What is the recommended work‑up and post‑exposure prophylaxis for a person exposed to measles, including assessment of immunity, vaccination status, and appropriate use of measles‑mumps‑rubella (MMR) vaccine or measles immune globulin?

Measles Exposure Work-Up and Post-Exposure Prophylaxis

Immediately assess immunity status and administer MMR vaccine within 72 hours to all susceptible contacts aged ≥6 months (except pregnant women and immunocompromised persons), or give immune globulin within 6 days if MMR is contraindicated or the 72-hour window has passed. 1

Immediate Assessment of Immunity

Presumptive evidence of measles immunity includes: 1

• Two documented doses of MMR vaccine (first dose on/after first birthday, second dose ≥28 days later)
• Laboratory confirmation of measles IgG antibody (equivocal results = non-immune)
• Laboratory-confirmed measles disease
• Birth before 1957 (though healthcare facilities should still consider vaccinating these individuals with 2 doses of MMR if they lack laboratory evidence of immunity) 1

All exposed contacts without documented immunity require immediate intervention. 1

Post-Exposure Prophylaxis Algorithm

For Immunocompetent Non-Pregnant Contacts ≥12 Months

Administer MMR vaccine within 72 hours of exposure to prevent or modify disease—this is the preferred intervention for most settings including daycare, schools, colleges, and healthcare facilities. 1 Even if the 72-hour window has passed, give MMR anyway to provide future protection against measles, mumps, and rubella. 1

**If >72 hours but <6 days post-exposure and MMR was not given:** Consider immune globulin 0.25 mL/kg IM (maximum 15 mL) for household contacts, though this is generally not recommended for immunocompetent persons >12 months in non-household settings due to low complication risk and practical challenges. 1, 2

For Infants <12 Months

Infants 6-12 months: 1

• Give MMR within 72 hours of exposure (acceptable for household contacts ≥6 months)
• If identified after 72 hours but within 6 days: Give IM immune globulin 0.5 mL/kg (maximum 15 mL) 2
• Critical caveat: Any infant vaccinated before 12 months must be revaccinated with 2 doses of MMR starting on/after the first birthday, separated by ≥28 days 1

Infants <6 months: 1

• Usually immune from maternal antibodies
• If mother has measles or infant lacks maternal immunity: Give IM immune globulin 0.5 mL/kg (maximum 15 mL) within 6 days 2

For Pregnant Women

Give IM immune globulin 0.25 mL/kg (maximum 15 mL) within 6 days of exposure. 1 MMR vaccine is contraindicated in pregnancy. 1 If injection volume is a concern or weight ≥30 kg, consider IV immune globulin 400 mg/kg instead. 2

For Immunocompromised Persons

Give immune globulin 0.5 mL/kg IM (maximum 15 mL) within 6 days of exposure, regardless of vaccination status. 1 Alternatively, if injection volume is problematic or weight ≥30 kg, give IV immune globulin 400 mg/kg. 2, 3 MMR vaccine is contraindicated in severely immunocompromised patients. 1

For patients already receiving regular IGIV therapy: A standard dose of 100-400 mg/kg within 3 weeks before exposure should be sufficient; if exposed >3 weeks after IGIV, consider an additional dose. 1

Quarantine and Exclusion Periods

Healthcare Personnel Without Immunity

If vaccinated post-exposure: Exclude from work days 5-21 after exposure. 1

If not vaccinated post-exposure (even if given IG): Exclude from all patient contact days 5-21 after first exposure through day 21 after last exposure. 1

Healthcare workers with only 1 documented MMR dose: May remain at work but must receive second dose immediately. 1

Non-Healthcare Contacts

Quarantine until 21 days after exposure if: 1

• No evidence of immunity
• Did not receive MMR or immune globulin

If immune globulin was administered: Monitor for 28 days (not 21) because IG prolongs the incubation period. 1

Critical Infection Control Measures

All healthcare workers caring for measles patients must wear N95 respirators regardless of immunity status because vaccine failure occurs in ~1% of vaccinated individuals. 1 Regular surgical masks are insufficient for airborne transmission. 4

Place suspected/confirmed measles patients in negative-pressure airborne isolation rooms immediately. If unavailable, use a private room with the door closed. 4 Patients should wear medical masks upon arrival. 4

Measles patients are contagious from 4 days before rash onset through 4 days after rash onset—maintain isolation for the full 4 days after rash appears. 1, 4, 5

Common Pitfalls to Avoid

Do not rely on serology after exposure—there is no time to wait for antibody results. Act immediately based on vaccination documentation. 1

Do not forget that persons born before 1957 may still need vaccination in healthcare settings or during outbreaks, despite presumed natural immunity. 1

Do not use standard IM immune globulin doses (0.25 mL/kg) for immunocompromised patients or infants <6 months—these groups require 0.5 mL/kg. 1, 2

Do not assume MMR given after 72 hours is useless—it still provides future protection even if it doesn't prevent the current exposure. 1

Do not allow healthcare workers to return to work on day 21 if they develop symptoms—anyone with measles must remain excluded until ≥4 days after rash onset. 1