MMR vaccine is a shot that contains weakened (live‑attenuated) viruses for measles, mumps, and rubella. It is given by injection into the muscle. In this study the vaccine was used to see how well it creates long‑lasting protection. Children who received the vaccine early (at 6 months) were compared with children who received a placebo at that time, and later both groups received the routine MMR dose at 4 years of age. The researchers measured the amount of measles antibodies 1‑3 years after the routine dose to determine how strong the immune response was after the early vaccination.

Measles – Measles is a highly contagious viral infection that begins with fever, cough, runny nose, and red eyes. After a few days, a red rash appears, starting on the face and spreading downward. The rash typically lasts about a week. The virus spreads through droplets when an infected person coughs or sneezes. Symptoms may worsen before they improve, and most people recover fully.

Mumps – Mumps is a viral illness that mainly affects the salivary glands, especially the parotid glands near the ears. It starts with fever, headache, and muscle aches, followed by swelling and tenderness of the cheeks. The swelling can last several days to a week. The virus spreads through saliva and respiratory secretions. Most cases resolve as the swelling gradually decreases.

Rubella – Rubella, also known as German measles, is a mild viral infection that starts with low fever, headache, and a pink rash. The rash begins on the face and spreads to the body within a day. Small swollen lymph nodes may appear behind the ears and at the back of the neck. The virus spreads through respiratory droplets. The rash and other symptoms usually disappear within a few days.