The high-dose flu vaccine is significantly better than the regular flu shot at boosting the immune response to the flu virus in frail, older residents of long-term care facilities, according to the results of a University of Pittsburgh School of Medicine study.

It is the first evaluation of the vaccine in long-term care residents, which is the population most vulnerable to flu-related death. The study, published in the Journal of Infectious Diseases and funded by vaccine-maker Sanofi Pasteur, found that -- with the exception of one strain of flu circulating in the 2012-2013 season -- the high dose flu vaccine helped participants mount a better immune response to influenza than the standard flu shot.

"The elderly living in long-term care facilities have higher influenza exposure risks, lower immune defenses and a much greater likelihood of flu-related death than the general population," said lead author David A. Nace, M.D., M.P.H., director of long-term care and flu programs in Pitt's Division of Geriatric Medicine and chief medical officer for UPMC Senior Communities. "For these reasons, we need more effective flu vaccine options for frail, older adults."

Each year in the U.S., there are 3,000 to 49,000 influenza-associated deaths, with over 90 percent reported among people aged 65 years and older, according to the U.S. Centers for Disease Control and Prevention.

Mortality is 16-fold higher among those 85 years old compared to those 65 to 69 years. Although the influenza vaccine is the best defense against the flu, it is not 100 percent effective. Among the elderly population, clinical efficacy of the standard vaccine is reduced by 17 to 60 percent.

"In a separate randomized controlled trial of community-dwelling adults 65 years of age and older, Fluzone High-Dose vaccine induced higher immune responses and provided superior protection against laboratory-confirmed influenza illness compared with standard-dose influenza vaccine," said David P. Greenberg, M.D., vice president of scientific and medical affairs and chief medical officer at Sanofi Pasteur U.S., the makers of Fluzone High-Dose.

"We are pleased to see the results of this new randomized study demonstrating that the higher immune response to Fluzone High-Dose vaccine extends to frail, older residents of long-term care facilities."

In December 2009, the U.S. Food and Drug Administration licensed trivalent inactivated influenza vaccine -- Sanofi Pasteur's Fluzone High-Dose -- specifically designed for people 65 years and older. The high-dose contains four times the antigen of regular shots. Antigen is the part of a vaccine that prompts the immune system to make antibodies against flu.

During the 2011-2012 and 2012-2013 flu seasons, Dr. Nace and his colleagues followed 187 people with an average age of 86.7 years living in 15 community-based, long-term care sites in western Pennsylvania, including nursing facilities, assisted or personal care homes, and independent living facilities.

To ensure they were among the frail population most vulnerable to flu, only people who needed full or partial assistance in at least one daily self-care activity, such as dressing or grooming, were included.

Participants were randomly selected to receive either a high-dose or standard flu shot at the beginning of the flu season. They were then tested for their antibody response 30 and 180 days after receiving the flu shot. This helped doctors determine how much the vaccine prepared participants' immune systems for the flu virus and also how much that protection waned by the end of the flu season.

Both the high-dose and standard flu vaccines contain inactivated versions of the three influenza strains that world health officials determine most likely to be circulating in a given flu season. At 30 days and again at 180 days, the immune response was greater for high-dose compared to the standard vaccine for all the flu strains in both seasons, except strain A/H1N1 in the 2012-2013 season.

The researchers noted that A/H1N1 was identical in both seasons, and 26 percent of participants took part in the study both seasons, something that might have caused the lower generation of antibodies to the strain in the second season.

"Historically, the protection from regular influenza vaccine among seniors has been moderate," said senior author Richard K. Zimmerman, M.D., M.P.H., professor in Pitt's Department of Family Medicine. "Now an option with better immunologic protection is available, as our study shows."

The trial did not evaluate whether fewer of the high-dose recipients actually contracted the flu than those receiving the standard vaccine.

"The high-dose vaccine is not a guarantee against contracting the flu, even though it significantly decreases the likelihood," said Dr. Nace.

ss"That is why it is so important to take a 'bundled approach' to preventing flu in long-term care facilities, including vaccination of health care workers, asking people with flu-like illness not to visit residents, practicing proper cough etiquette and hand hygiene, and frequent sanitation of commonly used areas and equipment."