The Food and Drug Administration has approved 4 vaccines against the H1N1 flu virus (formerly known as swine flu) for 2009. The FDA expects the vaccines to be distributed nationally in October.
Based on preliminary data from adults participating in clinical studies, the 2009 H1N1 vaccines induce a robust immune response in most healthy adults 8 to 10 days after a single dose, as occurs with the seasonal influenza vaccine.
As with the seasonal influenza vaccines, the 2009 H1N1 vaccines are being produced in formulations that contain thimerosal, a mercury-containing preservative, and in formulations that do not contain thimerosal. The FDA said that people with severe or life-threatening allergies to chicken eggs, or to any other substance in the vaccine, shouldn't be vaccinated.