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Flu
shots: safer, but less effective for older people
By Shari Roan, Los Angeles
Times
September 22, 2003
Researchers
are working on vaccines to better protect patients most vulnerable to
disease.
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% less effective in older
people.
"We're working on how to fix that," she adds.
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.
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."
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.
About the flu
• An average of 36,000 influenza-related deaths occur each year in
the United States.
• Older people with other health problems are at higher risk for
suffering complications from flu, such as pneumonia and sepsis.
• A yearly flu shot is recommended for people who are at increased
risk for serious complications. These include people age 50 and older as
well as residents of nursing homes and people who have chronic heart or
lung conditions, metabolic diseases, kidney disease or immune system
problems.
• The optimal time for a flu shot is usually October (especially
for high-risk groups, such as people 50 and older) and November.
Source: U.S. Centers for Disease Control and Prevention
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© 2002 Global Action on Aging
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