The U. S. Food and Drug Administration (FDA) approved a new high-dose vaccine in 2010 that is designed to better protect seniors from seasonal influenza.

People older than age 65 are at highest risk of seasonal influenza, but they typically have the worst response of any age group to the flu vaccine because immune function declines with age, which often prevents vaccines from offering seniors adequate protection.

The  vaccine, called Fluzone High-Dose, contains four times the antigen dose given in a standard flu vaccine. Antigens are the active ingredients in vaccines that prime the immune system to respond when the real threat comes along.

“Elderly persons are at increased risk for complications of influenza.  This is the first influenza vaccine that uses a higher antigen dose,” says FDA Spokeswoman Shelly Burgess.

Previous research from the Center for Vaccine Development at the University of Maryland in Baltimore, had demonstrated that elderly study participants needed this four-fold stronger dose in order to stimulate the same immune response as adults less than age 40.

Fluzone High-Dose is a single injection in the upper arm and was available for the 2010-2011 flu season. It does not contain any new ingredients compared to the standard vaccine, and because it is inactivated, it is considered safe for people with immune systems that have been weakened by illnesses or medication.

In clinical trials, a total of 3,876 individuals 65 years of age and older were randomized to receive either Fluzone High-Dose or Fluzone at multiple centers, and the FDA says the results were promising.

“The data demonstrated that vaccination with Fluzone High-Dose resulted in higher immune responses in older individuals,” Burgess says.

In the study, roughly twice the number of the participants on Fluzone High-Dose as those taking the standard vaccine, 48.6 percent compared to 23.1 percent, had detectable antibodies to an influenza A strain.

The FDA says because of the higher dose, there was an increase in side effects, but they were not serious.

Common complaints during clinical studies included pain, redness and swelling at the injection site, headache, muscle aches, fever and malaise. People with hypersensitivity to egg proteins or people who have had life threatening reactions to previous influenza vaccines, should not be vaccinated with Fluzone High-Dose.

Martin Gorbien, MD, director of geriatric medicine and palliative care at Rush University Medical Center in Chicago says he takes influenza in the elderly very seriously and applauds the idea of a new flu vaccine better tailored to seniors.

“There are a number of changes which happen to the immune system with age. They happen to everyone and with that in mind, the idea of having a vaccine that is designed to give a heightened response is a very appealing idea,” Dr. Gorbien says.

But because the study involved here only included 3,800 participants, he’s not sure that’s enough information for him to suggest the vaccine yet to his patients.

“It’s unclear to me if I would be recommending the vaccine without a bit more information,” Dr. Gorbien says. “I think I would want to see more trials.”  But, he adds, “I think there is a very good chance this will turn out to be safe. There’s no doubt that if it adds to the effectiveness of the existing flu shot I think we’re on to something very exciting. “

As part of the vaccine’s accelerated approval process, the manufacturer is required to conduct further studies to verify that the Fluzone High-Dose will decrease seasonal influenza disease after vaccination. The FDA says a large clinical study intended to provide this information is currently underway.