Which type of vaccine contains weakened live viruses?

Live attenuated vaccines are designed to contain live viruses that have been weakened through various methods to reduce their virulence while still allowing them to replicate in the body. This replication helps to elicit a strong and durable immune response without causing the disease in healthy individuals. Because the viruses are live, albeit attenuated, they can closely mimic a natural infection, leading to an effective immune response that includes the production of memory cells, which are essential for long-term immunity.

In contrast, toxoid vaccines are made from toxins that have been inactivated, inactivated vaccines use killed pathogens, and subunit vaccines include only parts of the pathogen (like proteins) rather than the whole virus. These approaches differ fundamentally from live attenuated vaccines, as they do not involve the use of live, albeit weakened, viruses.