MMR Vaccine

MMR vaccine is a combined live attenuated vaccine containing weakened forms of measles, mumps, and rubella viruses. The vaccine viruses replicate in the host to produce a modified, subclinical infection that stimulates immunity without causing disease. MMR is among the most successful public health interventions in history.

Three Diseases Prevented

Measles — a highly contagious viral disease (R₀ 12–18) that causes fever, rash, cough, runny nose, and conjunctivitis. Complications include pneumonia, encephalitis, and death (1–3 per 1000 cases), as well as the rare and fatal late complication subacute sclerosing panencephalitis (SSPE).

Mumps — viral disease causing painful swelling of the salivary glands. Complications include meningitis, encephalitis, orchitis (with potential infertility), oophoritis, pancreatitis, and permanent hearing loss.

Rubella — usually mild in children, but causes severe Congenital Rubella Syndrome (CRS) when contracted in pregnancy (especially first trimester): deafness, cataracts, congenital heart defects, intellectual disability, microcephaly, miscarriage, or stillbirth. Preventing CRS is the primary goal of rubella vaccination.

Mechanism of Action

The live attenuated vaccine viruses replicate at low levels in the recipient, producing mild or asymptomatic infection that triggers a robust adaptive immune response — both humoral (IgG antibody production) and cellular (T-cell mediated) immunity. Antibodies develop 2–4 weeks after vaccination and protection is typically lifelong after a complete two-dose series.

Efficacy after one dose: measles 93%, mumps 78%, rubella 97%. Efficacy after two doses: measles 97%, mumps 88%, rubella 97%.

Real-world impact: measles has been eliminated in many countries with high vaccination coverage; congenital rubella syndrome has been eliminated in the Americas and several European countries; mumps outbreaks are now rare.

Safety: MMR has an excellent safety record across decades and millions of doses. Extensive research has definitively disproven any link between MMR and autism.

Routine childhood vaccination (2-dose series):

• Dose 1 at 12–15 months of age.
• Dose 2 at 4–6 years of age (before school entry).
• Minimum interval between doses: 4 weeks.

Priorix is licensed for active immunisation from 9 months of age. Infants vaccinated between 9 and 12 months should receive a second dose in the second year of life (preferably within 3 months of the first dose) because of possible interference from maternal antibodies. Safety and efficacy below 9 months have not been established.

Catch-up vaccination: 2 doses at least 4 weeks apart for unvaccinated adolescents and adults, or anyone born after 1957 without evidence of immunity.

High-priority groups for catch-up: healthcare workers, international travelers, college students, military recruits, non-pregnant women of childbearing age.

Post-exposure prophylaxis: within 72 hours of measles exposure, MMR may prevent or modify disease (not effective for mumps or rubella post-exposure).

Outbreak settings: infants 6–11 months may be vaccinated, but the dose does not count toward the routine 2-dose series — they still need 2 doses after 12 months of age.

Evidence of immunity: 2 documented MMR doses, laboratory evidence of immunity, or birth before 1957 (presumed immunity).

• Severe allergic reaction (anaphylaxis) to any vaccine component or to a previous dose.
• Pregnancy (theoretical risk to fetus).
• Severe immunodeficiency: primary immunodeficiency, HIV with severe immunosuppression (CD4 <15%), leukemia, lymphoma, active chemotherapy, high-dose systemic corticosteroids (>2 mg/kg/day or >20 mg/day for ≥2 weeks), other immunosuppressive therapy.
• Family history of congenital immunodeficiency unless immune competence is confirmed in the recipient.
• Active untreated tuberculosis.

Defer vaccination for moderate or severe acute illness, recent immunoglobulin or blood product administration (defer 3–11 months depending on product), or severe thrombocytopenia after a previous dose.

Not contraindications: HIV with adequate immune function, mild illness, antibiotic allergy, contact dermatitis to neomycin, tuberculin skin test, breastfeeding, immunocompromised household contact, low-dose or topical corticosteroids.

Egg allergy: Priorix is produced in chick embryo cell culture and may contain trace egg protein. Individuals with a history of anaphylaxis to egg ingestion should be vaccinated with extreme caution and adequate treatment for anaphylaxis on hand. Routine egg-allergic individuals without anaphylactic history can be safely vaccinated.

