CDC Director Thomas Frieden, M.D., MPH

Nursing homes and other healthcare providers should prepare for a bad flu season, based on indications that this year’s dominant strain is dangerous and the vaccine might be of limited effectiveness, the Centers for Disease Control and Prevention announced Thursday.

It appears that by far the most prevalent strain of the seasonal influenza virus this year is A H3N2, CDC Director Thomas Frieden, M.D., told reporters on a press call yesterday. This type of flu virus typically is associated with more severe illnesses and worse patient outcomes. There are additional reasons to be concerned this year, Frieden explained. About half of the H3N2 strains that have been identified by the CDC in recent months are “poorly matched” with this year’s vaccine, meaning the vaccine might not offer robust protection.

There are many different types of flu virus, and each year’s vaccine targets only a few that must be selected by experts long before the flu season starts. Another challenge is that flu viruses frequently change at the genetic level. After this year’s vaccine already was developed, some H3N2 viruses became less vulnerable to the current vaccine, Frieden said. He emphasized that people still should be vaccinated, and that the shot could have “some effectiveness” against the newly altered strains.

Frieden said his “single most important message” was that providers should be prepared to promptly administer antiviral medications, particularly to people at high risk for flu complications due to diabetes, lung disease or other health conditions. The antivirals Tamiflu (oseltamivir) and Relenza (zanamivir) combat flu once a person already has been infected, but only about one in six people with severe flu receives them, the CDC leader said.

Doctors might mistakenly believe that they should administer these drugs only after a person tests positive for the flu when in fact they should start the medications immediately if flu is “suspected,” Frieden said. The CDC believes antivirals cut the duration of a severe illness by about one day.

Influenza activity is low but increasing throughout the United States, and outbreaks already have been reported in schools and nursing homes, Frieden said.