Management of Side Effects After MMR Vaccination
Most side effects after MMR vaccination are mild, self-limited, and require only symptomatic management, with serious adverse events occurring at a rate of approximately 5 per 100,000 vaccinees. 1, 2
Common Side Effects and Their Management
Fever
- 5-15% of vaccinees develop fever ≥103°F (≥39.4°C) beginning 5-12 days after vaccination, lasting several days 1
- Most persons with fever are otherwise asymptomatic and require only supportive care 1
- Fever typically resolves without intervention 1
Rash
- Transient rashes occur in approximately 5% of vaccinees 1
- These are self-limited and do not require specific treatment 1
- The rash typically appears within 2 weeks of vaccination 1
Febrile Seizures
- Simple febrile seizures can occur in children, particularly those with personal or family history of seizures 1
- Febrile seizures following MMR vaccination do not increase the probability of subsequent epilepsy or other neurologic disorders 1
- Management is supportive, as with any febrile seizure 1
Rare but Serious Adverse Events
Thrombocytopenia
- Clinically apparent thrombocytopenia occurs in 1 per 30,000-40,000 vaccinated children, with temporal clustering 2-3 weeks post-vaccination 1
- The clinical course is usually transient and benign, though hemorrhage occurs rarely 1
- Children with prior idiopathic thrombocytopenic purpura are at higher risk for recurrence after MMR 1
- For patients with history of thrombocytopenia within 6 weeks of previous MMR dose, consider checking serologic evidence of measles immunity rather than revaccinating 1
Allergic Reactions
Minor Reactions
- Most hypersensitivity reactions are minor, consisting of wheal and flare or urticaria at the injection site 1
- These require only symptomatic management 1
Anaphylaxis
- Immediate anaphylactic reactions are extremely rare: only 11 confirmed cases among >70 million doses distributed 1
- Anaphylactic reactions are not associated with egg allergy but rather with other vaccine components, particularly gelatin 1
- Persons with history of anaphylactic reaction to gelatin or neomycin should not receive MMR 1
- Egg allergy, even with history of anaphylaxis to eggs, is NOT a contraindication to MMR vaccination 1
Neurologic Events
- CNS conditions including encephalitis occur at a frequency of <1 per million doses 1
- The incidence of encephalitis after MMR vaccination is lower than the background rate of encephalitis of unknown etiology, suggesting temporal rather than causal association 1
Key Management Principles
When to Observe vs. Intervene
- Minor illnesses with low-grade fever are NOT contraindications to vaccination and do not require specific management 1
- Moderate to severe febrile illnesses warrant postponing vaccination until recovery to avoid confounding adverse effects with underlying illness 1
Documentation and Reporting
- True adverse reactions causally related to MMR are rare (0.5-4.0% based on controlled studies) 3
- 45% of reported serious adverse events are actually caused by concurrent factors unrelated to vaccination 2
- Comprehensive analysis is needed to establish causality beyond temporal association 2
Common Pitfalls to Avoid
- Do not assume all post-vaccination symptoms are vaccine-related: respiratory symptoms, nausea, and vomiting may occur more frequently in unvaccinated controls 3
- Do not withhold vaccination due to egg allergy: special protocols and skin testing are not necessary for egg-allergic persons 1
- Do not confuse contact dermatitis to neomycin with anaphylaxis: contact dermatitis is not a contraindication to MMR 1
- Do not revaccinate persons with severe thrombocytopenia within 6 weeks of prior MMR dose without checking serologic immunity first 1