May 18, 2013
Flu reaches epidemic level in US, says CDC
Influenza has officially reached epidemic proportions in the United States, with 7.3 percent of deaths last week caused by pneumonia and the flu, the US Centers for Disease Control and Prevention said today.
That is just above the epidemic threshold of 7.2 percent. Nine of the 10 US regions had "elevated" flu activity, confirming that seasonal flu has spread across the country and reached high levels several weeks before the usual time of late January or February. The other region, the Southwest and California, had "normal" flu activity last week.
This year's flu vaccine is 62 percent effective, scientists reported today in the CDC's weekly publication.
That is considered "moderate" effectiveness and means that almost four in 10 people who receive the vaccine and are exposed to the virus will nevertheless become infected. It is line with the effectiveness of previous years' flu vaccines, which typically range from 50 percent to 70 percent, Dr. Joseph Bresee, chief of the CDC's influenza division, said in a telephone conference call.
Tens of thousands of US citizens die every year from flu, even in non-epidemic years. The CDC in its report did not give a total number of deaths due to flu.
Experts recommend the vaccine for everyone over 6 months of age. Even if it does not prevent flu, immunization can reduce the severity of the illness, preventing pneumonia and other life-threatening results of flu.
Public health authorities were correct in their forecast of which flu strains would emerge this season and therefore what vaccine to make: one that contains two strains of influenza A and one strain of influenza B. An A strain, called H3N2, predominates this season, though the B strain has caused about 20 percent of cases.
About 10 percent of cases have been caused by a B strain that is not in the vaccine, which for technical reasons "has space for only three strains," CDC Director Dr. Tom Frieden said.
"We have a good vaccine but not a great vaccine," Dr. Arnold Monto of the University of Michigan, a co-author of the vaccine-effectiveness study, said in an interview. "Every year we see vaccine failures."
The vaccine is less effective in the frail elderly, in people receiving chemotherapy for cancer, and in people taking oral steroids. That's because their immune systems have been weakened and are often unable to produce an effective number of antibodies in response to the vaccine.
"That's the opposite of what we would wish," Frieden said. "The people most susceptible (to flu) are less likely to get the benefits of the vaccine."