Correct option is A
Some types of COVID-19 vaccines work by introducing a live attenuated version of the SARS-CoV-2 virus. A live attenuated virus is a weakened form of the virus that cannot cause illness but still stimulates the immune system to recognize the virus and produce a strong immune response. Examples of vaccines that use live attenuated viruses include traditional vaccines like those for measles, mumps, and rubella (MMR). This method is different from mRNA-based vaccines that use a harmless piece of the virus, such as the spike protein.
