SHAFAQNA –This year’s flu season may be severe because the virus strains that are being seen so far aren’t well matched to the current vaccine, U.S. health officials said, prompting concern that more people than usual may be in danger.
The most common virus strain this year is H3N2, which in the past has been linked to more severe flu seasons. About half the H3N2 viruses have mutations that make them different from the one targeted by the vaccine, the U.S. Centers for Disease Control and Prevention said yesterday. Health officials must pick which viruses to include in the vaccination months before the season begins so manufacturers can produce and deliver the doses in time.
Vaccines have an effectiveness rate of 50 percent to 70 percent among adults under 65 in seasons when their components are well-matched to circulating viruses, according to the CDC’s website. In 2007-2008, the vaccine had 37 percent to 42 percent efficiency, leading to one of the three deadliest flu-related seasons in the last decade, according to the agency.
While the vaccine’s ability to protect people this season “may be reduced, we are still strongly recommending vaccination,” Joseph Bresee, the CDC’s head of influenza epidemiology, said in a statement yesterday.
Young children and adults over 65 are most susceptible to influenza. Flu cases began increasing in the U.S. last month, with more than 1,200 reported to the CDC as of Nov. 22.
The CDC estimates the number of people who die each year from seasonal flu ranges from a low of about 3,000 to a high of about 49,000.
As of Nov. 14, about 139.7 million doses of 2014–15 seasonal influenza vaccine had been distributed to vaccination providers in the U.S., the CDC said.
Vaccine manufacturing starts at least six months before the start of the Northern Hemisphere’s winter flu season. Around the world, more than 140 national flu centers track strains of the virus to help forecast the most likely and common versions. The World Health Organization holds two annual conferences, one each for the Northern and Southern hemispheres, to consult with national agencies decide what to include in the three or four strains most vaccines target.
Because of the lag time between the forecast and the flu season, other strains of the virus can arise that the vaccines don’t specifically protect against.
In the U.S., the Food and Drug Administration makes the decisions on the final combination. This season the drugs have been produced by several companies, including GlaxoSmithKline Plc and Sanofi.
The U.S. flu season usually gains momentum in December, first sickening residents in the southern and eastern parts of the U.S., then spreading across the country.
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