key: cord-0930315-svearwil authors: Noikongdee, Phichchapha; Police, Pornnapa; Phojanasenee, Tichayapa; Chantrathammachart, Pichika; Niparuck, Pimjai; Puavilai, Teeraya; Phuphuakrat, Angsana; Angchaisuksiri, Pantep; Boonyawat, Kochawan title: Prevalence of anti–platelet factor 4/polyanionic antibodies after COVID‐19 vaccination with ChAdOx1 nCoV‐19 and CoronaVac in Thais date: 2021-10-11 journal: Res Pract Thromb Haemost DOI: 10.1002/rth2.12600 sha: db86604d640b3af74501773750b6c197b046ac48 doc_id: 930315 cord_uid: svearwil INTRODUCTION: Vaccine‐induced thrombotic thrombocytopenia (VITT) has been reported after vaccination with the adenoviral vector coronavirus disease 2019 (COVID‐19) vaccine ChAdOx1 nCoV‐19 in European countries. To date, two cases of VITT have been reported in Thais after COVID‐19 vaccination. We determined the frequency of anti–platelet factor 4 (PF4)/polyanionic antibodies in the Thai population receiving the COVID‐19 vaccines. METHODS: We conducted a cross‐sectional study to evaluate the prevalence of anti‐PF4/polyanionic antibodies in health care workers who received COVID‐19 vaccination with ChAdOx1 nCoV‐19 or CoronaVac within 7 to 35 days. A control population who had not been vaccinated was also included. Anti‐PF4/polyanionic antibodies were detected using ELISA. Functional assay with platelet aggregation was performed for all positive anti‐PF4/polyanionic antibody ELISA tests. RESULTS: A total of 646 participants were included in the study; 221 received ChAdOx1 nCoV‐19, 232 received CoronaVac, and 193 participants were in the control group. The prevalence of anti‐PF4 antibodies was 2.3% (95% confidence interval [CI], 0.7‐5.2), 1.7% (95% CI, 0.5‐4.4) in the ChAdOx1 nCoV‐19 and CoronaVac groups, respectively. There was no positive test in the control group. None of the PF4/polyanionic positive sera induced platelet aggregation. CONCLUSION: We found a low prevalence of anti‐PF4 antibodies in Thais after vaccination with ChAdOx1 nCoV‐19 and CoronaVac. None of the antibodies were functional and lacked an association with VITT. • Anti-platelet factor 4 (PF4) is associated with vaccine-induced thrombotic thrombocytopenia (VITT). • Low-titer PF4 antibodies following ChAdOx1 nCoV-19 and CoronaVac vaccination are observed. • These PF4/polyanion antibodies do not activate platelets and lack an association with VITT. • The significance of these low-titer PF4 antibodies remains unknown. A cross-sectional study was conducted at Ramathibodi Hospital, a tertiary care academic hospital in Bangkok, Thailand. Adult health care workers who had received COVID-19 vaccination with either ChAdOx1 nCoV-19 or CoronaVac within 7 to 35 days were included in the study. Healthy volunteer participants who had not been vaccinated were also included as a control group. All participants gave written informed consent. Baseline characteristics including age and sex were recorded. The study protocol was approved by the Human Research Ethics Committee of the Faculty of Medicine at Ramathibodi Hospital, Mahidol University. Baseline characteristics were analyzed and presented with mean and standard deviation or median and interquartile range as appro- for 65.6%, 83.6%, and 29.5% in the ChAdOx1 nCoV-19, CoronaVac, and control groups, respectively. The median day (range) after first vaccination was 23 (18-27) and 18.5 (10-34), respectively (Table 1) The results of our study were comparable to a prior study from Norway 6 that reported a 1.2% prevalence of anti-PF4/polyanion antibodies after COVID-19 vaccination with ChAdOx1 nCoV-19. The anti-PF4/polyanion antibodies were also negative in all participants in the control group in that study. However, a study from Germany demonstrated a higher frequency of anti-PF4 antibodies among vaccinees receiving ChAdOx1 nCoV-19 (8.0%). 7 It also demonstrated seroconversion of anti-PF4 in two of six available samples, while preexisting antibodies were found in the other four available samples. These two studies used different PF4/polyanion ELISA assays. However, both studies also showed that ODs were mostly low (<1.0) and none of the PF4/polyanion ELISA-positive samples induced platelet activation. There has been no report of VITT after vaccination with CoronaVac, which is an inactivated virus vaccine. However, the prevalences of anti-PF4/polyanionic antibodies after vaccination with ChAdOx1 nCoV-19 and CoronaVac were similar in this study. Since the titer of all positive samples is low, its significance is unknown. The link between vaccination and antibody formation is unknown. The authors declare no conflicts of interest. P. Noikongdee, PP, and T. Phojanasenee recruited participants, performed the laboratory tests and ran the project. PP and KB performed the statistical analyses. PC, T. Puavilai, P. Niparuck, and AP collected the specimen. AP critically revised the manuscript. PA and KB designed the study and wrote the manuscript. Pantep Angchaisuksiri @PantepAng SARS-CoV-2 vaccines Thrombotic thrombocytopenia after ChAdOx1 nCov-19 vaccination Thrombosis and thrombocytopenia after ChAdOx1 nCoV-19 vaccination Pathologic antibodies to platelet factor 4 after ChAdOx1 nCoV-19 vaccination Adverse effect after COVID-19 vaccination in Thailand An observational study to identify the prevalence of thrombocytopenia and anti-PF4/ polyanion antibodies in Norwegian health care workers after COVID-19 vaccination Frequency of positive anti-PF4/polyanion antibody tests after COVID-19 vaccination with ChAdOx1 nCoV-19 and BNT162b2 Low prevalence of heparin-induced thrombocytopenia after cardiac surgery in Thai patients Allele frequency net database (AFND) 2020 update. How to cite this article: Noikongdee P, Police P Prevalence of anti-platelet factor 4/ polyanionic antibodies after COVID-19 vaccination with ChAdOx1 nCoV-19 and CoronaVac in Thais Anti-PF4/polyanionic antibodies were positive in five participants in the ChAdOx1 nCoV-19, and four participants in the CoronaVac group by ELISA. The highest OD was 0.9. OD of >0.3 indicates positive result. Black dots indicate OD after first-dose vaccination, and red diamonds indicate OD after second-dose vaccination. Gray shading indicates negative range. OD; optical density