From the Guidelines
Post-exposure prophylaxis for measles should be administered within 72 hours of exposure to prevent or modify the disease course, with MMR vaccine recommended as first-line prophylaxis for most individuals, as stated in the most recent guidelines 1. For those who cannot receive the vaccine, such as pregnant women, immunocompromised individuals, and infants under 6 months, immune globulin (IG) is recommended, administered within 6 days of exposure. The standard IG dose is 0.5 mL/kg of body weight (maximum 15 mL) given intramuscularly, as indicated in earlier guidelines 1. However, for severely immunocompromised patients, the dose may be higher, at 400 mg/kg intravenously. MMR vaccine works by stimulating the immune system to develop antibodies against measles virus before the infection can take hold, while immune globulin provides passive immunity through preformed antibodies that can neutralize the virus. Some key points to consider include:
- MMR vaccine can be administered to individuals aged 6 months and older, with a second dose given 28 days later for those who have not completed the two-dose series 1.
- Infants under 6 months may require IG for post-exposure prophylaxis, as they are not eligible for MMR vaccination.
- Immunocompromised individuals may require a higher dose of IG, and the effectiveness of IGIV in preventing measles is still uncertain 1. After receiving IG, MMR vaccination should be delayed for 3-11 months depending on the IG dose received. Individuals who receive post-exposure prophylaxis should still be monitored for symptoms of measles for 21 days after exposure, as breakthrough infections can occur, though they are typically milder. It is essential to follow the most recent guidelines for post-exposure prophylaxis, as recommendations may change over time, and to consult with a healthcare professional for specific guidance on individual cases.
From the Research
Post-Exposure Prophylaxis for Measles
- The National Advisory Committee on Immunization (NACI) recommends that susceptible immunocompetent individuals six months of age and older, who are exposed to measles and have no contraindications, be given measles-mumps-rubella (MMR) vaccine within 72 hours of the exposure 2.
- For susceptible infants younger than six months of age, NACI recommends intramuscular immunoglobulin (IMIg) at a concentration of 0.5 mL/kg, to a maximum dose of 15 mL administered over multiple injection sites, if injection volume is not a major concern 2.
- The Advisory Committee on Immunization Practices (ACIP) recommends the use of immune globulin administered intramuscularly (IGIM) for infants aged birth to 6 months exposed to measles, and increasing the recommended dose of IGIM for immunocompetent persons 3.
- A study on the effectiveness of measles vaccination and immune globulin post-exposure prophylaxis in an outbreak setting found that the effectiveness of MMR PEP was 83.4% and the effectiveness of IG PEP was 100% 4.
- A systematic review on post-exposure prophylaxis for the prevention of measles found that estimates of effectiveness ranged from 76% to 100% for Ig PEP, and from 83.4% to 100% for MCV PEP 5.
- Another study found that passively acquired antibody may interfere with the active antibody response to live viral vaccines such as measles and rubella, and that high doses of immune globulin (> 10 mg/kg) may inhibit the antibody response to measles for more than 3 months 6.
Recommendations for Special Populations
- NACI recommends that susceptible contacts who are pregnant or immunocompromised receive IMIg at a concentration of 0.5 mL/kg, understanding that recipients 30 kg or more will not receive the measles antibody concentrations that are considered to be fully protective 2.
- Alternatively, in cases where injection volume is a major concern or for recipients 30 kg or more, intravenous immunoglobulin (IVIg) can be provided at a dose of 400 mg/kg 2.
- ACIP recommends the use of immune globulin administered intravenously (IGIV) for severely immunocompromised persons and pregnant women without evidence of measles immunity who are exposed to measles 3.
Effectiveness of Post-Exposure Prophylaxis
- The effectiveness of MMR PEP and IG PEP has been found to be high, with estimates ranging from 76% to 100% 4, 5.
- However, the data on the effectiveness of post-exposure prophylaxis is limited, and more research is needed to estimate the effectiveness of measles PEP in populations of special interest, including immunocompromised and/or pregnant populations 5.