Clinical Update: The return of influenza season: What has changed?

The 2006-2007 influenza season is upon us. Influenza epidemics have been associated with an average of about 36,000 deaths per year in the United States from 1990 to 1999.¹ In July of this year, the Advisory Committee on Immunization Practices (ACIP) updated its recommendations for the prevention and control of influenza.²

Influenza vaccination continues to be the primary method for the prevention of this illness and its serious complications. In 2006, approximately 218.1 million persons in the United States will be included in one or more of the recommendation's target groups for immunization, summarized in Table 1. The 2006 recommendations include 6 principal changes or updates, summarized in Table 2.

As of July of this year, influenza vaccine manufacturers were projecting that about 100 million doses of influenza vaccine would be available in the United States for the 2006-2007 influenza season, an increase of approximately 16% from last season. The composition of this year's vaccine is based on the influenza A and B viruses that are expected to circulate in the United States during 2006-2007.

Both the inactivated influenza vaccine and the live, attenuated influenza vaccine (LAIV) are available; although each is effective, they differ in several respects.³ The ACIP indicates that although LAIV is more expensive than inactivated influenza vaccine, the price differential between them has decreased for the 2006-2007 season.

Of importance, as of February of this year, 6 states had enacted legislation banning the administration of vaccines that contain mercury. Thimerosal, a mercury-containing compound, is used in multidose vials of inactivated influenza vaccine to reduce the likelihood of bacterial contamination; vaccines that contain trace amounts of thimerosal have less than 1 µg of mercury per dose. Since mid-2001, manufactured vaccines regularly recommended for infants in the United States contain no thimerosal or only trace amounts. These laws may present a barrier to vaccination during this influenza season if the availability of doses of vaccines without thimerosal is inadequate.

Researchers have studied the effects of influenza vaccination on health care costs and productivity losses associated with influenza illness. These studies indicate that influenza vaccination of persons aged 65 years and older in the United States substantially reduces the number of hospitalizations and deaths and contributes to societal costs savings.^4-6 Studies of adults younger than 65 years report that influenza vaccination reduces both direct medical costs and indirect costs from work absenteeism.^7-12

Although vaccination is considered to be the linchpin in the approach to the prevention of influenza, antiviral medications are viewed as an important adjunct to administering the vaccine.¹³ The neuraminidase inhibitors zanam- ivir and oseltamivir have activity against both influenza A and B viruses; both drugs are approved for treatment of uncomplicated influenza virus infections. Oseltamivir is approved for chemoprophylaxis of influenza among persons aged 1 year and older. In March of this year, zanamivir was approved for chemoprophylaxis among children aged 5 years and older.

References:

REFERENCES

1. Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States.

JAMA

. 2003;289:179-186.
2. Centers for Disease Control and Prevention. Prevention and control of influenza. Recommendations of the Advisory Committee on Immunization Practices (ACIP).

MMWR

. 2006;55:1-48.
3. Centers for Disease Control and Prevention, Advisory Committee on Immunization Practices. Vaccines to prevent influenza. February 22, 2006; Resolution No. 2/06-3:1-3.
4. Mullooly JP, Bennett MD, Hornbrook MC, et al. Influenza vaccination programs for elderly persons: cost-effectiveness in a health maintenance organization.

Ann Intern Med.

1994;121:947-952.
5. Nichol KL, Wuorenma J, von Sternberg T. Benefits of influenza vaccination for low-, intermediate-, and high-risk senior citizens.

Arch Intern Med.

1998;158:1769-1776.
6. Riddiough MA, Sisk JE, Bell JC. Influenza vaccination.

JAMA.

1983;249:3189-3195.
7. U.S. Congress. Cost effectiveness of influenza vaccination. Washington, DC: Office of Technology Assessment; 1981.
8. Nichol KL, Lind A, Margolis KL, et al. The effectiveness of vaccination against influenza in healthy, working adults.

N Engl J Med.

1995; 333:889-893.
9. Campbell DS, Rumley MH. Cost-effectiveness of the influenza vaccine in a healthy, working-age population.

J Occup Environ Med.

1997;39:408-414.
10. Bridges CB, Thompson WW, Meltzer MI, et al. Effectiveness and cost-benefit of influenza vaccination of healthy working adults: a randomized controlled trial.

JAMA.

2000; 284:1655-1663.
11. Demicheli V, Jefferson T, Rivetti D, et al. Prevention and early treatment of influenza in healthy adults.

Vaccine.

2000;18:957-1030.
12. Mixeu MA, Vespa GN, Forleo-Neto E, et al. Impact of influenza vaccination on civilian aircrew illness and absenteeism.

Aviat Space Environ Med.

2002;73:876-880.
13. Centers for Disease Control and Prevention. High levels of adamantane resistance among influenza A (H3N2) viruses and interim guidelines for use of antiviral agents--United States, 2005-06 influenza season.

MMWR.

2006;55(Dispatch):1-2.
14. Centers for Disease Control and Prevention. Childhood influenza vaccination coverage--United States, 2003-04 influenza season.

MMWR.

2006;55:100-103.