Each year the US government has guessed which strains were most likely to spread. They seem to always guess right - don't they? This flu season, the government protected people with a trivalent vaccine that included the A/Beijing/262/95-like (H1N1) and the A/Sydney/5/97-like (H3N2). It also contained the B/Beijing/184/93-like hemagglutinin antigens. For those not familiar with virology, the H and N refer to proteins on the outside of the virus, the hemagglutinin and neuraminidase, which are responsible for the virus attaching to, and then invading, a host cell. The public has been quite pleased with the success of the vaccines offered so far. But that will change in the future.
Researchers at the US Army Medical Research Institute of Infectious Diseases (or USAMRIID) at Fort Detrick in Frederick MD have reconstructed and modified the H1N1 Spanish Flu virus, making it far more deadly than it ever was back when it was responsible for the 1918-1919 flu pandemic that killed over 20 million worldwide and over 500,000 here in the US. Consider that it could have killed many more, but back then, people couldn't hop on a jet and travel from New York to L.A. in five hours. Now, our ability to travel will increase the spread and will be our downfall.
The flu vaccines contain killed virus and protect the body well against challenge by that particular strain, but work poorly against other strains not included in the inoculation. At some point, the vaccine stockpile will include the more lethal modification of the 1918 H1N1 in its live form. Most people receiving this vaccine will simply be renewing their annual flu shot, and the vaccine will still include the inactivated version of the more benign form of H1N1 (as was included in this year's vaccine). The presence of the milder strain in the inoculum will slow down the progression of the more lethal H1N1 form, so people will become sick more slowly - but they will still eventually die. It will just take a few weeks longer.