SAN FRANCISCO – Compared with standard dose inactivated influenza vaccine, high-dose influenza vaccine produced non-inferior hemagglutination inhibition titer responses for all A/H1N1, A/H3N2, and B influenza strains among frail elderly long-term care residents in a recent randomized study conducted during the 2011-2012 and 2012-2013 influenza seasons.
The high-dose vaccine produced superior titer responses for all strains except A/H1N1 during the 2012-2013 season, Dr. Richard K. Zimmerman reported during an annual scientific meeting on infectious diseases.
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A new influenza vaccine may help protect elderly patients against a number of flu strains, Dr. Richard K. Zimmerman reports.
Geometric mean titers were similar in the groups at baseline for both the 2011-2012 and 2012-2013 seasons. At day 30 during the 2011-2012 season, the geometric mean titers in the standard vs. high-dose group, respectively, were 27.9 vs. 67.7 for A/California/07/2009; 9.3 vs. 23.1 for A/Perth/16/2010; and 14.0 vs. 24.8 for B/Brisbane/60/2008. At day 30 during the 2012-2013 season, titers were 51.6 vs. 45.6 for A/California/07/2009; 13.4 vs.25.0 for A/Victoria/63/2011; and 18.7 vs. 25.6 for B/Wisconsin/1/2010, said Dr. Zimmerman, who is professor of family medicine at the University of Pittsburgh, Pa.
A total of 56 and 113 elderly adults participated during 2011-2012 and 2012-2013 study periods, respectively; 34 subjects participated during both time periods. The participants, who had a mean age of 86.7 years, provided venous blood samples for hemagglutination inhibition titers at baseline and were randomly assigned to either the high-dose or standard-dose vaccination group. A follow-up blood sample was obtained and evaluated 1 month after vaccination. No serious adverse events related to vaccination were reported during the study.
The noninferiority and superiority tests were performed separately for the two influenza seasons, because the vaccine formulations for those seasons contained different A/H3N2 and B strains; the A/H1N1 strains were the same during both seasons, which may explain the lack of superiority in titer response for A/H1N1 during the 2012-2013 season, since 34 patients received the vaccine in 2011-2012, as well, Dr. Zimmerman explained.
"We may have been seeing the effects of the prior vaccination," he said.
The findings of this study are of particular interest because more than 90% of influenza cases reported each year occur in patients aged 65 years and older, and each year, between 3,000 and 49,000 influenza-associated deaths occur; the risk of death increases with increasing age, Dr. Zimmerman said at the conference, which are the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society.
When infected with influenza, mortality among those aged 85 years and older is 16-fold higher than the rate among those aged 65-69 years.
Influenza also results in an estimated 226,000 hospitalizations annually, and hospitalization rates among older adults have increased over the past 2 decades, he said, adding that more effective vaccine options are needed for frail older adults.
The high-dose vaccine was approved in 2009 for use in adults aged 65 years and older, but the phase III study that led to the approval was conducted in healthy adults over age 65 years, leaving questions about the applicability of the findings in the frail elderly long-term-care resident population.
Those included in the current study were also over 65 years of age, but were a frail population in need of assistance in two or more instrumental activities of daily living or at least one activity of daily living, Dr. Zimmerman said.
Though limited by the small sample size, the single-blind study design, and the fact that the study was conducted over two different influenza seasons during which two of the three strains tested changed from year 1 to year 2, the findings suggest that the high-dose vaccine is safe and immunogenic in the frail elderly population. How the titer responses seen in this study correlate with clinical outcomes in this population requires further study, he concluded.
This study was funded by an investigator initiated grant from Sanofi Pasteur. Dr. Zimmerman reported serving as a research grant investigator funded by Merck, MedImmune, and Sanofi Pasteur.