As flu season looms, this year’s updated vaccine promises better protection against the previously undiagnosed strain that hit older Americans and children especially hard last winter, a top federal health official said Thursday.
Though flu vaccines are normally expected to be 50 to 60 percent effective, last year’s vaccine proved only about 13 percent effective in combating that season’s predominant strain – a mutated form of the virus Influenza A or H3N2, according to Dr. Tom Frieden, director of the Centers for Disease Control and Prevention.
Because last year’s unexpected strain didn’t emerge until September – after the season’s vaccines had already been produced – it “was very poorly matched with last year’s vaccine strain,” Frieden said told a press conference sponsored by the National Foundation for Infectious Diseases.
Annual flu vaccines are designed to reflect the viruses experts expect will circulate in the upcoming season. They are usually deduced by tracking the flu strains from the previous season over the summer and around the world, Frieden said.
Last season reinforced that every flu season is a new experience.
William Schaffner, medical director of the National Foundation for Infectious Diseases
As a result, the 171 million flu vaccine doses produced for this season – 40 million of which have already been distributed – also contain changed components of Influenza B alongside those of H3N2.
“Last season reinforced that every flu season is a new experience,” William Schaffner, the infectious diseases foundation’s medical director, said at the press conference. “Occasionally, flu viruses will change substantially after they are included in the vaccine. This can result in lower than usual vaccine effectiveness, which is what happened last season.”
Last year, the nation saw the highest influenza hospitalization rate among Americans over age 65 since the CDC began collecting the data a decade ago. Frieden said that age group is hit especially hard by H3-type strain.
Adults over 65 accounted for about 61 percent of reported influenza hospitalizations, with about 322 cases per every 100,000 seniors, according to the CDC. The year before, there were about 88 cases per every 100,000 seniors.
Meanwhile, 145 pediatric deaths were reported in 2014, compared with 96 the previous year. But because influenza as a cause of death often goes undiagnosed, the real number is likely much higher, Frieden said.
By including components of H3N2 in this season’s flu vaccine, health care professionals hope to raise vaccine effectiveness against predominant strains back up to the 50 to 60 percent range.
“The vaccine has been updated to better match the strain,” Frieden said. “Because undiagnosed H3N2 was the predominant strain last year . . . this year’s vaccine strand has that subset of the flu in it.”
What would happen if another predominant, undiagnosed strand emerges now, with the vaccine already on the market?
Not much, Frieden said.
“Last year, it (the flu) changed when the vaccine had already been made,” Frieden said. “There is nothing that could have been done.”
However, health care officials have already taken a number of steps to reduce the likelihood of that happening, Frieden said.
Efforts to track the flu around the world and thus better predict seasonal predominant strands in the U.S. have improved, while the typical vaccine production time of six months is being cut down to allow more time for research, Frieden said.
As a second line of defense for anyone already diagnosed with the flu, he recommended using an aggressive prescription of antiviral medications, which tame symptoms and shorten duration by about a day.