In epidemics measles vaccine is to be given within how many days of exposure ?

Ans. is 'a' i.e., 3 days Incubation period of measles virus is 10 days. Incubation period of live attenuated measles virus of live vaccine is 7 days. Thus, if the vaccine is given within 2-3 days of exposure, the replication of vaccine virus takes preference over replication of wild virus. "Susceptible contacts over the age of 9-12 months may be protected against measles with measles vaccine, provided that this is given within 3 days of exposure. This is because, the incubation period of measles induced by vaccine is about 7 days, compaired with 10 days for the naturally acquird measles." -- Park