Thrombocytopenia including immune thrombocytopenia after receipt of mRNA COVID-19 vaccines reported to the Vaccine Adverse Event Reporting System (VAERS)

Vaccine. 2021 Jun 8;39(25):3329-3332. doi: 10.1016/j.vaccine.2021.04.054. Epub 2021 Apr 30.


Background: The objective of this study is to assess cases of thrombocytopenia, including immune thrombocytopenia (ITP), reported to the Vaccine Adverse Event Reporting System (VAERS) following vaccination with mRNA COVID-19 vaccines.

Methods: This case-series study analyzed VAERS reports of thrombocytopenia after vaccination with Pfizer-BioNTech COVID-19 Vaccine or Moderna COVID-19 Vaccine.

Results: Fifteen cases of thrombocytopenia were identified among 18,841,309 doses of Pfizer-BioNTech COVID-19 Vaccine and 13 cases among 16,260,102 doses of Moderna COVID-19 Vaccine. The reporting rate of thrombocytopenia was 0.80 per million doses for both vaccines. Based on an annual incidence rate of 3.3 ITP cases per 100,000 adults, the observed number of all thrombocytopenia cases, which includes ITP, following administration of mRNA COVID-19 vaccines is not greater than the number of ITP cases expected.

Conclusions: The number of thrombocytopenia cases reported to VAERS does not suggest a safety concern attributable to mRNA COVID-19 vaccines at this time.

Keywords: Immune thrombocytopenia; Thrombocytopenia; VAERS; mRNA COVID-19 vaccines.

MeSH terms

  • Adult
  • Adverse Drug Reaction Reporting Systems
  • COVID-19 Vaccines
  • COVID-19*
  • Humans
  • Purpura, Thrombocytopenic, Idiopathic* / epidemiology
  • RNA, Messenger
  • SARS-CoV-2
  • Thrombocytopenia* / chemically induced
  • Thrombocytopenia* / epidemiology
  • United States
  • Vaccines* / adverse effects


  • COVID-19 Vaccines
  • RNA, Messenger
  • Vaccines