For a 12-month-old boy exposed to measles, what is the best therapy if he has not been vaccinated?

The best therapy for a 12-month-old boy exposed to measles and who has not been vaccinated is to administer measles immune globulin. This option provides immediate passive immunity to the child, helping to prevent or mitigate the effects of measles infection.

Measles immune globulin contains antibodies that can neutralize the measles virus, thus reducing the severity of the disease in a recently exposed individual, particularly in young children who are at higher risk for complications. It is most effective when given within 72 hours of exposure.

While vaccination with the MMR (mumps, measles, rubella) vaccine is important for future protection, it would not provide immediate protection after exposure and is not considered a form of therapy for someone already exposed. The other options, such as ribavirin and vitamin A, do not directly address the immediate risk of measles infection in this situation. Therefore, the administration of measles immune globulin is the most effective and appropriate therapy following exposure.