U.S. scientists hope to have a key ingredient for a swine flu vaccine ready in early May, but tell The Associated Press that the novel virus grows slowly in eggs - the chief way flu vaccines are made.
Even if all goes well, it still will take months before any shots are available for the necessary safety testing in volunteers.
Dr. Jesse Goodman, the Food and Drug Administration's swine flu chief, said Tuesday that scientists are working, in his words, "at 100 miles an hour" to create good raw material to deliver to vaccine manufacturers.
The researchers must engineer a strain that could trigger the immune system without causing illness. At the Centers for Disease Control and Prevention, flu vaccine chief Dr. Ruben Donis says that work is about a third completed.
Meanwhile, health officials said the number of confirmed swine flu cases has jumped to 64 in the U.S.
The Centers for Disease Control and Prevention said Monday that the new count includes "a number of hospitalizations" but they did not say how many. CDC officials had said there had been just one person hospitalized.
The cases are still only in the five states where they previously were reported. There are 17 new cases in New York City, four more in Texas and three additional cases in California.
That brings the total confirmed cases to 45 in New York City, 10 in California, six in Texas, two in Kansas and one in Ohio.
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