Flu season is winding down, but research on the value of a yearly vaccine goes on. If you are older, your body may respond differently to the influenza vaccine, according to a new study. For the time being, however, the researchers still urge everyone to get vaccinated, even those of a certain age.

"Basically, we started this trial because the Centers for Disease Control tells everyone to get the flu vaccine every year, but less is known about how people in different age groups react to the vaccine," Jenny Jiang, the lead author of the paper, tells TheDoctor.

The number of distinct antibody types in the immune system declines with age. So the immune systems of older persons have fewer specific types of antibodies with which to meet the challenge of the dead or disabled virus in the influenza vaccine.

Jiang and her colleagues analyzed the types of antibodies present in blood samples drawn from volunteers who were immunized with the 2009 or 2010 seasonal influenza vaccines. Study participants were recruited from three age groups: children eight to 17 years of age, young adults 18 to 30 years of age, and older persons aged 70 to 100 years.

Using DNA sequencing technology, the researchers found that the number of distinct antibody types in the immune system declines with age. So the immune systems of older persons have fewer specific types of antibodies with which to meet the challenge of the dead or disabled virus in the influenza vaccine.

The immune system cells, or B cells, that secrete antibodies in response to the influenza vaccine are specialized plasmablasts, the precursor stem cells, Jiang reports. The researchers grouped the progeny, or clones, of these original B cells according to their ancestor, as a way of comparing the number of original B cells among the three different age groups.

"We were surprised to see that the elderly have a reduced clonality," Jiang says. Having fewer clones suggests that for older persons, the pool of B cells that the body has to draw on in response to the challenge of a vaccine is smaller.

The researchers also found that older persons have more mutations of their antibody genes even before they receive the vaccine. This suggests, according to Jiang, that in older persons, through either previous vaccines or infection, the antibodies against influenza viruses or vaccines are already fine-tuned.

So the question becomes, Will older persons have the same ability to respond to a vaccine that changes every year? Jiang asks. "And from the preliminary data, we think that ability may be reduced." The findings highlight the immune system differences between different age groups and may also help manufacturers develop vaccines targeting the elderly.

But that does not mean that older persons should forgo the vaccine, because it is still the best way to prevent influenza declares Jiang, an assistant professor in the department of biomedical engineering at the University of Texas at Austin. Older people should probably get the vaccine early, and if they develop flu-like symptoms, seek medical attention.

The study was published recently in Science Translational Medicine.