Dr. Greene's Answer
Almost all adults are susceptible to pertussis, or whooping cough. Between 60 and 80 percent of infants are protected after the first 3 doses of vaccine, but this protection begins to disappear when they are toddlers. After the 4th immunization at 18 months old, 80 percent are protected for the next 3 to 4 years. The 5th dose, at kindergarten entry, protects them for another few years. A booster vaccine is given to adolescents at 11 years of age or above.
People who have been exposed to probable or confirmed pertussis should either receive a course of preventative antibiotics (and I say this as someone strongly opposed to the overuse of antibiotics), or be kept home from daycare, school, or work for at least 2 to 3 weeks.
Children under age 7 who have been exposed should receive a pertussis vaccine, unless they have already had 4 doses of pertussis vaccine (and the last dose within 3 years), or unless there is a compelling reason not to immunize them.