Unusual arm vein thrombosis after the Moderna (mRNA-1273) COVID-19 vaccination-a case report

Since 2019, all over the world is still suffering from managing never-experienced pandemic era of coronavirus-2019 (COVID-19). Prompt development and administration of vaccines contributed lowering severity of the disease, but adverse events related to vaccination were also reported. Exact association between each adverse conditions and vaccination or COVID-19 infection are being investigated.

A 44-year-old Asian male developed right upper arm diffuse swelling 4 days after receiving the third dose of messenger ribonucleic acid (mRNA)-1273 COVID-19 vaccine in his left deltoid muscle. He was previously healthy, but has history of COVID-19 infection 4 months before the third dose vaccination. Venous duplex ultrasound revealed acute thrombosis in the right cephalic arch, axillary vein, and subclavian vein. There were no abnormal laboratory test results. After 3 months of anticoagulation therapy, arm vein thrombosis was completely resolved upon follow-up duplex ultrasonography.

Although, positive COVID-19 polymerase chain reaction (PCR) history might be associated with potential cause of this unusual arm vein thrombosis, we postulate that a possible cause may be secondary to his third dose of mRNA-1273 vaccine given the onset and no prior medical comorbidities. Since the previous studies was mostly done based on mRNA vaccines of other manufacturers rather than Moderna, exact thrombosis mechanism of this case was not established yet. Contralateral arm vein thrombosis is unique to report, and future comprehensive studies are needed.