The FDA's vaccine advisory committee meets Monday and almost certainly will accept the WHO recommendation. The CDC's vaccine advisory committee is just as likely to accept the advice in a vote scheduled for Wednesday. The FDA will issue a final ruling in time for vaccine manufacturers to gear up production.
Seasonal flu vaccines usually have three components, and the 2010-2011 vaccine is no exception. Three types of flu bugs circulate in humans: H1N1 and H3N2 type A viruses, and type B viruses.
Scientists take their best guess as to which strains of each type to include. It's not an exact science. In the time it takes to gear up vaccine production, different strains of flu viruses sometimes become dominant.
At this time, the dominant H1N1 strain is definitely the 2009 H1N1 swine flu bug. The dominant H3N2 virus is the so-called Perth strain of the virus, and the dominant B virus is the so-called Brisbane strain.
"Even if [the old] seasonal H1N1 viruses persist, they will not pose a major health risk to people," said WHO flu expert Keiji Fukuda, MD, in a news conference. "The H3N2 and B viruses were persistent through the year, and in some countries we've seen an increase in their activity. We feel these viruses will continue to pose a significant public health risk and recommend they go into the seasonal vaccine for the coming year."
Fukuda said the decision does not mean that the H1N1 pandemic is over. Instead, he suggested, the world is transitioning to a "post-pandemic period" in which there will be flare-ups or even new national outbreaks as the pandemic winds down.
"The ending of a pandemic is not an on-and-off phenomenon," he said. "It does not happen overnight."