Can a Vaccinated Person Transmit Measles?
No, persons who receive MMR vaccine do not transmit measles, rubella, or mumps vaccine viruses. 1 The MMR vaccine provides effective protection not only for the vaccinated individual but also prevents them from becoming carriers who could transmit the virus to others.
Understanding MMR Vaccine and Transmission
The Advisory Committee on Immunization Practices (ACIP) clearly states that individuals who receive MMR or its component vaccines do not transmit measles, rubella, or mumps vaccine viruses 1. This is a critical distinction between natural infection and vaccination:
- Natural measles infection: Highly contagious with transmission occurring 4 days before rash onset through 4 days after rash onset
- MMR vaccination: No documented transmission of vaccine virus in healthcare settings
Vaccine Effectiveness in Preventing Transmission
The MMR vaccine is highly effective in preventing measles:
- 95% effectiveness after one dose 2
- 96% effectiveness after two doses 2
- 81-85% effectiveness in preventing household transmission after vaccination 2
This high effectiveness means that vaccinated individuals are protected from infection and therefore cannot transmit the virus to others.
Post-Exposure Prophylaxis
When exposure to measles occurs, the ACIP recommends:
- For most persons ≥12 months: MMR vaccination within 72 hours of exposure provides some protection 1
- For household contacts ≥6 months: Vaccine within 72 hours is acceptable 1
- For susceptible contacts when >72 hours have passed: Immune globulin (IG) is recommended 1
The effectiveness of post-exposure vaccination is approximately 74% 2, which helps prevent both illness in the exposed person and potential transmission to others.
Special Considerations
Immunocompromised Individuals
- Severely immunocompromised patients exposed to measles should receive immune globulin prophylaxis regardless of vaccination status 1
- MMR vaccine is contraindicated for post-exposure prophylaxis in immunocompromised persons 1
Healthcare Settings
- Healthcare personnel should have documented immunity to measles 1
- During outbreaks, all healthcare personnel should observe airborne precautions when caring for patients with measles, even if they have been vaccinated 1
- This is due to the small possibility (~1%) of vaccine failure 1
Common Pitfalls to Avoid
Confusing vaccine virus with wild-type virus: The attenuated viruses in the MMR vaccine do not cause transmissible infection, unlike the wild-type virus.
Assuming partial protection means potential for transmission: Even though vaccine effectiveness is not 100%, vaccinated individuals who do get infected would be infected with wild-type virus (not the vaccine strain), and this would be a breakthrough infection, not vaccine-related transmission.
Misunderstanding post-exposure vaccination: Administering MMR vaccine after exposure is a preventive measure to stop the exposed person from developing measles and potentially transmitting it, not a source of transmission itself.
In conclusion, a person vaccinated with MMR cannot transmit measles from an infected patient to a non-vaccinated individual. The vaccine prevents infection in the vaccinated person, thereby breaking the chain of transmission.