Side effects

Adverse reactions following the MMR vaccine (except allergic reactions) are due to effective replication of the vaccine viruses with subsequent mild illness

• such events are to be expected in some individuals
  
  
  • events due to the measles component occur six to 11 days after vaccination
    
    
  • events due to the mumps and rubella components usually occur two to three weeks after vaccination but may occur up to six weeks after vaccination. These events only occur in individuals who are susceptible to that component, and are therefore less common after second and subsequent doses
    
    
  • if an individual has vaccine-associated symptoms are not infectious to others.

Common side effects:

• following the first dose of MMR vaccine, malaise, fever and/or a rash may occur, most commonly about a week after immunisation, and last about two to three days
  • parotid swelling occurred in about 1% of children of all ages up to four years, usually in the third week
• after a second dose of MMR vaccine, adverse reactions are considerably less common than after the first dose

Rare and more serious side effects:

• febrile seizures are the most commonly reported neurological event following measles immunisation. Seizures occur between the sixth to eleventh day in one in 1000 children vaccinated with MMR, a rate similar to that reported in the same period after measles vaccine
  • rate of febrile seizures following MMR is lower than that following measles disease
  • good evidence that febrile seizures following MMR immunisation do not increase the risk of subsequent epilepsy compared with febrile seizures due to other causes
    
    
• encephalitis
  • because MMR vaccine contains live attenuated viruses, it is biologically plausible that it may cause encephalitis
    • a large record linkage study in Finland, looking at over half a million children aged between one and seven years, did not identify any association between MMR and encephalitis
      
      
• ITP
  • another condition that may occur following MMR is ITP, most likely due to the rubella component
  • usually occurs within six weeks and resolves spontaneously. ITP occurs in about one in 22,300 children given a first dose of MMR in the second year of life
  • if ITP has occurred within six weeks of the first dose of MMR, then blood should be taken and tested for measles, mumps and rubella antibodies before a second dose is given
    
    
• arthropathy (arthralgia or arthritis) has also been reported to occur rarely after MMR immunisation, probably due to the rubella component
  • if it is caused by the vaccine, it should occur between 14 and 21 days after immunisation

Side effects of the vaccine include malaise, fever and rash after a week. Parotid swelling (after two weeks) and febrile convulsions can occur.

According to the Department of Health MMR vaccine should be given irrespective of a history of measles, mumps or rubella, or measles immunisation.

The evidence does not support the suggestions that MMR or MR vaccines cause autism or Crohn's disease (1).

Reference:

1. Immunisation Against Infectious Disease - "The Green Book".Chapter 21 Measles (April 2019).