The New York doctor who has the President's ear on swine flu warned on Tuesday that the threat this fall is real.

And if you even suspect you're sick, he says, "isolate yourself."

"This flu could be extremely dangerous," said Dr. Harold Varmus, co-chairman of the President's Council of Advisers on Science and Technology. "It needs to be taken seriously."

Varmus is co-author of a stunning report delivered Monday to the White House that says 90,000 Americans could die of swine flu in the coming months.

The 68-page report said about half of all Americans will get the H1N1 virus - and 1.8 million will wind up in the hospital, stressing the health care system.

"The infection rate will be pretty high," he told the Daily News. "Everybody is at quite high risk."

"You should be watching for the symptoms," he said "and stay at home if they're mild. Isolate yourself so you don't spread the virus."

But "if people are feeling quite sick, they should not wait to consult their doctor" and instead head to the hospital.

There are still a lot of unknowns, Varmus admits:
# The new swine flu vaccine won't fully be ready until the virus is well underway.
# There's no guarantee it will even work.
# Experts are not even sure whether it will have to be given in one or two doses.



"I don't know yet," said Varmus. "Until the data is here, we won't know if one or two doses is sufficient. There's a strong history that this virus is different.

"We do think there will be some vaccine available in mid-September, but it will not be nearly enough to vaccinate the entire population," he said.

Varmus says the first to get the vaccine - which takes up to six weeks to be effective - should be health care workers, adults with preexisting health problems, women in late pregnancy and kids younger than 4.

That will mean many people will remain exposed through October and November, when swine flu is expected to come back with a vengeance.

The city Education Department said Wednesday it's preparing for the virus but did not specify how. The city Health Department did not comment on Varmus' new warnings but has previously said that New York is ready.

Swine flu was first detected in Mexico in April. It killed 47 New Yorkers in the spring and sent the city into a frenzy, shuttering schools and jamming emergency rooms. The virus sickened more than 1 million people across the country.

If the new estimate for the number of swine flu hospitalizations in October and November is correct, it could force doctors to put off elective surgeries such as heart bypass or hernia operations, the head of the American Hospital Association said yesterday.

"If you have 1.8 million hospital admissions across six months, that's a whole lot different than if you have it across six weeks," said James Bentley, hospital association vice president.