Flu Shot Cuts Infection Risk By Less Than Half As Virus Spreads

Americans who rolled up their sleeves for a flu shot this year cut their chances of coming down with the aches and fever of influenza by almost half, a level of protection that is disappointing for a vaccine but still better than in some recent years.

As the virus continues to sweep across the U.S. at epidemic levels, vaccine effectiveness level was 48 percent against acute respiratory illness from the end of November through Feb. 4, according to an analysis of 3,144 people enrolled in the U.S. Influenza Vaccine Effectiveness Network.

“The 48 percent overall is not as good as we would like to see for flu vaccine, but the protection we see is significant,” heading off severe illness that requires medical care, said Brendan Flannery, an epidemiologist in the Centers for Disease Control and Prevention’s influenza division.

The findings still suggest the vaccine is much better matched this season than two years ago, the last severe flu outbreak, when the shot was only 1 percent effective against the predominant circulating strain of the virus. The majority of samples tested in U.S. laboratories so far this year are similar to one of the components in the vaccine, offering greater protection than average since 2007, the agency said.

The vaccine was just 40 percent effective in the 2012/2013 season, when a similar strain was circulating, he said. The immunization prevented 60,000 hospitalizations and 2,000 deaths that season, Flannery said. “It’s a big number for what is a moderate level of vaccine effectiveness,” he said.

Most of the flu sufferers this year have contracted H3N2, a strain of the virus known to be particularly hard on the elderly. The good news is the vaccine provides significant protection for people aged 50 to 64 and children under age 8. For the remainder, the benefit could have stemmed from chance. It was lowest for those aged 18 to 49, offering just 19 percent protection overall and 13 percent against H3N2.

The flu remains at epidemic levels in the U.S., accounting for almost one in 20 doctor visits, a portion that has been rising. Influenza and pneumonia were responsible for 7.9 percent of all deaths in the week ending Jan. 21, and 20 children have died so far this year from the virus.

While the most common month for peak influenza activity is January, last year it came in March, said Lynnette Brammer, a CDC epidemiologist. Given what doctors and public health officials are seeing now, there is likely to be a repeat this year, she said, with the caveat that it’s impossible to accurately call the peak until rates start to decline.

“Right now there is still a lot of influenza activity, so there would be a benefit if someone hasn’t been vaccinated to get it now,” she said. “We would certainly expect for influenza activity to continue on for several weeks.”

While 145 million doses of the vaccine have been distributed in the U.S., only a little more than one-third of children and adults under age 65 were immunized by early November. Among the elderly, 57 percent had received the shots, which are made by companies including Sanofi, GlaxoSmithKline, CSL and Protein Sciences.