<qa>  What is the blood sample drawn before and on several occasions after each vaccination?A blood sample is drawn before and on several occasions after each vaccination to check the subjects health and to evaluate the immune response to the vaccine. At 1, 3, 7, 14, and 21 days after each vaccination, participants come to the clinic for a check of vital signs temperature, pulse, respiration, and blood pressure, brief physical examination, and history of symptoms since the previous visit. 