An increase in influenza vaccination rates among patients ages 65 years and over following a health policy change in the United Kingdom did not lead to any decrease in hospitalizations and mortality, a study found.
Researchers studied data from patient surveys and administrative records for adults 55 to 75 years old in England and Wales from 2000 to 2014. A regression discontinuity design was applied to a sharp increase in vaccination rates that followed the 2000-to-2001 flu season, when U.K. health policy prioritized vaccinating people ages 65 years or older. Some people younger than age 65 years were vaccinated, and some older than age 65 years were not, so the study was analogous to a randomized trial with imperfect adherence, the authors noted. Data included 170 million episodes of care and 7.6 million deaths. The results were published March 3 by Annals of Internal Medicine.
After the policy change, the rate of seasonal influenza vaccination among those ages 65 years and older increased 22.8 percentage points (95% CI, 21.7 to 23.9 percentage points) in a database of 100 monitored general practitioners and 19.3 percentage points (95% CI, 15.8 to 22.9 percentage points) in a representative sample of patients enrolled in the National Health Service.
Hospitalization rates were higher for men than for women and increased with age, but the age profiles of hospitalizations for any cause and for pneumonia or influenza were smooth across the age-65 threshold for both genders. When the change in vaccination rate at age 65 years was taken into account, the implied effectiveness of vaccination was −3.9% (95% CI, −8.5% to 0.6%) for total hospitalizations, −5.8% (95% CI, −25.3% to 12.9%) for pneumonia and influenza hospitalizations, −3.6% (95% CI, −11.6% to 4.3%) for respiratory hospitalizations, and −4.4% (95% CI, −11.0% to 2.3%) for circulatory hospitalizations. Mortality rates also showed no significant changes. They were higher for men than for women and increased with age, but the age profiles of all-cause mortality and mortality related to pneumonia or influenza were smooth across the age-65 threshold for both genders.
These findings are subject to less bias and confounding than the estimates from other observational studies in the literature, the authors said. Although vaccinated and unvaccinated people were equally protected by herd effects, the population was roughly half vaccinated, below levels likely to achieve herd immunity and not markedly different from rates in previous studies, they wrote. They noted three health-related factors that might change sharply at age 65 years: frequency of medical visits, employment, and pneumococcal vaccination.
“Therefore, continued vaccination of this population, particularly with high-dose vaccines, seems appropriate,” the authors concluded. “Our findings raise questions, however, about the overall effectiveness of a vaccination strategy that is limited to standard vaccines and focuses too much on elderly persons. Supplementary strategies, such as vaccinating children and others who are most likely to spread influenza, may also be necessary to address the high burden of influenza-related complications among older adults.”