From the Guidelines
Measles vaccination is not recommended for children younger than 6 months old due to several potential risks, including interference with the vaccine's effectiveness by maternal antibodies and potential for more severe reactions in very young infants. The standard MMR (measles, mumps, rubella) vaccine is typically given at 12-15 months of age because maternal antibodies present in infants under 6 months can interfere with the vaccine's effectiveness, rendering it less protective 1. If given too early, the vaccine may not produce an adequate immune response, leaving the child vulnerable to measles later. Additionally, the live attenuated virus in the MMR vaccine could potentially cause more severe reactions in very young infants whose immune systems are still developing.
Potential Risks and Side Effects
Some potential side effects that might occur include:
- Fever (sometimes high)
- Mild rash
- Temporary pain at the injection site
- Rarely, febrile seizures In special circumstances such as during outbreaks or before international travel to high-risk areas, vaccination may be considered for infants 6-11 months old, but this would be followed by the regular two-dose schedule starting at 12-15 months, as the early dose is not counted toward the routine series due to potentially reduced effectiveness 1. The Advisory Committee on Immunization Practices (ACIP) has recommended a second MMR vaccine, PRIORIX, as an option to prevent measles, mumps, and rubella according to the existing recommended schedules and for off-label uses, including infants aged 6–11 months who will travel or live abroad or during measles outbreaks 1.
From the Research
Potential Risks of MMR Vaccination to Infants Younger than 6 Months Old
- The MMR vaccine is not typically recommended for infants younger than 6 months old, as the risk of measles infection is high in this age group and the vaccine may not be effective due to the presence of maternal antibodies 2, 3.
- Infants younger than 6 months old may not respond well to the MMR vaccine, with one study showing that only 67% of 6-month-old infants achieved seroprotective neutralizing antibody titers after vaccination 3.
- The Advisory Committee on Immunization Practices (ACIP) recommends that infants younger than 6 months old who are exposed to measles receive immune globulin administered intramuscularly (IGIM) or intravenously (IGIV) as post-exposure prophylaxis, rather than the MMR vaccine 4.
- The German Standing Committee on Vaccination (STIKO) also recommends passive immunization with immunoglobulins as post-exposure prophylaxis for infants younger than 6 months old, as well as for immunocompromised patients and pregnant women 5.
- The efficacy of passive immunization in preventing measles depends on the timing of administration, the concentration of measles antibodies in the immunoglobulin products, and the dosage 6, 5.
Post-Exposure Prophylaxis for Infants Younger than 6 Months Old
- The National Advisory Committee on Immunization (NACI) recommends that susceptible infants younger than 6 months old receive intramuscular immunoglobulin (IMIg) at a concentration of 0.5 mL/kg, to a maximum dose of 15 mL, if injection volume is not a major concern 6.
- The ACIP recommends that infants younger than 6 months old who are exposed to measles receive IGIM or IGIV as post-exposure prophylaxis, with the dose and route of administration depending on the individual's risk factors and medical history 4.
- The STIKO recommends a single intravenous administration of immunoglobulins (400 mg/kg body weight) as soon as possible, preferably within six days, after exposure to measles, for infants younger than 6 months old, susceptible pregnant women, and immunocompromised patients 5.