Can I still get measles after receiving the Measles, Mumps, and Rubella (MMR) vaccine?

Can You Still Get Measles After MMR Vaccination?

Yes, you can still get measles after MMR vaccination, but it's extremely rare—approximately 5% of people fail to develop immunity after one dose, which is why two doses are now standard. 1, 2

Understanding Vaccine Failure vs. Vaccine-Related Symptoms

The most likely explanation for measles-like symptoms after MMR vaccination is a normal vaccine reaction, not actual measles disease:

• Approximately 5% of vaccinated persons develop a transient measles-like rash 7-10 days after vaccination as the live attenuated virus replicates on a limited scale 2, 3
• These symptoms include fever, conjunctivitis, and rash occurring 5-14 days post-vaccination 3
• This is a vaccine reaction, not wildtype measles infection, and does not indicate vaccine failure 3

True Vaccine Failure: Primary vs. Secondary

Primary vaccine failure occurs when immunity never develops:

• Affects approximately 5% of recipients after the first dose 1
• This is why two doses of MMR are now recommended—the second dose provides immunity to nearly all who didn't respond to the first dose 1
• The major benefit of the second dose is reducing the proportion who remain susceptible due to primary vaccine failure 1

Secondary vaccine failure (waning immunity):

• Waning immunity is not a major cause of vaccine failure and has little influence on measles transmission 1
• Revaccination of children with low antibody levels produces only a transient rise 1

High-Risk Scenarios for Inadequate Protection

Certain populations may have suboptimal protection and should be evaluated:

Adults with inadequate childhood vaccination:

• Those vaccinated before 12 months of age may have suboptimal protection 2
• Persons vaccinated during 1963-1967 may have received inactivated (killed) vaccine, which provides no lasting immunity 1
• Anyone who received killed measles vaccine requires revaccination with two doses of live MMR vaccine 1, 2

During outbreaks:

• Even persons born before 1957 (presumed immune) should be considered for MMR during mumps outbreaks if they may be susceptible 1
• In the 2006 mumps outbreak, 44% of cases occurred in persons who had received 2 doses of mumps-containing vaccine, demonstrating that breakthrough infections can occur but remain uncommon 1

Clinical Approach to Suspected Measles After Vaccination

If symptoms occur 7-14 days after recent MMR vaccination:

• This is most likely a vaccine reaction, not wildtype measles 3
• The low incidence of wildtype measles strongly suggests symptoms within 14 days of vaccination are vaccine-related 3
• Elaborate diagnostic procedures may cause unnecessary parental stress; reassurance is more appropriate 3

If true measles exposure occurred:

• Specimens should be submitted for viral strain identification to distinguish vaccine strain from wildtype virus 1
• If an exposed person is already incubating measles, MMR vaccination will not exacerbate symptoms 1

Risk-Benefit Analysis

The benefits of vaccination far outweigh the minimal risk of vaccine failure:

• Natural measles infection carries substantially higher risks of serious complications, including encephalopathy 2
• Even recipients of inactivated measles vaccine who experience adverse reactions to live vaccine revaccination (ranging from 4-55% with mostly mild reactions) face greater risk from natural measles infection than from the vaccine 1

Common Pitfalls to Avoid

• Don't assume all measles-like symptoms after vaccination represent vaccine failure—they are usually normal vaccine reactions 3
• Don't rely on birth year alone (before 1957) as proof of immunity during outbreaks 1
• Don't forget to verify vaccination history—those vaccinated 1963-1967 may need complete revaccination 1
• Don't overlook international travel risk—revaccination should be considered before travel to measles-endemic areas, even with previous vaccination 4