It appears likely that there will be a delay and possibly a reduction in the amount of influenza vaccine available for the 2000-2001 influenza season. One possible way of increasing the availability of influenza vaccine for this year is to use a half-dose in healthy adults. The objective of this study is to determine if the immune system responds to a half-dose the same way it responds to a whole dose. This study will use the currently approved inactivated influenza vaccine in healthy adults ages 18 to 49 years old.
If the immune response to the half-dose is not significantly different than the immune response generated to the whole dose, this could be a strategy to extend the amount of vaccine that could be available in this age group.
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Eligible subjects will be randomized to receive a single intramuscular injection of either a half-dose or a whole dose of a currently approved influenza virus vaccine in their arm. Prior to vaccination, subjects will have one tube of blood drawn. Subjects will be given a 3-day diary card to record any symptoms they may experience and asked to return for a second and final visit approximately 21 days following vaccination. A second blood draw will be done.