Excipient warnings: Priorix contains 334 µg phenylalanine per dose — harmful for individuals with phenylketonuria (PKU). It also contains 6.5 ng para-aminobenzoic acid, which may cause allergic (possibly delayed) reactions and exceptionally bronchospasm.

Most reactions are mild and typically occur 7–12 days after vaccination, when vaccine viruses are replicating.

Very Common (>10%): injection site pain/redness/swelling; fever (days 7–12); mild measles- or rubella-like rash (days 7–14, non-contagious).

Common (1–10%): injection site induration, upper respiratory symptoms, parotid/salivary gland swelling, diarrhea, vomiting, irritability.

Uncommon (0.1–1%): febrile seizures (days 7–10, benign, no long-term effects), arthralgia (more common in adolescents and adults), transient arthritis (more common in postpubertal females), lymphadenopathy, mild transient thrombocytopenia.

Rare (<0.1%): high fever (>39.5°C); anaphylaxis (~1 per million doses); immune thrombocytopenic purpura (1 per 30,000–40,000 doses, usually transient); seizures other than febrile.

Very Rare: encephalitis (~1 per million doses; lower than background rate, causality unclear); aseptic meningitis (extremely rare with current vaccine strains).

No association with: autism, inflammatory bowel disease, diabetes, multiple sclerosis, or chronic diseases — extensively studied and definitively disproven.

• Immunoglobulin and blood products: can interfere with vaccine response. After MMR, wait 2 weeks before giving immunoglobulin. Before MMR, wait 3–11 months after immunoglobulin (depending on dose).
• Immunosuppressive therapy: contraindicated during high-dose immunosuppression. After chemotherapy, wait 3–6 months. After high-dose corticosteroids, wait 1 month.
• Tuberculin skin test (TST): MMR can transiently suppress TST reactivity. Administer TST on the same day as MMR or wait 4–6 weeks. IGRA blood tests are not affected.
• Salicylates: avoid for 6 weeks after MMR (theoretical Reye syndrome concern, though not documented).

Reconstitution

The vaccine is supplied as a lyophilized powder plus diluent. Add the diluent to the vial of powder, mix gently until completely dissolved, withdraw the entire 0.5 mL, and use immediately. The reconstituted solution should be clear to slightly opalescent and peach-colored. Discard if discolored, particulate, or not used within 8 hours.

Route and Injection Site

Subcutaneous injection is preferred; intramuscular is acceptable.

• Children <12 months: anterolateral thigh.
• Children ≥12 months and adults: deltoid area or anterolateral thigh.

Co-Administration

Can be given simultaneously with most other recommended childhood vaccines (DTaP/Tdap, IPV, Hib, hepatitis A and B, varicella, pneumococcal, meningococcal, HPV, oral rotavirus). If not given simultaneously, wait at least 4 weeks between live viral vaccines.

Pregnancy and Contraception

Confirm patient is not pregnant before vaccination (test if uncertain). Counsel about contraception. Avoid pregnancy for 1 month after vaccination. Inadvertent vaccination during pregnancy: no intervention is needed; risk is theoretical and there are no documented cases of CRS from vaccine virus.

Breastfeeding

Safe to vaccinate breastfeeding mothers. Vaccine virus may be excreted in breast milk but is not harmful to the infant.

Outbreak Response

Infants 6–11 months may be vaccinated during outbreaks; the dose does not count toward the routine series — revaccinate at ≥12 months and again at 4–6 years. The second routine dose may be given as early as 28 days after the first dose during outbreaks.

Travel

Infants 6–11 months traveling internationally to high-risk areas may be vaccinated before travel and then revaccinated routinely. Unvaccinated adults should ensure 2 doses before international travel.

Healthcare Workers

Should have 2 documented MMR doses or laboratory evidence of immunity.

• Lyophilized powder: store at 2–8°C, in the original package, protected from light. Do not freeze.
• Diluent: store at 2–8°C or room temperature. Do not freeze.
• After reconstitution: use immediately (preferred). May be stored at 2–8°C for up to 8 hours, protected from light. Discard after 8 hours.

Maintain cold chain during transport using insulated containers with ice packs and continuous temperature monitoring.

2 years when stored at 2–8°C. Do not use after the expiry date.

Prescription required. Available at pediatric clinics, healthcare facilities, and immunization centers. Must be administered by qualified healthcare professionals.