Measles vaccine given to contact of measles case exces protective effect within-

- susceptible host of measles 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 , compared with 10 days for naturally acquired measles. Thus protective effect is obtained within 7 days. Reference : Park's textbook of preventive and social medicine, 23rd edition, pg no:149