New York City’s medical community spent yesterday feverishly assessing how residents in the five boroughs would be affected by the fact that the much-hyped flu shot would be in short supply this season.

Word of the shortage, which came Tuesday after British regulators unexpectedly revoked the license of pharmaceutical giant Chiron, was fired off in memos and relayed in phone calls, leaving many concerned about an ugly, and possibly deadly, season.

“We are worried because our residents are frail and they are prone to getting the flu,” said the vice president for nursing at the Amsterdam Nursing Home in Morningside Heights, Flor Nebres. Mrs. Nebres said the home, which has 409 residents, was notified yesterday by its Long Island-based pharmacy that flu shot doses were “on hold” until further notice.

The city health commissioner, Dr. Thomas Frieden, said late yesterday afternoon that the city had ordered 90,000 doses of the shot from Chiron, which supplies the nation with about half, or 50 million, of its flu vaccines. Another 140,000 doses were ordered from a competitor.

Dr. Frieden said the city would have enough of the vaccines to inoculate the elderly, who account for 90% off all flurelated deaths, but stressed that healthy should forgo the shot.

“I think people can understand that if there is a limited resource it should go to the people, not who may inconvenienced by a few days of cough and fever and a couple of days missed from work, but to the people who are going to die from it,” Dr. Frieden said during a hastily called phone conference.

Meanwhile, New Yorkers had already started calling private-practice doctors to inquire about whether they would have to skip their annual flushots. Dr. Theodore Strange, an internist who practices in Brooklyn and Staten Island, said his offices, which he shares with other doctors, had received over 100 calls since the federal government announced the shortage.

“How the government and whoever was involved in putting this together did not have procedures in place just doesn’t make any sense,” he said. “We can make bombs that go millions of miles and we can’t make flu shots. It’s just not right.”

The attempt to steer generally healthy adults away from vaccines is an about-face from the previous public message. For the last few years, the city, private hospitals, and non-profit groups have taken on massive campaigns to lure in as many people as possible for vaccines. The shots have been given everywhere from supermarkets to churches to doctors’ offices.

“A month ago they were giving us advisories on all the people who should be vaccinated,” the medical director of the emergency department at St. Luke’s-Roosevelt, Patricia Carey, said. “Now we’re finding out that we’re lucky if we can vaccinate the people who desperately need the vaccine.”

Calculating just how many Chiron doses New York City doctors and hospitals ordered may prove to be difficult. Though some hospitals joined a bulk-purchasing program organized by the Greater New York Hospital Association, many have individual suppliers.

The city, which plans to start administering shots next week, supplies only a tenth of all shots, focusing mostly on the low income. And with only two fluvaccine manufacturers, even institutions that order from the competitor, Aventis, are going to feel the affects of the shortage.

The Continuum Hospital System, which includes St. Luke’s-Roosevelt Hospital, for example, already has its Aventis supply, but was notified yesterday that it will not get another order because remaining doses need to be rationed.

Federal and city health officials said the 54 million flu shots available nationwide should go to people over 65; babies and toddlers between six and 23 months; anyone with a chronic medical condition; pregnant women; nursing home residents; children on aspirin therapy; health care workers who deal directly with patients; and those who live with or take care of babies under six months.

Everyone else should “take a deep breath. This is not an emergency,” the head of the federal Centers for Disease Control and Prevention, Dr. Julie Gerberding said.

When asked whether he was concerned about the fact that only two pharmaceutical companies are supplying the shots, Dr. Frieden said he did.

“This episode demonstrates for the second consecutive year the need to improve our current system for ordering and producing flu vaccine,” he added. He also expressed irritation that Chiron, which was cited for manufacturing problems, immediately posted information about how the incident would affect the company’s profits.

In the last two years there have been problems with the strain of the vaccine produced and a shortage of supplies. Last year, the flu peaked early and led to dozens of pediatric deaths in Colorado, California, and other western states. But the season ended up burning off early and was no more severe than years past.

This year only time will tell. If an unusually high number of patients end up in emergency rooms, already crowded hospitals will bear a tough burden.

“The ideal situation is to have as many people vaccinated as possible,” Dr. Carey said. “That won’t be an option this year. Therein lies the risk.”