Influenza vaccine is effective in older adults who are not frail but is less protective in those who are frail, according to a new study.
The smaller amount of protection the vaccine offers in frail individuals is nevertheless worthwhile, Melissa K. Andrew of Dalhousie University in Halifax, Canada, the study’s lead author, told Reuters Health by email. “The frailest people are the most vulnerable to things going wrong with complications from the flu, either mortality up front or persistent disease that would really impact their quality of life,” she said. “Anything we can do to reduce that risk would be helpful for them.”
Vaccines can reduce hospitalization and mortality from influenza, but there is some evidence that their effectiveness in older people is limited, Dr Andrew and her team note in their report, published in the Journal of Infectious Diseases, online July 25.
To determine whether frailty influenced the effectiveness of the trivalent influenza vaccine, they studied patients age 65 or older hospitalized during the 2011-2012 flu season. The analysis included 320 influenza cases and 564 controls without influenza.
Cases had less mobility and function (i.e., were frailer) and were less likely to have been vaccinated for the current and previous flu seasons, compared with controls. Patients were categorized into four levels of frailty: non-frail, pre-frail, frail, and most frail.
Overall adjusted vaccine effectiveness (VE) was 58%. Adjusting for frailty only, VE was 58.7%. Adjusted VE was 65.3% for patients age 65 to 75, higher than the 54.4% for patients over 75.
Adjusted VE was 77.6% for non-frail individuals, 51.0% for pre-frail patients, and 59.6% for frail patients. In the “most frail” subgroup, there was no apparent VE, but the sample size was small and the confidence interval was wide.
“Not all older people are frail, and we found that the vaccine was actually quite effective in older people even if they were chronologically older but not frail,” Dr Andrew said. “There are lots of fit older adults in the community who want to stay healthy, and getting an annual flu shot is an important part of healthy ageing. Really that has to do with preventing the consequences of the flu right at the time and, also, the longer-term consequences.”
A flu bout can have a lasting impact on an older person’s health and ability to function independently, she added. “Preventing a hospital stay or illness can have long-term benefits for an older person’s functioning and quality of life.”
“We need to be considering people’s frailty in studies of vaccine effectiveness, but also in our clinical practice," Dr Andrew said, noting that identifying frailty in patients can help physicians provide better care. “I would certainly recommend the flu vaccine for all my patients because anybody stands to benefit."