An influenza pandemic has the potential to cause widespread illness and death, is very costly, and strains the health care system's capacity to respond. The widespread outbreak of the 2009 H1N1 influenza virus in the summer and fall of 2009 highlighted the urgent need to identify effective prevention and mitigation strategies for an influenza pandemic. Researchers led by Nayer Khazeni, M.D., M.S., of Stanford University Medical Center, conducted two studies designed to identify the most effective and cost-effective strategies for dealing with an influenza pandemic. The first study focused on different 2009 H1N1 vaccination strategies, and the second study assessed influenza A (H5N1) mitigation and response strategies. The two studies described here were supported in part by the Agency for Healthcare Research and Quality (HS18003).
Khazeni, N. K., Hutton, D. W., Garber, A. M., and others (2009, December). "Effectiveness and cost-effectiveness of vaccination against pandemic influenza (H1N1) 2009." Annals of Internal Medicine 151, pp. 829-839.
The researchers developed a model of progression of the 2009 H1N1 virus to determine how vaccination at one of two points in time would affect the course of the pandemic. They followed a hypothetical group of 8.3 million individuals living in a large U.S. city and ranging in age from 0 to 100 years with an average remaining life expectancy similar to the population of New York City.
The researchers compared the effectiveness and cost-effectiveness of no vaccination, vaccination in mid-October, and vaccination in mid-November. They found that vaccinating 40 percent of the population in October would slow widespread transmission of the virus and be cost-saving, adding 69,679 quality-adjusted life years (QALYs) and saving $469 million relative to no vaccination. Vaccinating 40 percent of the population in November would add 49,422 QALYs and save $302 million relative to no vaccination. Regardless of the timing of vaccination, complete coverage of the population is not necessary to shorten the pandemic, note the researchers. They also point out that highly effective nonpharmaceutical interventions—such as early use of hand washing and surgical masks—could significantly delay the peak of the pandemic, increasing the effectiveness and cost-effectiveness of delayed vaccination.
Khazeni, N., Hutton, D. W., Garber, A. M., and others (2009, December). "Effectiveness and cost-effectiveness of expanded antiviral prophylaxis and adjuvanted vaccination strategies for an influenza A (H5N1) pandemic." Annals of Internal Medicine 151, pp. 840-853.
The influenza A (H5N1) virus is one of the most important international public health concerns of the 21st century due to its potential to cause a pandemic, note these researchers. To have pandemic potential, a virus must meet three criteria: high virulence, antigenic uniqueness, and sustained human-to-human transmissibility. The H5N1 virus meets two of these criteria. It does not yet have the ability for sustained spread among humans, although it could develop this ability through spontaneous mutation or an interspecies link (such as swine).
To estimate the effectiveness and cost-effectiveness of alternate pandemic H5N1 mitigation and response strategies, the researchers examined three scenarios: vaccination and antiviral medication in quantities similar to those available in the U.S. stockpile (stockpile strategy), stockpile strategy but with expanded distribution of antiviral agents (expanded prophylaxis strategy), and stockpile strategy but with adjuvanted vaccine (expanded vaccination strategy). An adjuvant is a substance added to a vaccine to improve the immune response so that less vaccine is needed. Expanded vaccination was the most effective and cost-effective of the three strategies examined, averting 68 percent of infections and deaths and gaining 404,030 QALYs at $10,844 per QALY gained relative to the stockpile strategy. The researchers were encouraged by the finding that the expanded vaccination strategy resulted in increased effectiveness and population coverage, because it demonstrates that the ongoing commitment to increase stockpiles of adjuvant can substantially reduce the morbidity and mortality of a severe influenza pandemic.