What does the MMR vaccine protect against?

The MMR vaccine is specifically designed to protect against three infectious diseases: measles, mumps, and rubella. These diseases are highly contagious and can lead to serious complications. Measles can cause severe respiratory issues and complications such as encephalitis. Mumps primarily affects the salivary glands but can also lead to complications like meningitis or orchitis. Rubella, while often mild in children, poses significant risks during pregnancy, including congenital rubella syndrome, which can result in serious birth defects.

The other choices mention diseases that are not covered by the MMR vaccine. For instance, varicella refers to chickenpox, which is vaccinated against using a different vaccine. Pneumonia is often caused by various bacteria and viruses, and while it can be associated with other infections like measles, it is not directly targeted by the MMR vaccine. Influenza is seasonal and also has its own specific vaccine. Thus, the correct choice accurately reflects the diseases that the MMR vaccine is intended to prevent.