MADISON, Wis. (SPECTRUM NEWS) -- On Tuesday, AstraZeneca voluntarily halted its Phase 3 COVID-19 trial because of one unexplained illness in the United Kingdom. 

 A representative for the drug manufacture says it along with an independent committee will investigate, but now question swirl over how common it is to put a top trial on hold.  

"This is the reason that all these pharmaceutical companies say research and development is such an expensive part of the process," Dr. Ken Perry, a Fellow of the American College of Emergency Physicians said about the concerning news.  

He says by the time a drug makes it to Phase 3, it only has a 1 in 3 or even 1 in 4 chance of making it through.

"You are really close, but in reality, the goal line is still ahead of you," Dr. Perry said. "You have to make sure that at that Phase 3 trial, you're now getting enough people involved in the trial that you can get the data back to make sure it's safe and make sure it's getting the outcome that you're looking for," he added.

Meanwhile, Dr. Perry says pausing a human trial is actually pretty common.

"This really is a take a couple steps forward reevaluate your where you are, take a step or two back and make sure that it is both safe and appropriate to go forward," he said.

Meanwhile, UW Madison researcher Thomas Friedrich believes AstraZeneca made the correct choice for safety, especially after UW Health was chosen as one of the dozen U.S. testing sites for the potential vaccine.

"I think the company is doing the right thing by pausing enrollment," Prof. Friedrich said. "It may be difficult to determine if this adverse event is truly associated with the vaccine or not. If you vaccinate enough people, someone is bound to have a health problem soon after vaccination, and it will take some careful investigation to determine whether the problem was caused by the vaccine, or whether it just happened by chance after the vaccine was given," he added.

Professor Friedrich says this is why the utmost care must be taken with this vaccine's study.

"This underscores the need to have a deliberate scientific process to carefully vet the safety and efficacy of vaccines. Bottom line is that this pause is giving the scientific process a chance to work, and I don’t think we have reason to be concerned yet about the future of COVID vaccines as a whole. I expect we are still on track to have one or more safe and effective vaccines available, though they will probably not be widely available until well into 2021.

AstraZeneca did not say how soon the drugmaker might re-start the trial, but did say they are expediting the review to quote minimize any potential impact on the trial timeline.