Every year the U.S. Centers for Disease Control and Prevention (CDC) selects three strains of the influenza virus in advance to include in that year’s vaccine. If the strains don’t match the ones that eventually circulate, the vaccine is less effective at protecting people. This was the case in the 2007 flu season, and the vaccine had an efficacy of only 40 percent.

This season the vaccine contained three new antigens projected to be good matches for this year’s influenza strain— A/Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and B/Florida/4/2006-like. Also, an all-time high 146 million doses were expected to be available.

Between September 28, 2008 and January 31, 2009, there were low levels of influenza activity, and only three influenza-related infant deaths. There were also low rates of outpatient visits due to influenza-like illnesses (ILI). Data from the U.S. Outpatient ILI Surveillance Network puts the rate at between 0.9 percent and 2.3 percent, which is below the national baseline of 2.4 percent.

Since January influenza activity has increased, which isn’t surprising as flu season usually peaks in February or March. In the latter month the CDC reported that 35 states reported widespread influenza activity. During the second week of March there were seven infant deaths due to influenza, and outpatient visits due to ILI were higher than the national baseline.

Rates of infection could be even lower if vaccination rates were higher. In 2008 the CDC made several recommendations for more effective and widespread vaccination, including:

  • Vaccinating all children between age six months and 18 years. They should be vaccinated as early as September or whenever the 2008-2009 vaccine was ready.
  • Continuing annual vaccination of all children between six months old and four with medical conditions that make them more likely to have complications from the flu.
  • Giving either the trivalent inactive vaccine (TIV, or the shot) or the live-attenuated vaccine (LAIV, or the Flu-Mist intranasal spray) to healthy children and adults from ages two to 49. People with a higher risk for influenza complications such as those with underlying medical conditions, children aged six months to 23 months, and people older than 49 years should receive TIV only.

How Effective are Antiviral Medications (Flu Drugs)?
The CDC also keeps tabs on resistance to licensed antiviral meds such as oseltamivir (Tamiflu™), zanamivir (Relenza™), or adamantanes, such as adamantadine hydrochloride and rimantadine (Flumadine™). The agency reports that between October 1 and Dec 13, 2008, 98 percent of influenza A (H1N1) viruses were resistant to oseltamivir. However, the drug is still effective against influenza A (H3N2) viruses.

Zanamivir remains effective against all the influenza A and influenza B viruses tested. Adamantanes are effective against influenza A (H1N1) viruses, but do little to fight influenza A (H3N2) viruses.

Even though these drugs are popular, vaccination is still the best way to prevent the flu. There are usually only mild symptoms of upper respiratory infection, even in people with respiratory problems or early human immunodeficiency virus (HIV) infection, according to the Cleveland Clinic Journal of Medicine. Also, experts believe the vaccine is responsible for preventing 50 percent of flu-related deaths.

Quick Stats and Facts on Influenza

  • Infants and adults 65 years and older continue to suffer the worse symptoms, with peak rates of pneumonia and influenza hospitalization and death.
  • Vaccination rates have improved, but remain below the Healthy People 2010 initiative’s target of 90 percent for adults age 65 and older, and below 60 percent in people between ages 18 and 64 with high-risk conditions such as pregnancy or working in health care. Vaccination rates for children are even lower.
  • Research studies continue to show that hygienic measures can prevent respiratory viruses from spreading.
  • The World Health Organization and U.S. Food and Drug Administration have recommended the following strains for the 2009-2010 trivalent influenza vaccine: A/Brisbane/59/2007-like (H1N1), A/Brisbane/10/2007-like (H3N2), and B/Brisbane/60/2008-like (B/Victoria lineage) viruses. The influenza B component is the only change from the 2008-2009 vaccine.