Do Splenectomized Immune Thrombocytopenia (ITP) Patients Have Increased Risks for Platelet Decreases Following COVID-19 Vaccination?
Authors: MacWhirter - DiRaimo Jennifer , Kruse Caroline , Bussel James B , Kruse Alexandra 
Published: November 2021

Abstract

BACKGROUND AND AIMS
Fear of receiving protective vaccinations against the COVID-19 virus is high among patients with immune thrombocytopenia (ITP), an autoimmune bleeding disorder, due to uncertainty around effects on platelet count (PC) reactivity. Decreases in PC have been previously reported, including decreases of &gt;100,000/µL including a need for rescue treatment in a small fraction of patients. For ITP patients, a further reduction in PC could trigger bleeding symptoms that require hospitalization and additional treatments. Here, we report on differences in PC changes between not-splenectomized (NS) and (Spl) splenectomized adult ITP patients to explore if Spl ITP patients have a greater risk for PC decreases following COVID-19 vaccination.
Methods
Data were collected using the ITP COVID-19 web-based survey that is part of the Platelet Disorder Support Association's ITP Natural History Study Patient Registry. As of June 2021, 241 adults with ITP had received at least one vaccine dose, a post vaccine PC, and had disclosed their splenectomy status. Comparisons were made between Spl and NS groups focusing on quantitative differences in reported PC changes post-vaccination. Data was analyzed using descriptive statistics, chi-square analysis, and Fisher exact tests.
Results
Following Dose#1 (D1):
For the Spl group (n=59), 2 (4%) experienced a PC increase from baseline, 38 (64%) reported their count remained unchanged, and 19 (32%) experienced a decrease. Within the NS group (n=182), 35 (19%) experienced an increased PC, for 89 (49%) the count remained unchanged, and 58 (32%) had a decrease. PC differences between the Spl and NS groups following D1 were significant (p = .018) using a Fisher exact test.
Regarding large decreases in PC, 13 Spl patients (22%) experienced a decrease &gt;50,000/µL and 6 (10%) a decrease &gt;100,000/µL. Within the NS group, 15 (8%) experienced a PC decrease &gt;50,000/µL and 5 (3%) a decrease &gt;100,000/µL. Differences in large PC changes following D1 between both groups were significant (X 2 = 8.254 ; p =.004).
Following Dose#2 (D2):
For the Spl group (n=34), comparing their post-vaccination count to their typical baseline count, 1 (3%) experienced an increased PC, 26 (76%) reported their PC remained unchanged, and 7 (21%) experienced a decreased PC. Within the NS group (n=103) comparing their post-vaccination count to their typical baseline count, 17 (17%) experienced an increased PC, 56 (54%) reported their PC remained unchanged, and 30 (29%) experienced a decreased PC. These differences were not statistically significant.
Within the Spl group, 3 out of 34 (9%) experienced a large PC decrease &gt; 50,000/µL, all 3 &gt;100,000/µL. Within the NS group, only 5 out of 103 (5%) experienced a PC decrease &gt;50,000/µL with only 1 &gt;100,000/µL. The Spl group experienced more PC decreases &gt;100,000/µL compared to the NS group following D2; this difference was statistically significant (p = .047) using a Fisher exact test.

Comparison of D1 and D2
Although more PC decreases were reported in both the Spl and NS group after receipt of D1 compared to D2, this difference was not statistically significant. Comparison between Spl and NS participants with the same PC result (increase, decrease, or no change) following both D1 and D2 (n=133) did not reveal a statistically significant difference; within the NS group (n=101), 73 (73%) reported the same result while for the Spl group (n=32) 25(78%) experienced the same result. Regardless of splenectomy status (n=133), 62 (72%) participants experienced the same PC result for D1 and D2.

Conclusion
Fear of a post-vaccination PC decrease, especially a large decrease, may influence an ITP patient's decision to accept or refuse vaccination. Spl participants were more likely than those NS to experience larger (&gt;50,000/µL) albeit transient decreases in their PC following vaccination. However, the overall risk for large PC decreases is minimal among individuals with ITP, even among those who have had a splenectomy. Our results should provide reassurance to most ITP patients and reduce vaccine hesitancy, especially for those who have not undergone splenectomy; those who have can readily be vaccinated with close monitoring and planning with a hematologist familiar with ITP. Additional studies could focus on identifying more specific factors affecting PC changes post vaccination which in turn would lead to better understanding of platelet variability in ITP patients.

Disclosures
MacWhirter - DiRaimo: JD has not personally received any payment personally, but PDSA has received grants and consultancy fees from Novartis, grant and honorarium from Amgen, grant and consultancy fees from Pfizer and UCB, and grants from Argenx, Principia, Rigel, and CSL Behr: Consultancy, Honoraria, Other. Kruse: CK has not personally received payment but reports that PDSA received grants and consultancy fees from Novartis, grant and honorarium from Amgen, grant and consultancy fees from Pfizer and UCB, and grants from Argenx, Principia, Rigel, and CSL Behring: Consultancy, Honoraria, Other. Bussel: CSL: Other: DSMB; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; UptoDate: Honoraria; Rigel: Consultancy, Membership on an entity's Board of Directors or advisory committees; UCB: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: DSMB; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Dova/Sobi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Principia/Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Momenta/Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; RallyBio: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Kruse: Alex has not personally received any payment but reports that PDSA received grants and consultancy fees from Novartis, grant and honorarium from Amgen, grant and consultancy fees from Pfizer and UCB, and grants from Argenx, Principia, Rigel, and CSL Behri: Consultancy, Honoraria, Other.