ITP before and after COVID-19 vaccinations: A national cohort study

ABSTRACT

Background: Immune thrombocytopenia (ITP) has been reported following COVID-19 vaccination. From a population of over 20 million eligible vaccine recipients in Australia, over 32 million doses have been administered 19,600,000 Pfizer BNT162b2 (BNT), 12,600,000 AstraZeneca ChAdOx1 nCoV-19 (ChAd), and 397,000 Moderna mRNA-1273. Aim(s) Describe a comprehensive series of ITP after vaccination with clinical outcomes. Method(s) After obtaining IRB approval (2021/ETH00723), we collected data on all ITP cases diagnosed by haematologists in Australia within six weeks of any COVID-19 vaccination. We analysed their outcomes using international consensus definitions of responses and WHO bleeding. Result(s) Demographics (n = 50), treatments, and platelet outcomes (Figures A and B). Bleeding was mostly minor 35/50 (70%) WHO score <2. Compared to relapses of prior ITP, new presentations of ITP were significantly associated with ChAd over BNT (OR 7.1 95% CI 1.7 to 25.7, p = 0.0124*). Most patients responded quickly and deeply Median TTR 4 days (IQR 2-7), median TTCR 7 days (IQR 4-19), overall RR 45/47 (96%), and CR 40/45 (89%). Gender, age, antecedent influenza vaccination and severity of thrombocytopenia had no significant impact on Bleeding at presentation, response rates, relapse rates, time to response, or the need for ongoing treatments at day 90. No patients presented with thrombosis. PF4 ELISA was positive in one of 18 cases after ChAd (functional testing was negative). Conclusion(s) We diagnosed ITP more frequently after ChAd than BNT vaccination, occurring de novo after 1st doses. Ascertainment bias cannot be excluded due to greater scrutiny for platelet related complications, but almost all patients in this cohort needed treatment. Standard first-line treatments for ITP are highly effective for both de novo and prior ITP (96%), but second-line therapies are often required (34%). Our data reaffirms the safety of vaccinating patients with pre-existing ITP, as bleeding is mild (92% WHO < 2) and platelets respond quickly (TTCR 5 days).