From the Guidelines
Children who receive the Measles, Mumps, and Rubella (MMR) vaccination are at a higher risk for febrile seizures, fever, and measles-like rash, particularly within 5-12 days after vaccination.
Reactions to MMR Vaccination
- Febrile seizures: The risk of febrile seizures is approximately two times higher in children who receive the MMRV vaccine compared to those who receive the MMR vaccine and varicella vaccine separately, with an estimated one additional febrile seizure per 2,300-2,600 children vaccinated with MMRV vaccine 1.
- Fever: Fever is reported in 21.5% of MMRV vaccine recipients compared to 14.9% of MMR vaccine and varicella vaccine recipients, with a risk difference of 6.6% 1.
- Measles-like rash: Measles-like rash is observed in 3.0% of MMRV vaccine recipients compared to 2.1% of those receiving MMR vaccine and varicella vaccine, with a risk difference of 1.0% 1.
Timing of Reactions
- 5-12 days post-vaccination: The risk of febrile seizures, fever, and measles-like rash is higher during this period, with the peak in replication of the live attenuated measles virus occurring 6-12 days after vaccination 1.
Age Group Affected
- Children aged 12-23 months: The increased risk of febrile seizures, fever, and measles-like rash is most notable in this age group, although the risk may also be present in children aged ≤47 months 1.
Comparison to Separate Vaccinations
- MMR vaccine and varicella vaccine: The risk of febrile seizures, fever, and measles-like rash is lower when the MMR vaccine and varicella vaccine are administered separately compared to the combined MMRV vaccine 1.
From the Research
Adverse Reactions to MMR Vaccination
- Adverse events following immunization (AEFI) with the MMR vaccine have been reported, including parotitis, fever and convulsions, convulsions without fever, encephalopathy, and anaphylactic reactions 2
- The incidence of AEFIs following MMR vaccination has been found to be similar to rates reported in other studies, with parotitis being the most frequent event occurring in 1.8% of recipients 2
- Serious adverse events causally related to MMR vaccination are rare, with an incidence of 5.3 per 100,000 vaccinees or 3.2 per 100,000 vaccine doses, and are greatly outweighed by the risks of natural MMR diseases 3
Reactions in Specific Populations
- Children with egg allergy can be safely administered the MMR vaccine, and hospital admission for vaccination is not warranted for those with mild egg allergy 4
- Infants under nine months old who receive the MMR or MMRV vaccine may experience adverse events such as fever, injection reactions, and gastrointestinal symptoms, but these are generally not serious 5
Mechanism of Adverse Reactions
- Vaccine adverse events are thought to be related to the stimulation of innate immunity and the development of specific acquired immunity, with some adverse events related to autoimmune responses 6
- The pathogenicity of adverse reactions has been investigated, including anaphylactic reactions, systemic and local reactions following vaccinations, and the possibility of an association with autoimmune responses cannot be denied 6