MEDICAL RESEARCH Age reduces flu shot's effectiveness

As the flu vaccine was made safer, it became weaker.
By SHARI ROAN
LOS ANGELES TIMES
Flu season is just around the corner and, once again, doctors and health officials are urging people older than 50 to get a flu shot.
That advice makes sense -- influenza can take more of a toll as people age. But because the vaccine is less effective in older people, it can fail to protect those who need it most.
"The flu vaccine is better than nothing, but its efficacy isn't that good," says Laura Haynes, an immunologist at the Trudeau Institute, explaining that the vaccine can be up to 60 percent less effective in older people.
"We're working on how to fix that," she said.
She and other scientists at the nonprofit research center in Saranac Lake, N.Y., are trying to figure out how best to tweak the vaccine, making it more likely to prevent the viral infections that kill thousands each year.
Source
The flu vaccine is made from the protein of various strains of dead flu viruses. Over the years, researchers have sought to make the flu vaccine, as well as many other types of vaccines, safer by removing as many components of a virus as possible.
As a result, however, vaccines may not be as effective as they could be, says Susan Swain, president and director of the Trudeau Institute.
"As vaccines got safer and safer, they have lost some of the components that enhanced effectiveness," she says.
In contrast, the smallpox vaccine is made from a weakened strain of the live virus. Although it has some risks, people vaccinated even 50 years ago still may have some immunity to smallpox.
At the Trudeau Institute, which specializes in infectious diseases, Haynes and Swain have identified a component of the immune system that makes it difficult for older people to fight infection, even after they've been vaccinated. And they have proposed tactics to correct the vaccine's weakness.
According to Haynes, the problem for older people begins with lymphocytes called CD4 T cells, which help the immune system work. As people age, these cells' ability to respond to new infections wanes.
In experiments, the scientists have shown that when CD4 T cells from younger animals are transplanted into older animals, the animals are more likely to fight off disease. But when aged T cells are put into young hosts, the immune response decreases.
"The other aspects of the immune system work," says Haynes. "It's the T cells that don't work as well when we age."
Other ideas
The scientists say that returning components of the flu viruses to the vaccine could strengthen the immune response. Another approach, they say, would be to add adjuvants, which a body produces in response to a virus. It's this latter approach that they think holds the most promise.
Cytokines, proteins produced by immune cells, could be one solution. These proteins signal other cells to participate in the immune response. In experiments in mice, adding cytokines caused the aged CD4 T cells to respond better, Haynes says.
Adjuvant research has just begun to blossom in the last five years, says Swain.
"In young people, the vaccines we have work adequately. So there hasn't been a huge impetus to add these adjuvants," she says. "But people haven't considered that it's the elderly who have the poorest response."
The researchers say it will take several more years to bring a more technologically sophisticated, and stronger, flu vaccine to the market. The biggest challenge is making the vaccine more effective while keeping it safe.