US Hospitalized Adult Influenza Vaccine Effectiveness Network – Centers for Disease Control and Prevention

The United States Department of Health and Human Services’ Centers for Disease Control and Prevention (CDC) leads national public health efforts and works to protect the health, safety, and security of Americans. To examine how well influenza vaccine prevents hospitalization, the CDC funded the study, US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN).

Results of the project will ultimately help CDC determine the burden of respiratory viruses, which vaccines are best, and where future research efforts need to be prioritized. HAIVEN is a multi-state project; four sites were selected from a national competition to conduct active surveillance during the influenza season: Temple, Texas; Ann Arbor, Michigan; Pittsburgh, Pennsylvania; and Nashville, Tennessee. Patients with acute respiratory infections of less than or equal to 10 days’ duration were eligible for enrollment at hospitals within defined counties.

The Pittsburgh site was granted to the University of Pittsburgh/UPMC. Professor Richard K. Zimmerman, MD, MPH, at the University of Pittsburgh and the PittVax team, a research group based in the Department of Family Medicine, used hospitalization data from the Pennsylvania Health Care Cost Containment Council (PHC4) for the HAIVEN project. In particular, Dr. Zimmerman is studying the burden of various respiratory viruses in Allegheny County that lead to hospitalizations. As part of this work, PHC4 data provided market share as well as burden estimates of acute respiratory illness to define population-based estimates.

In analyzing data, Dr. Zimmerman noted that seasonal patterns for influenza and respiratory syncytial virus (RSV) were apparent, and quite a bit of variance in the virus was found from year-to-year. He noted that these findings are likely due to characteristics of the virus, with some viruses being more infectious, as well as to characteristics of immunity in the population. When there is little immunity to a particular virus in the population, it can spread widely.

Because of variations in population immunity and changes in the viruses over time, a variation of a case control study called a test negative design is used for determining the effectiveness of vaccines and predicting the next one. Dr. Zimmerman described, “In the test negative design, cases and controls both come from a population that seeks healthcare for acute respiratory illness. This limits biases. The World Health Organization (WHO), Food and Drug Administration (FDA) and CDC determine the next influenza vaccine strains by looking at the worldwide epidemiology of the strains, which viruses are changing and for which viruses they have a vaccine candidate that can produce immunity and has good growth characteristics for the manufacturing facilities.”

Dr. Zimmerman explained further, “Most influenza vaccines use the same basic manufacturing process for the different strains. However, newer vaccines have different manufacturing processes or different additives, called adjuvants, to boost immunity.”

In addressing the value of PHC4 data, Dr. Zimmerman noted that the market share and population-based data provided by PHC4 were very useful and valuable to the HAIVEN project and to studies of the burden of respiratory viral illness.

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