Though shortages are not unusual, the flu's early arrival and this year's especially nasty strain mean the situation could worsen.

"People who haven't been vaccinated and want to get the vaccine may have to look in several places for it," said Tom Skinner, a spokesman for the Centers for Disease Control in Atl

Sanofi SA, the largest flu vaccine provider in the United States, said on Thursday it had sold out of four of the six different dosages of Fluzone seasonal flu vaccine due to unanticipated demand. The vaccine is made in different sized vials and pre-filled syringes.

"At this point we are not able to make any more vaccine because we are gearing up for next year's vaccine," said Michael Szumera, a spokesman for Sanofi. Because flu strains mutate, vaccine makers must reformulate seasonal flu vaccine every year.

Most conventional flu vaccines in the United States are still made using a 60-year-old process in which the vaccine is grown in fertilized chicken eggs, a method that can take several months to complete. But this is changing.

In November, Novartis won U.S. regulatory approval to sell its cell-based flu vaccine, which uses a speedier manufacturing process. But it is not yet widely available.

AstraZeneca Plc also sells flu vaccines in the United States.

SHORTAGES FOR KIDS

Henry Schein Inc, the nation's largest distributor of flu vaccines to physicians' offices, said it has vaccine available from Novartis for its customers immunizing patients four years old and older.

However, it said "we do not have the pediatric vaccine for children aged six months to four years old due to its unavailability from the manufacturer, Sanofi."

Roche Holding AG has a shortage of the liquid form of Tamiflu, given to children who already have the flu to slow or stop symptoms.

Roche said it told wholesalers and distributors in recent weeks that temporary delays in shipments were imminent. A spokeswoman for the U.S. Food and Drug Administration confirmed that there have been supply interruptions in some locations.

In the meantime, pharmacists can make a substitute by dissolving Tamiflu capsules in a sweet liquid, according to a spokeswoman for Roche's Genentech unit, which makes Tamiflu.

Roche said an unexpectedly severe flu season has also hit Canada and that its government had agreed to lend Roche Tamiflu capsules from the country's emergency stockpile. It noted that the product is especially needed for hospitalized patients and those in nursing homes.

SMALL FINANCIAL BOOST

Karen Andersen, an analyst with Morningstar, said Tamiflu sales would likely more than double to about $750 million this year from about $350 million in the 2011-2012 flu season. Tamiflu demand could boost overall Roche revenue this year by about 1 percent, but she said that would be a "small positive impact" for the company.

Walgreen Co, which provides flu shots in some of its pharmacy locations, said on Wednesday it had given 5.7 million doses so far this flu season, up from 5.3 million a year ago. Walgreens is the largest distributor of flu vaccines in the United States other than the government

Jason Gurda, a healthcare equity research analyst at Leerink-Swann, said in a research report this week that 2,255 flu-related hospitalizations have been reported since October 1, 2012, up 735 from the previous week but below the 6,896 hospitalizations in the 2009-2010 season.

He said that could have a "modestly positive impact" on first-quarter volumes for hospitals and said that many companies, including HCA Holdings and Tenet Healthcare, had hospitals in the states most affected so far.

One small insurer, Centene Corp, in December trimmed its earnings estimates for 2012 because its managed care business in Texas and Kentucky, where the flu struck early in the season, had boosted its medical costs.

HOSPITALS OVERWHELMED

Most of the United States is nearing peak infection levels seen during moderately severe flu seasons, according to the CDC. The agency estimates the percentage of people seeing health care providers for influenza had increased during the previous four consecutive weeks to 5.6 percent. That compares with 2.2 percent the previous year, when flu was mild.

More than 15,000 cases have already been reported in New York State, nearly triple the number last year, though 2011-12 was an extremely mild flu year and not at all typical. Hospitalizations are up 169 percent.

Manufacturers planned to produce 137 million doses of the vaccine and as of late last year, 112 million people had been vaccinated, the CDC said. Sanofi produced 60 million of those doses and GlaxoSmithKline PLC had planned to make 25 million doses.

A spokesman for GlaxoSmithKline said on Thursday it expected to have the vaccine available until mid-February.

(Reporting by Ransdell Pierson, Julie Steenhuysen, Bill Berkrot, Susan Kelly, Scott Malone and Jessica Wohl, Writing by Caroline Humer; Editing by Jilian Mincer, Lisa Von Ahn, James Dalgleish and Dan Grebler)

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