"Attenuated viruses" refers to viruses that have been weakened or modified so that they are less harmful or have reduced effects on the body. Full definition
The MMR vaccine is a mixture of live attenuated viruses, administered via injection for immunization against measles, mumps and rubella. (sciencedaily.com)
The strategy could provide a stealth way to build attenuated viruses for producing vaccines. (sciencemag.org)
The DNA vaccine also is safer because it does not use attenuated viruses to produce viral antigens. (sciencedaily.com)