"There's been a lot of debate about optimal treatment strategies," Lee said. "Our study shows that society as a whole benefits if you vaccinate the entire population and use antiviral medications on those who get sick."
Influenza, a viral disease characterized by nasal congestion, dry cough and fever, affects 10 percent to 20 percent of the U.S. population each year, with an average of 2.8 work days lost per ill individual. Although anyone can get a flu shot, the Centers for Disease Control recommend vaccination only for specific groups, including the elderly, those with weakened immune systems and health-care workers. Most healthy adults choose not to get flu shots.
In the study, published in the Aug. 20 issue of the journal Annals of Internal Medicine, Lee and colleagues gathered previously published data on the costs and benefits of flu vaccination and treatment of flu patients with antiviral medication in healthy adults ages 18 to 50. These included costs of the vaccine and drugs, lost work time due to illness and duration of symptom relief from antiviral medications. They also surveyed 210 patients at a family practice clinic about their willingness to pay for flu symptom relief and medication without side effects.
The researchers entered this information into a computer model that subtracted the costs from the benefits to yield a net benefit or cost. They ran the model 1,000 times while systematically changing the data within known limits. For example, the cost of the flu vaccine averages $10.41 but may range from $5 to $20. For each combination of costs and benefits, the computer determined which of eight prevention and treatment strategies was most cost beneficial. The strategies included either vaccination or non-vaccination and, for those who became ill, treatment with one of three antiviral medications, including rimantadine, zanamivir and oseltamivir, or no treatment.
Using the average values for all costs and benefits, the researchers found that the four strategies that included vaccination had an overall savings of about $30 each compared to no vaccination and no treatment with antivirals. Treatment with rimantidine or zanamavir without vaccination had small savings (less than $5); treatment with oseltamivir without vaccination had a cost of 3 cents.
Lee said using a computer model may appear less rigorous because randomized clinical trials are usually the gold standard of medical research. But two previous clinical trials on the costs and benefits of flu vaccinations for healthy adults yielded widely different results. One found a savings of $46.85 per vaccination, while another found costs of $65.59 and $11.17 per vaccination over two seasons.
"Clinical trials are snapshots in time. They look at one flu season and one flu vaccine," Lee said. "In a clinical scenario where variables change over time, randomized clinical trials are not the best way to answer questions."
Using their computer model, Lee and colleagues found that a strategy that included vaccination was optimally cost-beneficial in 95 percent of their 1,000 runs. Non-vaccination became optimal when the probability of contracting the flu was less than 6.3 percent - a very mild flu season.
The study also found that treatment of flu patients with antiviral medications was optimal in 85 percent of the runs. Surprisingly, the older antiviral rimantidine was as effective as the newer drugs zanamivir and oseltamivir. But no drug emerged as a clear winner; the medications need to be compared in head-to-head tests, Lee said.
All three antiviral medications are readily available, but the United States has experienced shortages of the flu vaccine in recent years. The prevalence of different flu strains changes over time, so the two main pharmaceutical companies that manufacture the vaccine make new batches each year based on World Health Organization recommendations. In 2001, fewer than 90 million doses were available in the United States, and shipment of the vaccine to clinics was delayed.
"For most flu seasons, it is cost-beneficial for the whole society to be vaccinated. But, if there's not enough vaccine to go around, you need to vaccinate those who need it most first," Lee said.
Stanford University Medical Center integrates research, medical education and patient care at its three institutions - Stanford University School of Medicine, Stanford Hospital & Clinics and Lucile Packard Children's Hospital at Stanford. For more information, please visit the Web site of the medical center's Office of Communication & Public Affairs at http://mednews.