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

Ans. is 'c' i.e., 7 days o Normally the incubation period of measles is 10 days from exposure to appearance of first symptom (fever). o But, when infection is induced aificially by injecting the live measles vaccine, the incubation period is somewhat shoened, averaging 7 days. Why is it so ? Lets see o In natural infection, virus enters through respiratory tract and then it gains entry to blood stream. o In contrast, measles vaccine is injected subcutaneously it immediatly enters into circulation. So, measles vaccine has incubation period less (3 days) than natural infection. o For this reason, measles vaccine should be given within 2-3 days after exposure, so that vaccine virus can induce immunity before the natural virus can cause clinical illness.