(USA TODAY) - Americans could be in for a rough flu season this year, health officials say.
Two factors could lead to more misery than usual.
First, the dominant strain of influenza virus in circulation is H3N2, a type that has doubled rates of hospitalizations and deaths in the past, especially among older people, very young children and people with chronic health conditions, said Thomas Frieden, director of the Centers for Disease Control and Prevention.
Five children have died from influenza this year, Frieden said. Schools and nursing homes have had outbreaks.
Second, flu shots could be less effective than usual because the viruses now beginning to spread around the country aren't a good match for the ones used in the vaccine, according to the CDC, which sent out an emergency advisory to doctors last night.
Four influenza viruses are circulating, Frieden said. About half the H3N2 virus samples tested had major genetic differences from the ones in the vaccine. Other circulating flu viruses are good matches for those in the flu shot.
This could make other methods of preventing flu complications, such as antiviral medications, more important this year, the CDC says. Although antiviral medications such as Tamiflu and Relenza can't prevent the flu, they can make the flu "milder and shorter," Frieden said. He called antivirals a "second line of defense" but said they need to be prescribed within the first couple days of symptoms.
Antivirals are underused. Only one in six people who could benefit actually get them, Frieden said.
Manufacturing effective flu shots is always tricky. That's because the flu vaccine is produced in the spring but won't be distributed until the fall or winter. Scientists sample the flu viruses in circulation and try to guess which ones will still be circulating months later.
Still, CDC officials recommend a flu shot for everyone older than 6 months because even partial protection is better than nothing. All flu shots are designed to protect against three viruses. This year's flu shots also protect against H1N1, which caused the swine flu pandemic in 2009-2010. Manufacturers have distributed 150 million doses.
It's also important for people to wash their hands frequently, cover a cough and stay home when they're sick, Frieden said.
Other experts say that vaccine-virus mismatch doesn't really matter.
Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, has published studies showing there's no relationship between how closely a vaccine matches circulating viruses and its effectiveness.
In his study, "we couldn't find any correlation between the 'good matches' and actual effectiveness," Osterholm said.
Experts note that even people who get the flu shot can still get sick with flu-like symptoms, simply because there are so many viruses that cause similar symptoms. Contrary to misinformation spread on the Internet and elsewhere, flu shots cannot cause the flu.