Anti-platelet factor 4 (anti-PF4) antibodies were identified as pathogenic antibodies for vaccine-induced immune thrombocytopenia and thrombosis (VITT) in subjects receiving ChAdOx1 nCoV-19 vaccinations. We performed a prospective cohort study to determine the prevalence of anti-PF4 and the effect of the ChAdOx1 nCoV-19 vaccine on anti-PF4 in healthy Thai subjects. Anti-PF4 antibodies were measured before and four weeks after receiving the first vaccination. Participants with detectable antibodies were scheduled for repeat anti-PF4 analysis at 12 weeks after the second vaccination. Of 396 participants, ten participants (2.53%; 95% confidence interval [CI], 1.22–4.59) were positive for anti-PF4 before receiving vaccinations. Twelve people (3.03%; 95% CI, 1.58–5.23) had detectable anti-PF4 after the first vaccination. There was no difference in the optical density (OD) values of anti-PF4 antibodies when comparisons were made between pre-vaccination and four weeks after the first vaccination (p = 0.0779). There was also no significant difference in OD values in participants with detectable antibodies. No subjects experienced thrombotic complications. Pain at the injection site was associated with an increased risk of being anti-PF4 positive at an odds ratio of 3.44 (95% CI, 1.06–11.18). To conclude, the prevalence of anti-PF4 was low in Thais and did not significantly change over time.

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Background: Cardiovascular events are the most serious complications for patients with myeloproliferative neoplasms (MPNs). There was limited data regarding arterial stiffness in these patients. Methods: This was a cross-sectional study aiming to determine the prevalence of arterial stiffness that was evaluated by cardio-ankle vascular index (CAVI) in patients with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). We defined arterial stiffness as a mean CAVI of 8.0 or more. We compared the prevalence of arterial stiffness in non-MPN patients with cardiovascular risk by matching age, sex, and Thai CV risk score. Results: A total of 80 patients were enrolled (PV, n = 50; ET, n = 24; PMF, n = 6) with median age of 63.5 years (IQR 50.9-76.1). The prevalence of arterial stiffness in patients with MPNs was 63.8%, and among patients with ET, PV, and PMF was 70.8%, 60.0%, 66.7%, respectively (p = 0.655). After matching, the prevalence of arterial stiffness was not statistically significant difference when compared to the non-MPN population with cardiovascular risk (65.2% vs 60.9%, P = 0.539). Conclusion The prevalence of arterial stiffness in patients with MPNs was 63.8% which was comparable to non-MPN patients with cardiovascular risk.

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