The new pandemic H1N1 is causing a "brisk" flu season in the Southern Hemisphere but so far no worse than a moderate influenza pandemic, health officials said on Thursday.
They were speaking to a meeting of U.S. Food and Drug Administration advisers considering the start of human clinical trials of a vaccine against the new swine flu strain, which spread globally in less than two months.
"This is clearly a brisk flu season," Dr. Anthony Fiore of the U.S. Centers for Disease Control and Prevention told the meeting.
H1N1 is the dominant strain, and while it is about as bad as a moderate seasonal flu, it is attacking younger people than seasonal flu usually does. Seasonal influenza kills between 250,000 and 500,000 people globally in an average year.
Global health officials are gearing up to vaccinate against both the seasonal flu, using a traditional cocktail that protects against the three most common strains, as well as against the pandemic H1N1 virus.
Australia's CSL Ltd, Baxter International, GlaxoSmithKline Plc, Novartis AG and Sanofi-Aventis SA all are making H1N1 vaccines and will tell the FDA committee about what they have learned as they work with the virus.
The U.S. National Institutes of Health reported on Wednesday it had assigned human trials of CSL's and Sanofi's vaccines to start in August at various academic centers and clinics. But the FDA must approve these before they can start.
Vaccine experts will test various doses of the H1N1 vaccine to see how large a dose people need to be protected, and also deliver it along with the seasonal flu vaccine to see if that will work.
The CDC's Dr. Nancy Cox said tests had confirmed hat people who have received seasonal flu vaccines in the past have little or no immunity to the new H1N1 virus. The same is true for people in Europe who have received vaccines containing materials called adjuvants, which help boost the immune response to a vaccine.
Cox said CDC tests show the virus can still be treated with Tamiflu and Relenza. Tamiflu, made by Roche AG and Relenza, made by Glaxo, are antivirals that can treat and prevent flu.
Cox also said some experiments suggest the virus has not fully adapted to humans — meaning it still has qualities that make it better suited to infect pigs than people. The CDC is watching to see if it evolves but so far it has not.
The FDA committee will consider letting companies test the adjuvants in the United States in the hope of making limited supplies of the new H1N1 vaccine stretch further.
The CDC has a committee of vaccine advisers meeting next week to recommend who should get an H1N1 vaccine.
