Scanning EM of Influenza Virus From: http://www.cdc.gov/ncidod/diseases/flu/fluvirus.htm

The onset of the influenza season is rapidly approaching and now is the time to start thinking about vaccination. The past several years have seen significant problems with vaccine supplies. The fiscal crisis in Massachusetts and the cutback in state-supplied vaccine will likely make this year challenging as well.

The Centers for Disease Control and Prevention published the Advisory Committee on Immunization Practices (ACIP) recommendations for the Prevention and Control of Influenza for this year in the April 12 edition of MMWR (http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5103a1.htm)¹ Some highlights of the report are as follows:

1. Vaccination rates for high-risk populations are still inadequate.
   

• Vaccination rate among people over age 65 years is approximately 65%. The target for Healthy People 2010 is 90%.
• Vaccination rate for adults aged 18-64 with high risk conditions was 32% in 2000. This is well under the Healthy People 2000 goal of 60%.
• Vaccination rate for children with high-risk conditions is as low as 10% in some studies.
• Vaccination rates in African-Americans and Hispanics continue to be considerably lower than among whites.
  

2. The best time to vaccinate is October-November. However because supplies are uncertain, vaccination efforts should focus on people with high-risk conditions and their household contacts, healthcare workers, and children aged 6 months to less than 9 years receiving the vaccine for the first time and should start as soon as the vaccine is available. Others should be vaccinated as supplies dictate. Vaccination should continue throughout the flu season.
   
   
3. Chemoprophylaxis is not a substitute for vaccination. No effectiveness data are available for chemoprophylaxis in high-risk individuals. In otherwise healthy individuals:

• Rimantadine and amantadine are 70-90% effective in preventing illness from Influenza A.
• Zanamivir and oseltamivir are 84% and 82% effective, respectively, in preventing illness from Influenza A and B.
• All antivirals must be taken daily for as long as there is influenza activity in the local area.
• Rimantadine, amantadine, zanamivir and oseltamivir, when started within 48 hours of onset of symptoms, reduce the duration of symptoms by about 1 day. None of these drugs has been shown to be effective in preventing the serious complications of influenza.

The ACIP report is non-committal concerning the choice of antiviral drugs. A recent report in Annals of Internal Medicine² provides some insight into the best approach. The authors assessed the relative value of 8 treatment strategies for healthy working adults aged 18-50 using combinations of no intervention, vaccination and antiviral strategies. Here are some highlights:

1. All strategies that included vaccination were preferable. Non-vaccination and the use of any antiviral as treatment were of only marginal benefit over no vaccination and no treatment.
2. Vaccination in combination with rimantadine for treatment was the most cost-effective overall strategy. The choice of antivirals was sensitive to the prevalence of influenza B and to the workdays saved. The prevalence of influenza B used in the analysis was assumed to be 16.3%.

Based on the ACIP recommendations and the recent report in Annals:

1. Vaccination is still the best strategy. Adults and children with high-risk conditions should be vaccinated early, with healthy adults to follow.
2. For both treatment and chemoprophylaxis, rimantadine remains the drug of choice for most patients.

The Toll Free Flu Shot Hotline at 1-877-733-3737 provides the latest information about vaccine availability at MGH.

References:

1. MMWR April 12, 2002/51(RRO3);1-31.
2. Lee P, Matchar D, Clements D et al. Economic analysis of influenza vaccination and antiviral treatment for healthy working adults. Ann Intern Med 2002; 137: E225-233.