Complete the Words

Vaccines protect people by teaching the immune system to recognize a germ before a real infection happens. Most vaccines (1)con____ a (2)weak____ or (3)harm____ (4)pa__ of a (5)vi___ or bacterium, which the (6)bo__ (7)tre___ as a (8)thr___ and (9)lea___ to (10)att___. If the real germ appears later, special memory cells recognize it at once, and the body can fight it off quickly, often before the person even feels sick. Some vaccines need booster doses because this protection slowly fades over the years.