According to the Centers for Disease Control and Prevention (CDC), the vast majority of flu deaths occur in elderly patients over the age of 65. Thus, saving lives is one of the main goals of influenza vaccination, and a new study published today in the Journal of Infectious Diseases says that high-dose vaccine may do a better job than its standard-dose counterpart of reducing mortality in this group, at least in H3N2-dominated seasons.
The study was conducted with data gathered from more than 1 million Medicare recipients who received either the standard or high-dose vaccine at community pharmacies during the 2012-13 and 2013-14 flu seasons.
The high-dose flu vaccine was 36.4% more effective at preventing deaths than the standard-dose vaccine among the patients during the 2012-13 flu season, when the H3N2 strain dominated. In 2013-14, when H1N1 dominated, the high-dose vaccine was only slightly (2.5%) more effective, and the difference was not statistically significant.
"Our findings suggest that high-dose influenza vaccines and perhaps other vaccines designed to elicit higher HAI [hemagglutination inhibition] immune responses among older adults may yield the most benefits during seasons when influenza A(H3N2) viruses are widespread," said the study authors, who were from the CDC, the Centers for Medicare & Medicaid Services, and the Food and Drug Administration (FDA).
An impact on hospitalization rates
Besides reducing the risk of death, the high-dose vaccine reduced the chance of influenza-based hospitalizations by 22.1% and influenza-like illness (ILI) by 22% for the 2012-13 season. There was no reduction in hospitalizations or ILIs in 2013-14.
This year's flu season has also been dominated by the same strain, and recent reports from the CDC showed that only about half of all recipients of this year's vaccine have been sufficiently protected from the flu. In the 2012-2013 season, vaccine effectiveness was also about 40%, according to study authors. In those seasons hospitalizations for elderly patients for ILI were higher than average.
When H1N1 or influenza B strains dominated a season, the authors said both high and standard-dose vaccines conferred equal amounts of protection for elderly populations.
Still, the CDC said there's no change to current vaccine recommendations. According to Ian Branam, MA, a public affairs specialist with the CDC's National Center for Immunization and Respiratory Diseases, ongoing vaccination is still recommended as the flu season is expected to last for several more weeks. Elderly patients should be offered the high-dose vaccine, but more important is that they get vaccinated.
"Vaccination is especially important for people 65 years and older, because they are at high risk for complications from flu. Flu vaccination is recommended as long as flu viruses are circulating, so it's not too late to get a flu vaccine," said Branam.
When to use high-dose vaccine?
The high-dose vaccine is an inactivated trivalent vaccine approved for use by the FDA in 2009. It contains four times more antigen than the standard dose (60 micrograms vs 15 micrograms per strain). It has been shown to be more efficacious than the quadrivalent standard-dose flu vaccine in some post-licensure studies, but flu experts caution that there is no consensus about how, or when, to use the high-dose vaccine.
Lisa Jackson, MD, MPH, a senior researcher from the Group Health Research Institute, said the high-dose vaccine is usually more expensive.
"Some health plans don't offer it, but there's no preferential recommendation," said Jackson. "There is some benefit to the high-dose vaccine, but we don't know a lot about it."
Jackson cautioned, however, that high-dose influenza vaccine may be used more broadly than just in elderly patients.
"We know that immune response to influenza vaccine starts decreasing already when someone is in their 30s, and then there's a gradual decline in adulthood," Jackson said. "It seems too 'one-size fits all' to say you can only start to use it after 65."
In a commentary on the study, Arnold S. Monto, MD, of the University of Michigan School of Public Health, said the usefulness of high-dose vaccines shouldn't be overlooked as influenza vaccine technology advances.
"This indicates that improvement in our 70-year-old influenza vaccines is possible, and to get there more quickly we should not ignore older technologies while working on more dramatic advances," Monto wrote.
Mar 2 J Infect Dis study
Mar 2 J Infect Dis commentary