May 6, 2009 -- If there's an H1N1 swine flu pandemic, vaccine makers should be able to churn out "at least" 1 billion to 2 billion doses of H1N1 swine flu vaccine, the World Health Organization (WHO) estimates.
The WHO hasn't yet declared an official pandemic. But given the growing number of cases worldwide -- as of Wednesday, 1,658 confirmed cases in 23 nations -- acting CDC Director Richard Besser, MD, says it would be surprising if an official pandemic was not eventually announced.
If that happens, world vaccine production would lag only four to six months behind, says Marie-Paule Kieny, PhD, the World Health Organization director of the Initiative for Vaccine Research.
"The current world capacity to make seasonal influenza vaccine is around 900 million doses per year," Kieny said today at a news conference. "This would translate to 1 billion to 2 billion doses of H1N1 vaccine if there should be a pandemic."
The decision whether to ask vaccine manufacturers to go full speed ahead with making an H1N1 swine flu vaccine may be made on Thursday at a WHO advisory committee meeting. The committee is charged with advising the WHO secretary-general to make a formal request to manufacturers.
Besser said the CDC has not yet decided whether to ask manufacturers for a swine flu vaccine, although early vaccine preparations are under way.
Many obstacles to a vaccine remain:
• It's not yet known how well the H1N1 virus will grow in eggs.
• There's no way to know for sure that vaccines against the current H1N1 virus strain will match the virus spreading six months from now.
• It's not clear how many vaccine doses will be needed for immunity. If people already have some immunity from immunization or prior infection with seasonal H1N1 flu bugs, only one dose may be needed. If not, two doses may be required.
• It's not known how big a dose of vaccine will be needed. If big doses are needed, there will be fewer doses to go around.
• Any new vaccine will have to clear at least preliminary safety tests.
Next week, Kieny said, the WHO will meet with vaccine makers to discuss how to make sure poorer nations have access to H1N1 swine flu vaccine.
"We are appealing to corporate responsibility and working together toward equitable access," she said. "The manufacturers we have discussed this with have been very forthcoming, and we hope in the coming weeks to announce some agreement has been signed."
Meanwhile, Besser urged Americans to stay on the alert.
"This remains a dynamic situation," he said at today's news conference. "We remain concerned. We see continued spread around the country."
As state health departments receive test kits from CDC, they are working through their backlog of suspected cases. The result is that case numbers have surged a bit. But Besser noted that new cases of H1N1 swine flu continue to occur, and that more severe cases and deaths can be expected.
As of today, there were 1,487 probable and confirmed cases in 44 states. The ages of the patients in these cases range from 3 months to 81 years, but the median age is 16. It's still not clear why older children and young adults are more likely to get the new flu.