FRIDAY, June 5, 2015 (HealthDay News) -- Having acknowledged that the 2014-2015 flu vaccine was mismatched to the circulating influenza strains, U.S. health officials have ramped up next season's shots for broader protection.
Flu-vaccine makeup is determined months in advance so that manufacturers have time to make the millions of doses needed. Components of the coming "2015-16 season vaccine have been changed to more optimally match circulating viruses," the U.S. Centers for Disease Control and Prevention said in its June 5 Morbidity and Mortality Weekly Report.
There also is a version of the flu vaccine called quadrivalent flu vaccine, designed to protect against four flu viruses; two influenza A viruses and two influenza B viruses.
Last year, no one saw until summer that the H3N2 strain would predominate, said CDC epidemiologist Lynnette Brammer.
Work on the vaccine had begun in February, she said. "[The H3N2 strain] came on so fast, and there wasn't time for it to be included in the vaccine," she explained.
As a result, flu shots were only 18.6 percent effective against the predominant H3N2 strain, she said.
Shots for the coming flu season will contain two influenza type A viruses -- H1N1, which caused the 2009 pandemic flu, and last year's virulent H3N2 -- plus an influenza B component, according to the CDC researchers.
These are the strains that appear to be circulating in the United States and around the world, and they're expected to be the main strains in the 2015-2016 flu season, Brammer said.
But there are no guarantees, she cautioned.
"Influenza activity is unpredictable in terms of what virus will predominate and the exact timing of the season, and both of these things, along with others, can have a large impact on season severity," she said. "Therefore, we can't know at this point what the next flu season will look like."
As CDC experts looked back on the flu season that just ended, they described it as moderately severe. Hundreds of thousands of people were hospitalized, and thousands died, most of them 65 and older.
"This year was a severe year, particularly for the elderly. Our vaccine match wasn't as good as we would like it to be," Brammer said. "It was an unusual year."
Deaths from flu ranged from 5 percent to 9.3 percent of all deaths between Jan. 3 and Feb. 21, 2015, the CDC said. That's about average for an H3N2 flu year, Brammer said.
Pediatric deaths were on the high side. The CDC said 141 children died in 40 states. Child deaths usually range from 34 to 171 in a given flu season. The biggest exception was the pandemic 2009-2010 season, when 358 kids died from flu.
The CDC recommends that everyone 6 months and older get a flu shot every year. Brammer said this year's vaccine will be available in September.
"Although we did have a mismatch last season, a flu shot is still the best way to protect against influenza," Brammer said. "We do recommend that come the fall, people should go out and get vaccinated."
For more on flu, visit the U.S. Centers for Disease Control and Prevention.