Live attenuated vaccine:

Answer: A. Measles. (Ref Park's Textbook of PSM 22nd/Pg.99)Answer is measles not typhoid as typhoid may be inactivated also but measles is always live attenuated.LIVE VACCINES (e.g., BCG, measles, oral polio etc.)Live vaccines are prepared from live (generally attenuated) organisms. These organisms have been passed repeatedly in the laboratory in tissue culture or chick embryos and have lost their capacity to induce full blown disease but retain their immunogenicity.In general, live vaccines are more potent immunizing agents than killed vaccines, reasons being:(i) live organisms multiply in the host and the resulting antigenic dose is larger than what is injected,(ii) live vaccines have all the major and minor antigenic components,(iii) live vaccines engage certain tissues of the body, as for example, intestinal mucosa by the oral polio vaccine# When two live vaccines are required they should be given either simultaneously at different sites or with an interval of at least 3 weeks.# In the case of live vaccines, immunization is generally achieved with a single dose.# The exception is polio vaccine which needs three or more doses to be given at spaced intervals to produce effective immunity.# Live vaccines usually produce a durable immunity, but not always as long as that of the natural infection.# Live vaccines must be properly stored to retain effectiveness.# Serious failures of measles and polio immunization have resulted from inadequate refrigeration prior to use.