U.S. Influenza Statistics and What to Expect

Almost all the influenza currently circulating is the new pandemic strain and, as a result, the seasonal influenza vaccine has so far had little use. The pandemic vaccine has just now begun to be distributed and given to patients. We are still in the heart of the flu season. It is too early to tell from the data if the country itself has peaked in terms of the number of cases. There are also regional and local differences – some areas have already been hit hard, as evidenced by school closures. Other areas have not yet peaked. It is also too early to tell if the pandemic vaccine has made any difference in the overall numbers.

In usual influenza seasons, an estimated 36,000 deaths occur directly or indirectly from influenza in the U.S., with 90% of these in the elderly or in those with weakened immune systems. The good news this season is that the elderly seem to have some immunity to the pandemic H1N1 strain, probably due to different H1N1 strains that were in circulation until the 1957 H2N2 pandemic, at which time H2N2 replaced H1N1 as the seasonal strain. So, we are seeing far fewer total deaths, just over 1,000 (but perhaps as high as 3,000, according to other CDC data not currently publicized) since the pandemic started.

The bad news is that we are seeing more than the usual number of deaths in younger people (under age 65). People with weakened immune systems are still dying disproportionately, and we are seeing more than the usual number of deaths in previously healthy individuals including children and pregnant women.

Between vaccine being distributed / administered and the pandemic running its course through communities, one would hope to see a downward trend in hospitalizations and deaths. The vast majority of unvaccinated patients who get pandemic influenza will be fine after a few days of misery. Similarly, patients who get the vaccine prior to getting sick from pandemic influenza will not have a serious reaction to the vaccine and also will not get ill or die from the virus.

Next year’s seasonal influenza vaccine will include the current pandemic H1N1 strain (or a mutated version), and influenza B. It can be expected that subsequent seasons will be mild because so many will have already gotten ill and developed immunity to the novel H1N1. The elderly will continue to have some natural immunity, and the vaccine and herd immunity will protect most of the rest of the population.
(from Extreme Thinkover by Dr. John Bogen, MD November 8, 2009)