Rubella re-infection

• this phenomenon can occur in individuals with both vaccine-induced antibody and antibody secondary to a previous natural infection
  
  
  • there have been cases of congenital rubella syndrome reported after rubella re-infection - however although the fetal risk of infection cannot be quantified, the risk is considered to be low (1)
• rubella re-infection in pregnancy
  • risk of asymptomatic reinfection to the fetus in the first 12 weeks of pregnancy is difficult to determine, since few prospective studies have been conducted
    • congenital infection occurs in about 8%, but the risk of defects is probably less than 5%, substantially less than the risk from primary rubella
      • it is therefore important to differentiate reinfection from primary rubella in pregnancy
        
        
• diagnosis of rubella re-infection
  • indicated by a significant rise in rubella IgG antibodies, sometimes to very high levels, in a woman with pre-existing antibodies
  • rubella IgM is also detected in sera taken within 4-6 weeks after rubella contact
  • ideally - pre-existing rubella antibodies should ideally be confirmed by retesting a stored serum sample
    • if a previous serum is not available, two previous laboratory reports of antibodies >=10 IU/ml or a single serum with antibodies >=10 IU/ml obtained after documented rubella vaccination are accepted as evidence of pre-existing immunity
    • without this evidence, supplementary tests may be required to obtain a diagnosis

It is currently not possible to identify those women at risk of reinfection, but it is more common in vaccinees than in those with naturally acquired immunity.

Reference:

• (1) The Green Book. Immunisation against infectious disease. HMSO. London 1996.
• (2) Best JM. Rubella. Semin Fetal Neonatal Med. 2007 Jun;12(3):182-92