Immune thrombocytopenia following immunisation with Vaxzevria ChadOx1-S (AstraZeneca) vaccine, Victoria, Australia

Vaccine. 2021 Nov 26;39(48):7052-7057. doi: 10.1016/j.vaccine.2021.10.030. Epub 2021 Oct 30.


Emerging evidence suggest a possible association between immune thrombocytopenia (ITP) and some formulations of COVID-19 vaccine. We conducted a retrospective case series of ITP following vaccination with Vaxzevria ChadOx1-S (AstraZeneca) and mRNA Comirnaty BNT162b2 COVID-19 (Pfizer-BioNTech) vaccines and compare the incidence to expected background rates for Victoria during the first six months of the Australian COVID-19 vaccination roll-out in 2021. Cases were identified by reports to the Victorian state vaccine safety service, SAEFVIC, of individuals aged 18 years or older presenting with thrombocytopenia following COVID-19 vaccination without evidence of thrombosis. Twenty-one confirmed or probable cases of ITP were identified following receipt of AstraZeneca (n = 17) or Pfizer-BioNTech (n = 4) vaccines. This translates to an observed incidence of 8 per million doses for AstraZeneca vaccine, twice the expected background rate of 4.1 per million. The observed rate for Pfizer-BioNTech was consistent with the expected background rate. The median time to onset for the cases post AstraZeneca vaccination was 10 days (range 1-78) and median platelet nadir 5 × 109/L (range 0-67 × 109/L). Hospital presentations or admissions for management of symptoms such as bleeding occurred in 18 (86%) of the cases. The majority of cases (n = 11) required intervention with at least 2 therapy modalities. In conclusion, we observed a substantially higher than expected rate of ITP following AstraZeneca vaccination. ITP is the second haematological adverse event, distinct from that of thrombosis with thrombocytopenia syndrome (TTS), observed following AstraZeneca vaccination.

Keywords: COVID-19; Immune thrombocytopenia; Vaccination; Vaccine.

MeSH terms

  • BNT162 Vaccine
  • COVID-19 Vaccines
  • COVID-19*
  • Humans
  • Purpura, Thrombocytopenic, Idiopathic* / chemically induced
  • Purpura, Thrombocytopenic, Idiopathic* / epidemiology
  • Retrospective Studies
  • SARS-CoV-2
  • Thrombocytopenia*
  • Vaccination
  • Vaccines*
  • Victoria / epidemiology


  • COVID-19 Vaccines
  • Vaccines
  • BNT162 Vaccine