Non-inferiority Study of Adjuvanted vs. High Dose Flu Vaccine in Residents of Long Term Care

As the primary endpoint, this trial is be using pre- to post-vaccine changes in HAI titers to compare seroconversion rates and post-vaccination HAI titers to calculate the ratio of the geometric mean titers in the two treatment groups. HAI is an in vitro bioassay that determines a subject's serum levels of anti-influenza antibodies. The FDA uses this as a standard immunogenicity assay for licensure. The trial will follow guidelines set out in the FDA guidance document discussing non-inferiority immunogenicity studies. As additional methods to assess immunogenicity, an assessment of anti-NA by performing NA inhibition assays (NAI) and SVN assays will be added. A recent trial supported the use of NAI and SVN assays as a correlate for protection in a trial of geriatric subjects. A healthy human challenge model showed that NAI is more predictive of protection and reduced disease than HAI

In the large HD vaccine clinical efficacy trial (n=31,989) one third of subjects also had immunogenicity data that allowed looking for correlations of immune assays with protection. Their conclusions were that HAI and other immune assays are potential correlates of influenza vaccine protection in older adults, and that the protective thresholds for the HAI assay in the elderly appear consistent with those previously described for younger adults, provided the assay virus matches the circulating virus.

Significance Data compiled by CDC in 2011-2012 showed that there were 1,383,700 residents in NHs. Also about 4,742,500 patients received services from home health agencies, and 1,244,500 patients received services from hospices, collectively accounting for much of the frailest in the US. Overall, these provider sectors served over 8 million people annually (2013). This study will focus on residents in NHs but the findings of this study are highly relevant to persons frail enough to require such services in all of settings where the vast majority are at least 65 years old and thus appropriate for Fluad or HD, influenza vaccines licensed for this age group.

The SD influenza vaccine has diminished efficacy in the older population with the more debilitated LTC residents being among the worst responders yet with the highest mortality. Deaths due to pneumonia and influenza and chronic lung disease were 20 times higher among NH residents compared to community residents. The current availability of two vaccines specifically for the elderly that both appear to work better than SD vaccine begs the question: is the newer and less-costly Fluad vaccine non-inferior or even superior to HD vaccine? The proposed study aims to initially address non-inferiority using immunologic endpoints as this is feasible in the clinical trial R01 grant structure and a critical first step to obtain head-to-head data from the same trial, cohort and vaccine years. This proposed study itself may provide direct guidance on vaccine usage or inform a future trial assessing actual superiority should that be appropriate based on the results of this study.

HD vaccine is increasingly used by older Americans despite its greater cost over the SD vaccine and no preferential recommendation by the Advisory Committee on Immunization Practices (ACIP), the CDC committee responsible for making the vaccine recommendations for the U.S. A finding of non-inferiority in the primary endpoint would provide a strong rationale to consider using Fluad over HD that could result in some cost avoidance across large long-term care system in the U.S. The trial is not powered for a superiority analysis but in a non-inferiority trial if the findings are substantial enough they may show superiority.