Which vaccines contain live attenuated viruses?

• A. Influenza nasal spray, MMR, and Varicella
• B. Inactivated influenza shot, Hep B, Polio
• C. DTaP, Hib, PCV
• D. Rotavirus vaccine only

Answer: (A)

Live attenuated vaccines use weakened forms of viruses that can still replicate in the body, which often provokes a strong, lasting immune response similar to a natural infection. The influenza nasal spray contains a live, attenuated influenza virus. The MMR vaccine is made from live attenuated measles, mumps, and rubella viruses. The Varicella vaccine uses a live attenuated varicella-zoster virus. Because these vaccines replicate to some degree in the host, they tend to produce robust immunity after fewer doses.

Inactivated or non-live vaccines in the other options—such as the inactivated influenza shot, Hepatitis B, and polio vaccines in that set, as well as DTaP, Hib, and PCV—do not contain live viruses and rely on other forms of immune stimulation. Rotavirus vaccines are also live attenuated, but they are not part of this particular grouping.