Why babies under 6 months cannot get the measles vaccine
The MMR (measles, mumps, rubella) vaccine is not licensed for babies younger than 6 months. Their immune systems are still developing, and the vaccine does not work well at this age. The earliest a baby can receive MMR is 6 months and only in special situations such as a measles outbreak or international travel.
How your baby is protected at birth
During pregnancy, antibodies (infection-fighting proteins) pass from the mother to the baby through the placenta. These antibodies can help protect newborns from measles in the first weeks to months of life.
However, this protection fades quickly:
– Most babies lose protective antibody levels by 3 months of age.
– By 6 months, nearly all babies no longer have enough antibodies to fight measles.
What you can do to protect your baby
Since babies under 6 months cannot be vaccinated, protection depends on the people and environment around them:
1. Make sure everyone around your baby is vaccinated. All household members, caregivers, and close contacts should be up to date on their MMR vaccine. This creates a “shield” of immunity around your baby (sometimes called “cocooning”).
2. Avoid high-risk settings during outbreaks. If measles is circulating in your community or you are aware of local cases, avoid crowded indoor spaces (airports, waiting rooms, large gatherings) with your baby when possible.
3. Do not travel internationally with an unvaccinated infant if possible. If travel is unavoidable and your baby is 6 months or older, talk to your pediatrician about getting an early MMR dose before departure. Babies under 6 months cannot receive this dose.
4. Breastfeed if you are able. Breast milk contains antibodies (especially IgA) that may offer some additional, modest protection against infections, including measles. Breastfeeding is not a substitute for vaccination but may provide a small extra layer of defense.
5. Know your own immunity status. If you are unsure whether you were vaccinated or had measles, ask your doctor about checking your immunity with a blood test (measles IgG). If you are not immune and not currently pregnant, getting vaccinated protects both you and your baby.
What to do if your baby is exposed to measles
If your baby under 6 months has been in contact with someone who has measles:
– Seek medical care immediately. Call your pediatrician or go to the emergency department right away. Let them know about the measles exposure before arriving so the office can take precautions.
– MMR vaccine is NOT an option for babies under 6 months, even after an exposure. Immune globulin is the only post-exposure treatment available for this age group. Immune globulin works best when given as soon as possible, ideally within 72 hours and no later than 6 days after exposure. It can prevent or reduce the severity of measles.
Warning signs of measles in babies
Measles can be very serious in young infants. Contact your doctor immediately if your baby develops any of the following, especially after a known exposure:
– High fever (often 104°F / 40°C or higher)
– Cough, runny nose, or red/watery eyes
– A rash that starts on the face and spreads downward to the body
– Unusual fussiness, poor feeding, or extreme sleepiness
Babies under 1 year are at the highest risk for serious complications from measles, including pneumonia, brain swelling (encephalitis), and hospitalization.
Key takeaways
– Babies under 6 months cannot receive the measles vaccine.
– Maternal antibodies provide some early protection, but this fades by 3–6 months.
– The best way to protect your baby is to ensure everyone around them is vaccinated.
– If your baby is exposed to measles, seek medical care immediately — immune globulin can help if given promptly.
– Talk to your pediatrician about any concerns, especially if there is a measles outbreak in your area or you are planning travel.