Which of the following is an example of a live vaccine?

• A. MMR
• B. Hepatitis B vaccine
• C. Inactivated influenza vaccine
• D. Pneumococcal polysaccharide vaccine

Answer: (A)

Live vaccines use weakened forms of the pathogen that can still replicate to a limited extent, which helps evoke a strong and lasting immune response. The measles, mumps, and rubella (MMR) vaccine fits this, because it contains attenuated versions of the viruses that can replicate enough to stimulate immunity without causing disease in healthy people. In contrast, the hepatitis B vaccine is a recombinant subunit vaccine that delivers a viral protein rather than a live organism; the influenza vaccine listed is inactivated, meaning the virus is killed and cannot replicate; and the pneumococcal polysaccharide vaccine uses purified polysaccharides from the bacteria, with no live microbe involved. So, the best example of a live vaccine is the MMR vaccine.