When the disease is introduced into isolated communities where it has not been endemic, all age groups develop clinical measles. A classic example of this was the introduction of measles into the Faroe Islands in 1846; only people over age 60 years, who had been alive during the last epidemic, escaped the disease. In places where the disease strikes rarely, its consequences are often disastrous, and the mortality rate may be as high as 25%. The highest incidence of measles is in the late winter and spring. Infection is contracted by inhalation of droplets expelled in sneezing or coughing. Measles is spread chiefly by children during the catarrhal pro-dromal period; they are infectious from 1-2 days prior to the onset of symptoms until a few days after the rash has appeared.
Live attenuated measles virus vaccine effectively prevents measles. About 95% of children properly inoculated with live virus vaccine develop antibodies that persist for at least 14 years.
Less attenuated vaccine virus may produce fever and a modified skin rash in a proportion of vaccines, this reaction can be prevented by the simultaneous administration of gamma globulin (0.02 mL/kg body weight) at a separate site from the vaccine. The more attenuated vaccine viruses do not produce symptoms and do not require the use of gamma globulin. The different vaccine viruses appear to be equally effective in producing immunity.
Measles antibodies cross the placenta and protect the infant during the first 6-10 months of life. Vaccination with then live virus fails to take during this period, and measles immunization should be deferred until 15 months of age. This applies both to monova-lent measles vaccine and to combined measles-mumps-rubella vaccine.
When the live vaccine was first introduced, it was often given to infants in the first year of life. This did not produce immunity, and such children must be revaccinated. Vaccination is not recommended in persons with febrile illness or allergies to eggs or other products used in the production of the vaccine, and in persons with immune defects. Epidemiologic studies have shown that the risk, if any, of SSPE occurring in vaccinated persons is much less than the risk of its occurring in persons who have natural measles.
Killed measles vaccine should be discouraged, this is due to the fact that some vaccines become sensitized and develop either local reactions when revaccinated with live attenuated virus or sever atypical measles when infected with wild virus or even with live vaccine virus. Measles may be prevented or modified by administering antibody early in the incubation period. Human gamma globulin contains antibody liters of 200-1000 against 100 TCIDs of virus. With small doses, the disease can be made mild and immunity ensues. With a large dose of gamma globulin, the disease can be prevented; however, the person remains susceptible to infection at a later date. Antibodies given later than 6 days after exposure are not likely to influence the course of the disease.