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Live virus vaccines are designed to elicit an immune response by using weakened forms of the virus, which helps the body build immunity without causing the disease. MMR (Measles, Mumps, and Rubella) and Varicella (chickenpox) vaccines both fall into this category.

The MMR vaccine contains live, attenuated viruses of the three diseases it protects against—measles, mumps, and rubella. Similarly, the Varicella vaccine contains a weakened form of the varicella-zoster virus, which causes chickenpox. By introducing these weakened viruses, these vaccines stimulate the immune system to produce a response, providing long-lasting immunity.

Other options include vaccines that are not live. For instance, DTaP (Diphtheria, Tetanus, and Pertussis) includes components of the bacteria rather than live viruses, and the HPV vaccine primarily uses non-replicating virus-like particles rather than live virus, thus not qualifying as a live virus vaccine. Tdap and influenza vaccines are also inactivated or subunit vaccines rather than being live.

Understanding which vaccines are live viruses is crucial in determining their administration protocols and precautions, especially in populations with compromised immune systems or specific medical conditions