The best defense
To avoid getting the flu, some workers and others get vaccinated, although at a much lower rate than what federal officials recommend. Only an estimated 40 to 45 percent of people get vaccinated, compared with the CDC's 70 percent goal.
Even among health-care workers, the rate of immunization has lagged what is needed to substantially reduce flu acquired in a hospital or other health-care setting, according to the Association for Professionals in Infection Control and Epidemiology.
Last January, Walgreens was swamped with customers getting flu shots in response to the wide spread of illness, which had already reached its peak in total cases the month before.
"Company-wide for the season we did about 7 million flu shots, but nearly 1.5 million came in the month of January," said Walgreens spokesman James Cohn. "January was crazy."
But those shots may have come too late for many people.
"The CDC recommends getting it as soon as the vaccine becomes available," Cohn said. "It takes two weeks to build up immunity from a flu shot."
This season, Walgreens has seen a big jump in the number of people getting shots early.
Through the end of November, the company's drugstores had administered 6.1 million vaccinations, versus 4.6 million in the same period last year.
"The incentive to get a flu shot is more at the top of mind for some people," said Cohn. Walgreens plans to release updated vaccination data Monday.
The CDC estimated that vaccinations prevented about 6.5 million flu cases and about 80,000 hospitalizations last year.
But Dr. Leonard Friedland, director of vaccines for drugmaker GlaxoSmithKline's North America division, said that while the H1N1 virus "could disproportionately affect young and middle-age adults ... it's those age groups that typically don't think they have to be vaccinated.
"Vaccinations are still available, and that's an important message for your readers," he said. "The best tool to prevent influenza is vaccination."
Friedland noted that new insurance that kicked in Jan. 1 under the Affordable Care Act will enable several million people to obtain vaccinations with no out-of-pocket cost.
But if younger and middle-age adults don't get vaccinated, they could exacerbate the rate of illness.
"If they are going to work and they are sick, they are spreading it to people of the same age," he said.
Vaccines are including a wider variety of flu strains in the hope of providing greater immunity.
This year, for the first time, GSK distributed two forms of so-called quadrivalent flu vaccines, which contain four different strains of flu compared with traditional vaccines containing three strains.
Because it contains an additional "B" strain, Friedland said, quadrivalents "takes the guesswork out of what's required" to fight a strain that becomes prevalent for a given year.
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Friedland said there were an estimated 138 million doses of flu vaccine available nationwide, with GSK providing about 25 million of them.
About 12 million of GSK's vaccine doses this year are the the quadrivalent version. Next season, he said, "we expect to produce almost 35 million vaccine doses for the U.S., nearly all of which will be quadrivalent.
—By CNBC's Dan Mangan. Follow him on Twitter