A volunteer for a COVID-19 vaccine trial in the United States has suffered an adverse reaction, but is remaining "cautiously optimistic" about the potential cure.
Ian Haydon, 29, from Seattle, Washington has been taking part in the trial by Moderna Therapeutics to find a cure for coronavirus since early May.
He'd signed up for the study after a colleague sent him a link and was selected from thousands of applicants.
Haydon received his first dose of vaccine on April 8, but after experiencing a sore arm the first time was "slightly nervous" before his second injection, Stat News reported.
"Then, 12 hours after getting the second injection, I suddenly had severe chills. I decided to go to sleep but woke up in the middle of the night with a fever that was over 103 degrees. I also found I was nauseous, fatigued and had quite a headache," Haydon told TODAY.
After being admitted to urgent care, Haydon was given painkillers and went home, despite being offered hospital care.
The next morning Haydon was vomiting and fainted, but eventually recouped.
The university communications manager, who has been conducting interviews over the last couple of weeks recording his experiences in the study, initially hid his reaction from the media.
In a series of tweets he said he didn't want to trigger any anti-vax people as he believes there are still positives to come out of the study.
"I understand that sharing the story, it’s going to be frightening to some people," he told Stat News.
"I hope that it doesn’t fuel any sort of general antagonism towards vaccines in general or towards even this vaccine."
He says he "doesn't regret" the decision to enrol in the study and the point of it is to figure out the side effects.
"As we rush to get a vaccine developed as quickly as possible, the reality of vaccine development is that it can only be rushed so much and the trial still needs to take place," Haydon said.
"They have to move at the speed they move at. And stories like what happened to me, they matter because they shape the approval process."
On Wednesday he took to Twitter to say the company would no longer be testing the highest dose of the virus after at least two other people also experienced severe reactions.
He also admitted while feeling it was sickest he had ever felt, it still wasn't as bad as what some people were going through during the pandemic.
"The symptoms I experienced weren't life-threatening. They're over, and I'm back to marathon training.
"Vaccines are the single most important medicines we have. It's important to test them carefully - which is what's happening here. I remain cautiously optimistic...
"I'll also note that what I went through pales in comparison to being hospitalised with COVID-19. Or to the pain of losing a loved one to the pandemic."
There are currently over 1.69 million confirmed cases of coronavirus in the United States and 100,000 people have died, according to tracking data from John Hopkins University.