As the nation braces for one of the worst outbreaks of influenza in several years, major drug manufacturers are reporting a shortage of the vaccine.

Tamiflu and Fluzone - the two most-common vaccines on the market - are both being reported as being in short supply.

Roche Holding AG told Reuters late on Wednesday that it had a shortage of the liquid formulation of Tamiflu, which is used mainly to slow down or stop the symptoms of the flu in children already infected with the virus.

Sanofi SA, the largest flu vaccine provider in the United States, said on Thursday that it had sold out of four of its six formulations of its Fluzone seasonal flu vaccine due to the unanticipated late-season demand for vaccines.

Peak levels are cresting for victims that have come down with the flu, and the drum makers are taking the necessary steps to assure supplies of the vaccines.

"We are hearing of spot shortages. Given the time in our flu season, it isn't surprising. People who haven't been vaccinated and want to get the vaccine may have to look in several places for it," CDC spokesman Tom Skinner said on Thursday

It is not unusual to run out mid season during a moderate to severe season, which is what this year looks like, he said.

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