out why the pattern of disease appears to be so different.

The United States has reported 20 cases, and Mexico's health authorities say the disease has killed up to 103 people in his country and likely sickened more than 1,600 since April 13.

It has been reported that in Mexico a large percentage of the cases are in people in their 20s, 30s and 40s, a demographic not generally hard hit by flu.

Officials haven't ruled out the possibility that some other viruses are causing some of the illness there, though there are no reports that they have found any other likely culprit.

Fukuda said people should understand that flu viruses change constantly and that the current behaviour of the virus is no guarantee of its future actions.

quot;It's quite possible for this virus to continue to evolve. So when viruses evolve, clearly they can become dangerous for people, that is to cause more serious disease,'' said Fukuda, whose specialty is influenza.

quot;Or they're also able to mutate so that they cause less serious disease. And that's very difficult to predict and it is one of the things we will watch for very carefully.''


He cautioned against predictions about how a pandemic with this virus might play out, if it goes on to become a pandemic strain.

quot;I think we are too early in our investigations to be able to address the lethality of the virus,'' Fukuda said.

quot;Clearly we are seeing reports of cases which are mild . . . and we are also hearing reports about cases in Mexico, although it's a little bit less clear how often these are associated with either fatal cases or serious illness cases.''

quot;I think it's way too early right now to predict whether we might see a mild pandemic or a severe pandemic.''

GRAPHIC: Photo: DARIO LOPEZ-MILLS, ASSOCIATED PRESS , People look up toward an image of the Virgin of Guadalupe, Mexico's patron saint, at the Basilica of Guadalupe in Mexico City yesterday. Most churches stood empty in the city after services were cancelled, and health workers screened airports and bus stations for people sickened by a new strain of swine flu that experts fear could become a global epidemic.