Is the measles‑mumps‑rubella (MMR) vaccine contraindicated in pregnancy, and what should be done if a pregnant woman is inadvertently vaccinated or exposed to measles, mumps, or rubella?

MMR Vaccine is Absolutely Contraindicated During Pregnancy

The MMR vaccine must never be administered to pregnant women due to the theoretical risk of fetal infection from live attenuated viruses, though inadvertent vaccination is not an indication for pregnancy termination. 1, 2

Contraindication and Rationale

• MMR vaccine contains live attenuated measles, mumps, and rubella viruses and is absolutely contraindicated during pregnancy. 1, 2
• The contraindication is based on theoretical concerns that live virus could cross the placenta and infect the fetus, though actual documented harm is extraordinarily rare. 2, 3
• Mumps vaccine virus has been shown to infect the placenta and fetus, but there is no evidence it causes congenital malformations in humans. 2, 1

What to Do If Inadvertent Vaccination Occurs

If a woman is inadvertently vaccinated during pregnancy, reassure her that this is not ordinarily a reason to consider pregnancy termination. 2, 1

Reassuring Safety Data

• Among 321 rubella-susceptible pregnant women vaccinated within 3 months of conception, zero infants had malformations compatible with congenital rubella syndrome. 2, 3
• The estimated risk for serious malformations from RA 27/3 rubella vaccine (the strain used in the United States) ranges from 0% to 1.6%, substantially less than the ≥20% risk from wild-type rubella infection in the first trimester. 2
• Post-marketing surveillance of 425 prospectively followed pregnancies where women received MMR within 30 days before conception through the second trimester showed no abnormalities compatible with congenital rubella syndrome. 1

Important Exception

• One case of congenital rubella syndrome has been documented following inadvertent MMR vaccination at 5 weeks gestation, though the vaccine manufacturer was unknown. 1, 4
• This single case among hundreds of thousands of exposures underscores that while the risk is not zero, it remains extremely low. 4

Pre-Pregnancy Vaccination Strategy

All women of childbearing age without documented immunity should receive MMR vaccine before conception. 5

• Acceptable evidence of immunity includes documented prior MMR vaccination or serologic confirmation of rubella immunity. 6, 5
• Women must avoid pregnancy for 3 months (or 28 days per most recent guidance) after MMR vaccination. 5, 3
• Target vaccination during routine medical visits, gynecologic visits, family planning encounters, or premarital evaluations. 5

High-Risk Populations Requiring Special Attention

• Women born outside the United States, particularly those of Hispanic ethnicity, require targeted outreach as recent rubella outbreaks have occurred in these populations who may lack routine childhood vaccination. 5

Management of Measles Exposure During Pregnancy

If a pregnant woman without measles immunity is exposed to measles, administer immune globulin (IG) 0.25 mL/kg intramuscularly (maximum 15 mL) immediately if exposure occurred within the past 6 days. 6

Critical Distinction

• Never administer MMR vaccine to a pregnant woman for post-exposure prophylaxis, even within 72 hours of exposure—IG is the only option. 6
• While MMR would be preferred post-exposure prophylaxis for non-pregnant individuals within 72 hours, pregnancy is an absolute contraindication. 6
• Monitor for measles symptoms (fever, cough, coryza, conjunctivitis, followed by maculopapular rash) for 21 days after exposure. 6

Postpartum Vaccination Protocol

All non-immune postpartum women should receive MMR vaccine before hospital discharge, regardless of breastfeeding status. 6, 5

• Immediate postpartum vaccination could prevent approximately 40-50% of future congenital rubella syndrome cases. 6, 5
• Breastfeeding is not a contraindication to MMR vaccination, even though rubella vaccine virus can be excreted in breast milk and transmitted to infants (infection remains asymptomatic). 2, 6

Special Timing Consideration

• If immune globulin was administered during pregnancy, delay MMR vaccination until 5-6 months after IG administration to avoid interference with vaccine immunogenicity from passively acquired antibodies. 6
• If MMR is given after exposure to blood products (including anti-Rho(D) immunoglobulin), repeat serologic testing at ≥3 months post-vaccination to verify antibody development. 6

Common Pitfalls to Avoid

• Do not confuse measles (rubeola) with rubella (German measles)—they are different diseases with different fetal risks; immune globulin is indicated for measles exposure but not routinely for rubella exposure in pregnancy. 6
• Do not postpone vaccination for minor febrile illnesses or require routine physical examinations before vaccinating women who appear healthy. 2
• Do not assume that birth defects occurring after inadvertent vaccination are causally related—3-5% of all births have congenital anomalies regardless of vaccination status. 2

Pre-Vaccination Screening

• Ask all women of childbearing age if they are or may be pregnant before administering MMR. 2, 3
• Exclude those who state they are pregnant. 2
• Explain the theoretical risk and the need to avoid pregnancy for 3 months to those who will receive the vaccine. 2, 3