Background
Discoloured leg syndrome (DLS) is a rare phenomenon that can occur after receipt of an injected vaccine. It is a transient condition involving either an even or patchy colour change to the skin in the lower extremities (red, blue or purple) and may or may not involve petechiae (pin-point red spots on the skin) or swelling.
Diagnosis
DLS is be diagnosed based on clinical presentation (e.g. symptom profile, onset of symptoms and symptom resolution).
Unlike injection site reactions (ISRs), DLS does not radiate from the site of injection, and can impact one or both legs, even if only one injection has been administered. Discolouration can also extend up to the pelvis.
Investigations are generally not required. Despite the presence of petechiae, there is no drop in platelet count.
As DLS involves skin changes and symptoms can occur quickly, it is important to differentiate it from anaphylaxis, especially if symptoms start within 30 minutes of vaccination.
Association and incidence
DLS is reported at a rate of 58 per 100,000 children vaccinated. Although the median onset time for colour change is approximately 3.5 hours, DLS can be seen quite quickly post-vaccination (within 30 minutes). Where symptoms of petechiae occur, the median onset time is 12 hours following vaccination. Generally, colour change (median duration = approximately 2 hours) does not last as long as petechiae (median duration = 54 hours).
Treatment
As a precaution, assessment of airway, breathing and circulation is advised.
Symptoms of DLS are transient and will resolve on their own without treatment.
Any adverse event following immunisation (AEFI), including DLS, should be reported to the adverse event reporting service in your jurisdiction. In Victoria, this is SAEFVIC.
Implications for future doses
Recurrence of DLS is uncommon, but can occur. However, DLS is not a contraindication to receiving future vaccines. Given that DLS appears to be age-related, families can be reassured that children are less likely to experience symptoms as they get older.
Resources
Authors: Rachael McGuire (MVEC Education Nurse Coordinator), Dr Shidan Tosif (Senior Research Fellow, SAEFVIC) and Prof Nigel Crawford (Director, MVEC).
Date: April 2026
Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.
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