NEW YORK The flu vaccine may not be very effective this winter, according to U.S. health officials who worry this may lead to more serious illnesses and deaths.

Flu season has begun to ramp up, and officials say the vaccine does not protect well against the dominant strain seen most commonly so far this year. That strain tends to cause more deaths and hospitalizations, especially in the elderly."Though we cannot predict what will happen the rest of this flu season, it's possible we may have a season that's more severe than most," said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, at a news conference Thursday.CDC officials think the vaccine should provide some protection and still are urging people to get vaccinated. But it probably won't be as good as if the vaccine strain was a match.One local doctor, and the Pennsylvania Department of Health, agree."I would still advise everybody to get a flu shot. They are probably talking about flu virus mutating, drifting genetically (from the strain the vaccine was manufactured to fight). But the vaccines there may still have protective effects for other types of flu viruses," said Dr. Craig J. Krause of Tamaqua.The vaccines he uses protect against three or more types."Even if there's been a little bit of a drift in a particular strain, it may still offer some protection," he said.Krause recalls a time several years ago when a completely unexpected strain of flu entered the country, and people had to be re-vaccinated."It does happen periodically. They do the best they can to predict the type of flu strains that will be out there, but unfortunately, the viruses can mutate at any time," Krause said. I would still take the flu shot."The Department of Health continues to encourage anyone 6 months or older to get immunized against influenza that has not already done so."We are aware that the CDC has determined that there are some influenza strains circulating that are not covered in this year's influenza vaccine. Cases are also being reported that do match strains covered in the vaccine. Getting vaccinated against influenza is still the single most effective way to protect yourself and your loved ones," said spokeswoman Holli Senior.Flu vaccine effectiveness tends to vary from year to year.Last winter, the flu vaccine was 50 to 55 percent effective overall, which experts consider relatively good. Among infectious diseases, flu is considered one of the nation's leading killers.On average, about 24,000 Americans die each flu season, according to the CDC.Nearly 150 million doses of flu vaccine, built to protect against three or four different kinds of flu virus, depending on the product, have been distributed for this winter's flu season.Times News reporter Chris Parker contributed to this story.