From the Guidelines
An immunized 10-year-old child is highly unlikely to contract measles, with the measles vaccine (MMR) being approximately 97% effective after two doses. The vaccine is typically given at 12-15 months and 4-6 years of age, and it produces an inapparent or mild, noncommunicable infection 1. In the rare case that a fully immunized child does contract measles (called vaccine breakthrough), the symptoms are usually much milder than in unimmunized individuals, with a shorter duration, less severe rash, minimal or no fever, and significantly reduced risk of complications.
Key Points to Consider
- The immune system, primed by vaccination, can mount a faster and more effective response to the virus, reducing disease severity 1.
- Studies indicate that, if the first dose is administered no earlier than the first birthday, greater than 99% of persons who receive two doses of measles vaccine develop serologic evidence of measles immunity 1.
- Although vaccination produces lower antibody levels than natural disease, both serologic and epidemiologic evidence indicate that the vaccine induces long-term -- probably lifelong -- immunity, in most persons 1.
- Parents should still monitor for any symptoms in the unlikely event of exposure, but can be reassured that serious illness is extremely rare in properly immunized children.
Recommendations for Practice
- All contacts of a measles case should be evaluated immediately for presumptive evidence of measles immunity, and those without evidence of immunity should be offered the first dose of MMR vaccine and excluded from work from day 5–21 following exposure 1.
- Available data suggest that live virus measles vaccine, if administered within 72 hours of measles exposure, will prevent, or modify disease 1.
Important Considerations
- Measles vaccine failure can occur, albeit rarely, and all health-care personnel (HCP) should observe airborne precautions in caring for patients with measles 1.
- HCP in whom measles occurs should be excluded from work until ≥4 days following rash onset, and contacts with measles-compatible symptoms should be isolated, and appropriate infection-control measures should be implemented to prevent further spread 1.
From the Research
Effect of Measles on a Previously Immunized Child
- The effect of measles on a previously immunized 10-year-old child with presumed immunity is likely to be less severe compared to unvaccinated children, as indicated by a study published in 2.
- Breakthrough measles cases, which occur in previously vaccinated individuals, tend to have milder disease with fewer complications, as reported in 2.
- A study published in 3 found that measles vaccine has a preventive effect on the development of complications, which suggests that previously immunized children may be less likely to experience severe symptoms.
Clinical Characteristics and Severity
- The clinical presentation and disease severity of measles in previously immunized children are influenced by factors such as vaccination status, age, and the number of doses received, as discussed in 2.
- Children aged 5-19 years tend to have fewer complications compared to other age groups, according to 2.
- A study published in 4 found that the risk of fever and seizures following immunization with measles-containing vaccines is lower when administered at 12 to 15 months of age.
Vaccine Failure
- Primary vaccine failure (PVF) and secondary vaccine failure (SVF) can occur in previously immunized individuals, with PVF being associated with a higher proportion of classic measles presentation and severe disease, as reported in 2.
- The majority of breakthrough infections are due to secondary vaccine failure (SVF), which tends to result in milder disease, as indicated by 2.