BMJ 2014;349:g7530 doi: 10.1136/bmj.g7530 (Published 5 December 2014)

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NEWS Early signs show that 2014-15 flu season may be severe, CDC warns Michael McCarthy Seattle

The most common influenza viruses causing illnesses so far this year are seasonal H3N2 influenza A viruses, which in the past have been associated with severe flu illnesses and high mortality rates, the US Centers for Disease Control and Prevention (CDC) said on 4 December. And about half of the H3N2 viruses that have been analyzed show genetic changes that may make this year’s vaccine less effective, it said.

“We know that in seasons when H3 viruses predominate, we tend to have seasons that are the worst flu years, with more hospitalizations from flu and more deaths from the flu,” said Tom Frieden, CDC director, in teleconference with reporters. Anyone who has not yet been vaccinated should be vaccinated immediately, Frieden said, and anyone at high risk of complications should receive prompt treatment with the antiviral drugs Tamiflu (oseltamivir) and Relenza (zanamivir) if they develop symptoms. People at high risk from influenza include children under 5, especially those under 2; adults age 65 and older; pregnant women; and people with chronic health conditions such as asthma, diabetes, heart or lung disease, or kidney disease.

The small genetic changes in the H3N2 viruses were first detected in late March 2014, after the World Health Organization

had selected the viruses that would be targeted by this season’s vaccine.

Frieden said, “We continue to recommend flu vaccine as the single best way to protect yourself against the flu. Vaccine will protect against the strains that are covered in the vaccine and may have some effectiveness against the drifted strain.” Influenza viruses are constantly changing, and such “genetic drift” is common.

He added that prescription antiviral drugs had been “greatly underprescribed” and that less than a sixth of people who were severely ill with flu were getting treatment with antiviral drugs. “That’s the single most important message of this telebriefing,” Frieden said. “We need to get the message out that treating early with the drugs makes the difference between a milder illness [and] a very severe illness.”

He acknowledged that the effectiveness of oseltamivir had been questioned but said that CDC scientists had reviewed the full data set and had found “strong” evidence that the drug, if given early in the illness, reduced the duration of illness. “It is not a miracle drug, but we believe it is an effective drug,” he said. Cite this as: BMJ 2014;349:g7530 © BMJ Publishing Group Ltd 2014

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Early signs show that 2014-15 flu season may be severe, CDC warns.

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