Medical experts and world leaders seems to be at odds as to the severity of the new H1N1 virus, with some experts saying it's no worse than your average seasonal flu.

In Mexico, where swine flu is confirmed to have killed at least 16 people, the health secretary voiced optimism that the infection rate was levelling off. Of 219 relatives in contact with 86 suspected swine flu patients, just four have turned up as probable cases.

"Apparently, the rate of attack is not as wide as was thought," said Jose Angel Cordova, Mexico's health secretary.

Peter Palese, a flu expert at New York's Mount Sinai Medical School, said he saw no reason to believe the virus was particularly lethal and said it was behaving more like a garden-variety flu that strikes every winter.

"There is no real reason to believe this is a more serious strain," said Palese, adding that many adults probably have immune systems primed to handle the virus because it is so similar to another common flu strain.

Even in Canada, where there are 55 confirmed cases, the country's chief public health officer found reason to be optimistic.

Dr. David Butler-Jones pointed to the extremely mild nature of the Canadian cases and the fact all the patients were recovering. However, he cautioned that the virus could yet mutate into a more severe form.

Officials at the World Health Organization are taking no chances in their response though.

Dr. Keiji Fukuda, of the WHO, said it's far too early to determine whether Mexico's situation is stabilizing.

Fukuda said the possibilities of what the virus will do runs from fizzling out to causing a global outbreak of severe disease and death.

In the U.S., where hundreds of schools have been closed in several states, President Barack Obama said the government's effort to fight the H1N1 flu strain was justified because the virus is so new and poorly understood.

In his weekly radio and internet address, Obama said the human-to-human transmission creates the potential for a pandemic and that's why the U.S. was acting "quickly and aggressively."

The president noted that the strain can be defeated by a course of antiviral treatment that's already on hand.

Worldwide, there are now more than 600 confirmed cases in 15 countries.

Ottawa, for its part, is launching a website to spread its message about flu prevention.

FightFlu.ca has information about symptoms, travel warnings, and what you can do to trim the chances you'll become infected. The government is also using Facebook, Twitter, and YouTube to get the message out.