But Jiang's team found that after the flu shot, elderly people had lower numbers of distinct B cell types, compared to young people. That essentially means they had a less diverse array of weapons against the flu.
"We also noticed that B cells from elderly people had a higher level of mutation, or tweaks, to their antibody-coding genes compared to other age groups," Jiang said. That suggests their B cells are already very "specialized" -- and possibly more resistant to further "tweaks" from the flu vaccine.
"This basically confirms what we've believed to be true," Kelley said. "But this is the first time [the research] has gotten to this technical of a level."
Another expert said the study provides helpful new information for researchers.
"We've known for years that older adults don't respond as well to the flu vaccine," said Dr. Andrew Pavia, chief of pediatric infectious diseases at the University of Utah in Salt Lake City. "This gives us some insights into why."
And a better understanding of older people's immune response could help in developing better flu vaccines, according to Pavia, who also chairs the Pandemic Influenza Task Force of the Infectious Diseases Society of America.
Both Pavia and Kelley said that ultimately, what's needed is a flu shot that's more effective for seniors -- and for children younger than 2, Pavia noted.
There is already a high-dose flu vaccine on the market, specifically designed for people age 65 and up. Researchers know it can spur older immune systems to produce more antibodies.
"But," Pavia said, "we don't know yet if that means better protection against the flu after people are vaccinated."
For now, study author Jiang said that older adults can take some extra steps to protect themselves. One is to get your flu shot early, since it takes about two weeks for the body to build up immunity. In the United States,
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