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

• A. DTap vaccine
• B. MMR
• C. Hepatitis B vaccine
• D. Oral polio vaccine (live)

Answer: (B)

Live attenuated vaccines use weakened forms of real pathogens that can still replicate in the body, enough to mimic a natural infection and provoke a strong, lasting immune response. Because they resemble the way the body would respond to a true infection, they typically induce robust humoral and cellular immunity and often require fewer doses.

Measles, mumps, and rubella in a single vaccine contain attenuated viruses that replicate briefly in the vaccinated person, generating durable immunity with strong protection. That’s why this vaccine is the classic example of a live attenuated option. Other items on the list are not live attenuated: some are inactivated or subunit vaccines, which do not replicate, and thus generally produce a different immune profile. (It’s also worth noting that another example of a live attenuated vaccine is the oral polio vaccine, though its use varies by region.)