A 49-year-old man who had the Moderna COVID-19 vaccine said he developed blood clots he feared would kill him, the MailOnline reported, while scientists have yet to provide a solid link between the new COVID-19 vaccines and blood clots.

Jeff Johnson’s claims have dragged the Massachusetts-based firm into an ongoing health scare that has already engulfed rival vaccine manufacturers AstraZeneca and Johnson & Johnson.

KDVR reported that Johnson, of Brighton, ended up in the emergency room after experiencing swelling and pain in his left leg. He was diagnosed with deep vein thrombosis (DVT), which is when a clot forms in a vein deep in the body such as in the thigh or lower leg.

Although these blood clots differ from the ones seen in patients who get the Johnson & Johnson vaccine, the man said he was scared he was going to die.

Johnson told KDVR he received the Moderna vaccine at the Salud Family Health Centers in Brighton, where he resides.

There were no issues until about 1 week later when he started feeling pain, swelling and tenderness in his left leg.

“I was concerned, naturally. I know blood clots are bad and I was afraid to die,” Johnson told the station.

When he went to the emergency room, doctors found 2 blood clots in his left leg, and he was told he had DVT.

Deep vein thrombosis happens when a blood clot forms in one or more of the deep veins in the body, typically the legs.

The cumulative chance of developing DVT over the course of a lifetime ranges from 2% to 5% and the chances of dying are less than 0.01%.

Johnson told KDVR that his doctor said the clots could have been caused by the Moderna jab, but there is no evidence. The man also noted that he became more concerned after he heard about clotting issues from the J&J vaccine.

Nonetheless, the clots associated with the J&J dose are different and are called cerebral venous sinus thrombosis (CVST).

CVST is a rare type of blood clot that blocks the brain’s sinus channels of draining blood, which can cause hemorrhages.

So far, 9 patients – 2 in clinical trials and 7 after the vaccine was approved – developed the clot, of which 1 died and 2 are in critical condition.

It led the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) to recommend on Tuesday that rollout of the J&J vaccine be paused until additional data can be collected.

Dr Pradeep Dhar, Vice President of Medical Services at Salud, where Johnson got his jab, told KDVR that CVST has not been associated with the Moderna vaccine.

He added that he has only seen 3 reports of people who developed blood clots like the ones Johnson experienced after vaccination out of at least 18 million appointments, and recommends everyone be immunized.

“The risk of getting a COVID infection and complications is way higher than the risk of having a clot with any vaccination,” Dhar said.