The seasonal influenza vaccination reduced flu-related hospitalizations by 56.8% among people aged 50 and older during a recent flu season, according to a report published in Clinical Infectious Diseases.
Even in the oldest age group – the population with the highest risk of developing flu complications and perhaps the weakest immune response – influenza vaccination prevented serious complications, said Fiona P. Havers, MD, of the influenza division, Centers for Disease Control and Prevention, Atlanta, and her associates.
Dr. Fiona Havers
Data on vaccine efficacy in older adults are sparse, and randomized, placebo-controlled trials to gather evidence would be unethical. Dr. Havers and her colleagues studied the issue using a case-control design, focusing on community-dwelling adults aged 50 years and older during the 2010-2011 flu season. They identified 368 patients across 10 states who were hospitalized for polymerase chain reaction–confirmed influenza and matched them for age and county of residence with 773 control subjects.
Hospitalized case-patients were less likely to have been vaccinated (55%) than were control subjects (63%). Thus, the flu vaccine reduced the risk of hospitalization for influenza by 56.8% overall.
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Vaccination reduced hospitalization for influenza by 63.9% in the youngest age group (50-64 years), by 61.0% in the intermediate age group (65-74 years), and by 57.3% in the oldest age group (75 years and older).
These results are similar to those reported in other studies assessing the same time period, including one that evaluated vaccine efficacy in ambulatory adults in the United States and Europe. They also are consistent with the results of observational studies performed during different flu seasons, the investigators said (Clin Infect Dis. 2016 Aug 2. doi: 10.1093/cid/ciw512).
Compared with control subjects, case-patients were more likely to be of nonwhite race, to be of Hispanic ethnicity, to have a lower income, to have had fewer years of education, to have two or more chronic health conditions, to have required recent hospitalization for respiratory problems, to have impaired mobility, and to have lower functional status.
“These findings support current U.S. recommendations for annual influenza vaccination in older adults, especially in adults aged 65 and older who are at higher risk of influenza-associated complications,” Dr. Havers and her associates said.
The Centers for Disease Control and Prevention supported the study. Dr. Havers reported having no relevant financial disclosures; one of her associates reported ties to Genentech, Merck, Novavax, and Pfizer.