Vitek said that only recently did the department start tracking flu outbreaks specifically in nursing home facilities, so when confronted with the severe outbreak, they consulted Colorado health officials, who have done so for many years. "Their take is this is very normal because they are dealing with a very vulnerable population in a crowded environment, and a lot of these people are in hospice," she said.

About 40 percent of the residents sickened in the outbreak had been vaccinated this year against flu. It's not known how many of the staffers who became ill had received a vaccination.

Each year, influenza experts predict what kind of flu will circulate the next year, so that a vaccine can be made up. It typically features two A strains and one B. This year, it was not a great match, CDC officials said last week. It's a good match to just under half the flu currently circulating. Still, they said, it's important for people who have not had their flu vaccine to get one, since it provides some protection with even a suboptimal match.

The flu vaccine is particularly important for people who are elderly, since they are more prone to complications of the disease. But it's not as effective for them, according to Dr. John Kriesel, infectious disease expert at the University of Utah School of Medicine. "They just don't make as good an immune response," he said. That's true of other vaccines, as well. Most are "somewhat effective in the elderly, but probably less effective than in younger populations."

The vaccine this year is a good match for influenza A sub-strain H1N1, the old Spanish flu. But the B strain circulating and the A sub-strain H3N2 are "not optimally matched," Kriesel said.

Most of the flu isolates this year have been H3N2.

Kriesel also strongly encourages anyone who has sudden onset of fever, headache and muscle aches, followed by a cough, to seek treatment immediately. The antivirals only help if given within two days of onset. "It clearly reduces the number of days of symptoms and it can be dramatic," he said.

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E-mail: lois@desnews.com