Antigenic shift

The two words "antigenic shift" strike fear in the minds of immunologists and epidemiologists. According to the National Institute of Health (NIH):

http://www3.niaid.nih.gov/topics/Flu/Research/basic/AntigenicShiftIllustration.htm
"The genetic change that enables a flu strain to jump from one animal species to another, including humans, is called antigenic shift."

When the mutation occurs, a more more lethal strain can develop. Today's article exposes this is already happening:

http://www.express.co.uk/posts/view/123818/New-swine-flu-mutation-far-more-deadly-

Let's hope the vaccines and anti-virals remain effective against mutated strains.

Mortality rates from swine flu

The FDA Vaccine Advisory Committee had a meeting yesterday, and according to the latest data, 5 - 9% of confirmed H1N1 cases required hospitalization, with approximately half of them dying. That equates to a 2.5 - 4.5% lethal rate.

In Mexico, 6% of confirmed cases required hospitalization, and 46% died, which yields a 3% lethal rate, in line with US data.

http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterials/BloodVaccinesandOtherBiologics/VaccinesandRelatedBiologicalProductsAdvisoryCommittee/UCM172424.pdf

According to the CDC:

Each flu season is unique, but it is estimated that, on average, approximately 5% to 20% of U.S. residents get the flu, and more than 200,000 persons are hospitalized for flu-related complications each year. About 36,000 Americans die on average per year from the complications of flu

.

Extrapolating those numbers, 15 million to 60 million Americans contract the seasonal flu every year. Of those, 1.3% to 0.3% require hospitalization. Of those hospitalized, 18% will die, on average. The lethal rate is 0.24% to 0.06%.

By contrast, with the swine flu, based on a worst-case scenario of 100 million Americans (33%) contracting the swine flu, up to 9 million will require hospitalization, of which 4.5 million will perish. That's a 125-fold increase in deaths from the swine flu this winter season.

We won't know what the actual outcome will be yet, but the consensus among world health officials is that this novel H1N1 virus is spreading faster than any other pandemic influenza in history. While not especially lethal, it is more lethal than most seasonal influenza viruses.