A particularly bad flu is sweeping the United States, killing 26 children so far this season and nearly doubling hospitalisations among people over 65 in the past week alone, officials said on Friday.
More virulent variety
The reason is the predominant strain of flu this year is H3N2, a variety that has shown itself in prior years to be more virulent than other kinds.
Even more, the vaccine that is supposed to protect against the annual flu is missing its mark because two-thirds of the H3N2 strains that experts are seeing were not included in this year's flu shot, said the US Centres for Disease Control and Prevention.
Read: Flu (influenza)
"It is shaping up to be a bad year for flu," said CDC chief Tom Frieden in a conference call with reporters.
"H3N2 is a nastier flu virus than the other flu viruses."
At week seven of the typically 13-week flu season, the virus "is now widespread in almost the entire country," he said.
Flu typically infects five to 15 percent of the population. It can be dangerous in those with weak immune systems, including the elderly and children.
Frieden said hospitalisation rates among people over 65 "are rising sharply", going from 52 per 100,000 last week to 92 per 100,000 this week.
"That is high but typical for H3N2 seasons," Frieden said.
The last H3N2 season was in 2012-2013, and the cumulative hospitalisation rate among the elderly that season was 183 per 100,000.
Read: Flu and the elderly
"We wouldn't be surprised to see something similar happen this year," Frieden said.
An update on the effectiveness of this year's vaccine will be released in the coming weeks.
Anti-flu drugs can reduce symptoms
While Frieden said he expect to find the vaccine to be weaker than usual, he said authorities are still urging people to get their flu shot because it may offer some protection against other strains of the flu that are circulating.
He also called for doctors to give antiviral drugs, like Tamiflu, to patients if they get sick.
Read: Tamiflu resistance warning
"In the context of an H3N2 predominant season, with a less effective vaccine, treatment with anti-flu drugs is even more important than usual," he said.
Scientists have found that anti-flu drugs can reduce symptoms, shorten the duration of symptoms and reduce the risk of complications, he said.
"Anti-viral flu medications are greatly under-utilised but if you get the flu and you get medicines early they could keep you out of the hospital, they could keep you from having to go into the intensive care unit and they might even save your life."
Most people do not know the anti-viral drugs exist and fewer than one in five high-risk patients get treated, he said.
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