Measles

Measles is an extremely contagious viral illness that spreads through the air when an infected person breathes, coughs, or sneezes. The best way to protect yourself and your family against measles is the safe and effective MMR vaccine.

Content written by Joanne E. McGovern, Lecturer in Medical and Public Health Disaster Planning and Operations, and Michael Cappello, MD, Department Chair and Professor of Epidemiology (Microbial Diseases).

Published: August 2025

What are the symptoms of measles?

• Starts with a high fever, along with a cough, runny nose, and irritated, watery eyes.
• Followed by a red, blotchy rash that begins on the face and spreads downward.
• Small white spots (called Koplik spots) may appear inside the mouth before the rash emerges.

2 hours

The time the measles virus can linger in the air after an infected person leaves a room.

9 in 10

The number of people without immunity who will get infected if exposed.

• It may lead to a rare but fatal condition called Subacute Sclerosing Panencephalitis (SSPE), developing years after infection.
• The virus can also suppress the immune system, leaving individuals more susceptible to other illnesses and infections.

Can measles be prevented?

Absolutely. The MMR vaccine (measles, mumps, and rubella) is highly effective—two doses protect about 97% of people, which significantly reduces the risk of spread to others in the community who may not be eligible to receive the vaccine.

Is the MMR vaccine safe?

Yes, for almost everyone. The risks from the disease far outweigh the minimal risks associated with vaccination. Like any other medicine, it can have side effects like a sore arm, fever, mild rash, or temporary joint pain. In decades of global use, the MMR vaccine has been linked with a very small risk of febrile seizures, which are not associated with any long-term effects. Serious allergic reactions are extremely rare, but people allergic to any component of the vaccine should not get it.

Do I need to get (re)vaccinated against measles?

*People with HIV who were vaccinated before the establishment of effective antiretroviral therapy and do not have evidence of current severe immunosuppression should be revaccinated.

**People who should not receive the MMR vaccine include people who have had a severe allergic reaction after a previous dose, have an allergy to a vaccine component, have severe immunodeficiency, or are pregnant.

SOURCES: CDC, ACIP, Yale Medicine, MSN, Johns Hopkins, YALE ESF-8 Virtual Medical Operation Center