PB1215 - Exacerbation of Immune Thrombocytopenia Following Initial and Booster Vaccination with Pfizer-BioNTech COVID-19 Vaccine

Background: There is emerging data on immune thrombocytopenia (ITP) exacerbation after initial Covid-19 vaccination. The rate of ITP exacerbation after booster vaccines is unknown.

Aims: Explore rates of ITP exacerbation after first, second and booster Pfizer-BioNTech COVID-19 vaccines in adult ITP patients.

Methods: Retrospective study of ITP patients, receiving 1-3 doses of Pfizer-BioNTech vaccine. The primary outcome was clinical ITP exacerbation defined as platelet count decrease requiring initiation or escalation of ITP treatment and/or a new medical attention due to bleeding, within 3 months. Secondary outcome was any clinically-relevant platelet decrease during the 3 months post-vaccination compared to pre-vaccine count, defined as platelet decrease to ≤30×109/L or thrombocytopenia with >50% decrease from baseline.

Results: The study included 93 ITP patients (83 with chronic ITP) receiving 1 (n=2), 2 (n=22) or 3 (n=69) vaccine doses. ITP exacerbation occurred in 2/93 (2.2%) patients following first/second dose, and 3/69 (4.3%) following booster dose. Clinically-relevant platelet decreases after initial doses occurred in 8/72 (11.1%) patients with platelet counts available, and in 8/39 (20.5%) after the booster, within a median 18 and 20 days. Table 1 shows clinical data and platelet counts in patients experiencing primary or secondary outcomes.
Clinical ITP exacerbation after booster doses was preceded by a clinically-relevant platelet decrease after the initial doses in 1 of 3 patients, but not by clinical exacerbations. Four of 8 patients (50%) with clinically-relevant platelet decreases after booster doses also had clinically-relevant decreases following initial vaccination.

Conclusion(s): Clinical ITP exacerbation in chronic ITP patients is infrequent following Pfizer-BioNTech COVID-19 vaccine. Clinical exacerbation after booster doses was not preceded by clinical exacerbation after initial doses in this study. Clinically-relevant platelet decreases after booster doses occur frequently in patients with clinically relevant decreases after initial doses. This suggests monitoring of platelet counts in ITP patients receiving COVID-19 vaccines.