WASHINGTON (REUTERS) - Influenza has reached epidemic proportions in the United States, with 7.3 per cent of deaths last week caused by pneumonia and the flu, the US Centres for Disease Control and Prevention said on Friday.
That is above the epidemic threshold of 7.2 per cent, CDC said. Nine of the 10 regions of the United States 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 US region, the Southwest and California, had "normal" flu activity last week.
The vaccine against the flu strains that were forecast to predominate this year is 62 per cent effective, scientists reported on Friday 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.
Experts recommend the vaccine for everyone over 6 months of age. Even if it does not prevent flu, it 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 against influenza A as well as influenza B.
An A strain, called H3N2, predominates this season, though the B strain has caused about 20 per cent of cases.
"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."
In its weekly flu update on Friday, the CDC reported that 24 states and New York City experienced "high activity" in flu-like illnesses last week. In 16 states, flu activity was moderate, while 10 states reported low or minimal flu activity.
The percentage of visits for flu-like illness, 4.3 per cent, is comparable to that during the 2007-2008 flu season, which was characterised as "moderately severe" but which peaked some two months later.