COVID-19 Vaccination in Children and Young Adults with Pre-Existing Immune Thrombocytopenia (ITP): Preliminary Data from the Platelet Disorder Support Association (PDSA) Patient Registry

BACKGROUND AND AIMS Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder causing low platelet counts (PC) and an increased risk for bleeding. Some parents hesitate to vaccinate their children with ITP against SARS-CoV-2 fearing, based on data in adults, that it will trigger a PC decrease and exacerbate disease. We review how COVID-19 infections and vaccinations impact children and young adults with ITP in a small cohort.

METHODS Data was collected using the COVID-19 & ITP survey in the ITP Natural History Study Registry. As of June 23, 2022, 21 parents of children with pre-existing ITP (< 18 years of age) and 9 young adults with pre-existing ITP (ages 18-21 years) completed the survey. Data was analyzed with descriptive statistics and chi-squared tests.

RESULTS Most of the 30 participants were female (53%), under 18 (70%), and reported their diagnosis was primary ITP (90%) with no co-morbid conditions; 25% self-reported they were in remission, 50% had received ITP treatment within the last 6 months, and 1 patient reported having had a splenectomy.

Viral disease: Eleven participants (37%) were diagnosed with SARS-CoV-2: 5 (46%) reported their PC did not change, in 4 (36%) their PC increased, and 2 (18%) did not provide counts. Summary: no PC decreases and no bleeding during or after infection. Recovery to baseline was reported in two of four patients who had a PC change with recovery within one month; 2 did not report their PC. There were no hospitalizations or deaths, or reports. Six participants who tested positive had received treatment for their ITP within the last six months, however only one of 6 had received immuno- suppressants, (a corticosteroid and mycophenolate mofetil), the latter in addition to a thrombopoietin receptor agonist.

Vaccination impacts: 24/30 (72%) ITP patients reported receiving at least one vaccine dose at survey completion; 20/30 (61%) reported being fully vaccinated (2 doses): Pfizer (75%), Moderna (17%), and Johnson & Johnson (8%).

Following the first vaccine dose (D1), 22/24 participants reported their PC: increases were seen by 8/22 (36%), decreases by 5/22 (23%), and 9/22 (41%) had no change. Of the 13 with a PC change following D1, 67% returned to baseline within one month.

Of the 20 fully vaccinated participants, following dose two (D2), PC increases were reported by 2 (10%), PC decreases by 7 (35%) and 11 (55%) reported no change. A return to usual baseline occurred within 3 months in the 9 fully vaccinated individuals, in 6 within 4 weeks. One participant had been in remission for four years and then relapsed following D2 when their PC decreased by 30,000-50,000/µL.

Four out of 5 (80%) children who reported a PC decrease following D1 also experienced a PC decrease following D2. Only 1/8 (13%) reported a PC increase following both D1 and D2. The majority (7/9) of participants who reported their PC remained the same after D1 experienced the same response following D2. Total changes in PC following receipt of D1 vs D2 were not statistically significant (X² = 0.84, p = 0.36); however, there were notably more PC increases following D1 than D2 (X² = 4.01, p = 0.045).

Six participants had experienced a decrease in PC following a past non-COVID vaccine. Of these, five reported they were fully vaccinated for COVID-19, and reported they did not have a PC decrease following either D1 or D1.

De novo ITP was reported in 3 children/young adults following receipt of D1. They were not included in the study.

CONCLUSION These preliminary results in only 30 children nonetheless serve to reassure parents of children with ITP and young adults under age 21 years that the risk for platelet count decreases and worsening ITP due to either contracting the SARS-CoV-2 virus or receiving the COVID-19 vaccines appears to be quite low. In particular, even if the count decreases, it was almost always transient. Using the response to D1 is not reliable in predicting a PC change following D2. These findings should reduce vaccine hesitancy among ITP caregivers and young adults and encourage more to be vaccinated (and probably even boosted) whether or not they had problems with a previous vaccination.

MacWhirter - DiRaimo:Novartis: Consultancy. Kruse:Novartis: Consultancy. Bussel:Rallybio: Consultancy, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Other: Data and Safety Monitoring Board; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Rigel: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sobi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; UCB: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Data and Safety Monitoring Board; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees.