Flu vaccine less effective in protecting dialysis patients than previously believed

Leah McGrath

Led by Leah McGrath, epidemiology doctoral student, and Alan Brookhart, PhD, associate professor of epidemiology at UNC Gillings School of Global Public Health, the study was published in the April 9 issue of Archives of Internal Medicine.

The study analyzed the effectiveness of vaccination for more than 100,000 Medicare patients with end-stage renal disease in 1997, 1998, 1999 and 2001. The patient population was chosen from the U.S. Renal Data System, a population-based system that collects data on all patients with end-stage renal disease (ESRD) nationwide. Using this information, the research team examined the vaccine’s impact on three outcomes: death from any cause, hospitalizations from flu or pneumonia, or other influenza-like illnesses.

The results revealed the vaccine did not prevent deaths, and it also did not prevent other flu-like illnesses. In addition, the vaccine only prevented 2 percent of flu- and pneumonia-related hospitalizations. These outcomes indicate ESRD patients may benefit less from the flu vaccine than previously thought, said lead study author McGrath.

The team’s findings contradict previous research that the flu vaccine provides 12 percent to 14 percent effectiveness against flu- and pneumonia-related hospitalizations, as well as 25 percent effectiveness against mortality from all causes.

“We want to stress that we don’t recommend stopping vaccination. It’s safe, low risk, and cost effective,” McGrath said. “But the message is that the flu vaccine may not be as effective in the ESRD population as originally thought, and alternative vaccination strategies need to be investigated.”

Although there is no official estimate of the increased risk ESRD patients face from the flu, these individuals typically have other health problems that exacerbate their vulnerability, such as diabetes or cardiovascular illness. Existing research shows that infection in general is the third leading cause of death among this patient population, as well as the second leading cause of hospitalization.

The additional health problems often make it difficult to study the effectiveness of preventive medications and services, said Brookhart. By comparing year-to-year vaccination rates during seasons when the circulating virus matched the vaccine, the research team was able to study vaccine effectiveness in an unbiased way. The vaccine did not match the virus in one year (1997), so the team was able to use patient outcomes that year as a control to which they compared all other years.

McGrath and her colleagues estimated the vaccine effects by comparing outcome rates between different years. Comparisons between 1998 and 1997, as well as between 1999 and 1997, revealed the vaccine provided no benefit against any of the three outcomes. One small benefit emerged when comparing 2001 to 1997 – a 5 percent drop in flu and pneumonia-related hospitalizations.

“We hope these results will be used for discussion among scientists and policy makers to develop better vaccination strategies for high-risk patients,” McGrath said.

Other study authors include Abhijit V. Kshirsagar, MD, MPH, UNC assistant professor of medicine; Stephen R. Cole, PhD, UNC associate professor of epidemiology; Lily Wang, PhD, UNC biostatistics alumna and applications specialist at Cecil G. Sheps Center for Health Services Research; David J. Weber, MD, MPH, professor of epidemiology, medicine and pediatrics; and Til Stürmer, MD, MPH, professor of epidemiology.

The study was funded by an unrestricted fellowship from the UNC-GlaxoSmithKline Center of Excellence in Pharmacoepidemiology and Public Health at the Gillings School of Global Public Health, and is available online. A subscription is required.

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UNC Gillings School of Global Public Health contact: Linda Kastleman, communications editor, (919) 966-8317 or linda_kastleman@unc.edu.