Why the Flu Shot Is Less Effective for SeniorsThursday, 14 Mar 2013
Flu vaccines protect people by activating white blood cells
that, in turn, boost the development of antibodies to the flu, a
new study suggests.
The finding may lead to more effective vaccines -- especially
for people whose immune system isn't robust enough to fully
protect them from the flu, such as the elderly, the study
authors said.
"It is well known that CD4 T cells are important for the
generation of antibody responses," said lead researcher Dr.
Hideki Ueno, an investigator at the Baylor Institute for
Immunology Research in Dallas.
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"Most importantly, we found that the appearance of these cells
in blood correlated with the development of protective
antibodies against flu. Therefore, these cells appear to be very
important for the successful flu vaccination," he said.
The failure of older people to generate a protective antibody
response after a flu vaccine might be associated with the
failure to produce these CD4 T cells, Ueno said.
This year, for example, the flu vaccine was only 9 percent
effective in older people against the dominant H3N2 strain,
according to the U.S. Centers for Disease Control and
Prevention. Finding ways to boost a vaccine's effectiveness is
especially important for seniors, who are at higher risk of
complications from the flu and are more likely to die from them.
One way to help high-risk people might be to identify those
whose immune response is likely to be insufficient to fully
protect them from the flu, the researchers said.
"You could potentially screen people for their antibody response
-- particularly young children and the elderly," said Andrea
Sant, a professor with the department of microbiology and
immunology at the University of Rochester, in Rochester, N.Y.
This screening could also be important during flu pandemics,
said Sant, who was not involved with the study. "You could find
out if a dose is sufficient to protect people and those who
might need a boost," she added.
Sant said using these CD4 T cells might also be a way of making
vaccines more effective.
"Theoretically, you could fine-tune vaccines so they could allow
people to have more of these cells in their body when they get a
vaccine, either by adding them to a vaccine or administering
them before a vaccination," she explained.
The new study was published online March 13 in the journal
Science Translational Medicine.
Looking at small groups of children and adults, the researchers
found a special type of CD4 T cells that appear after receiving
a flu shot. Specifically, these CD4 T cells have three
components -- called CXCR5, CXCR3 and ICOS -- that are the key
to boosting the immune response to a flu vaccine, the study
authors reported.
These so-called "helper cells" aid what are called "memory" B
cells to make antibodies to the flu. What these memory cells are
remembering is having seen a flu strain before and knowing how
to react by making antibodies, the researchers explained.
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So, in older people who have a lot of these memory cells,
boosting CD4 T cells might help memory cells to respond and
launch an immune defense, the investigators suggested.
"Therefore, it would be very beneficial and important to
understand the mechanisms by which these cells develop in
humans. These studies might lead to the development of more
effective vaccines for flu and other diseases," Ueno said.
Another infectious diseases expert, Dr. Marc Siegel, clinical
associate professor at NYU Langone Medical Center in New York
City, added, "If you could boost this process you could boost
immunity, and this could help the elderly who have an impaired
immune response."
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