The hunt for a safe and effective vaccine that would help the world contain and progress from the coronavirus pandemic started as early as January when the SARS-CoV-2 virus's gene were sequenced by multiple global researchers. From there, hundreds of companies and scientific institutes have pledged to rapidly develop a vaccine in a shortened timeline that many experts had warned is unprecedented due to most vaccines for other infectious diseases taking years to be safely developed. AstraZeneca (AZN  ), in partnership with Oxford University, is one of those companies, setting a deadline to have a coronavirus vaccine ready for regulatory approval by the end of the year.

However, AstraZeneca's large-scale clinical trial has paused on Tuesday after a participant in the Phase III study developed a severe adverse reaction that may or may not be linked to the company's experimental vaccine. According to the New York Times, the study participant has experienced symptoms that are consistent with a condition known as transverse myelitis, or inflammation of the spinal cord.

While the trial's suspension allows for independent researchers to trace the participant's medical history, as well as whether or not the symptoms began once AstraZeneca's vaccine was administered, this was not the first time the company's vaccine trials were halted due to severe neurological symptoms. Another participant back in July had developed symptoms of transverse myelitis, but the vaccine candidate's trial resumed after the they were diagnosed with an "unrelated neurological illness," according to the New York Times.

Transverse myelitis is a rare disease, only affecting about 1,400 people each year in the United States, according to the National Institutes of Health.

While the participant in the AstraZeneca trial may not have the disease, the investigation into the manner has no clear timeline which could lead to a setback for the drugmaker. The trial's halt can also have another unwanted affect: it could lead more people to not trust a coronavirus vaccine once one is made available for public use.

According to a recent USA Today/Suffolk Poll of 1,000 Americans, two-thirds of those surveyed would either not take a coronavirus vaccine until others have tried it or not take one at all. Less than one-third of the survey population said that they would take a coronavirus vaccine as soon as it was available.

Pfizer (PFE  ) CEO Albert Bourla said in an interview with NBC's "TODAY" Tuesday that individual's who do not take a coronavirus vaccine once it is made available will become a "weak link" that will allow the pandemic to continue. Vaccines work efficiently when most of a population uses them, building a herd immunity against the virus so that it cannot spread to the more vulnerable.

Bourla stated that while he understands the public's concern over the rapid development of the front-running coronavirus vaccines, those who decide not to take one "will affect the lives of others because if they don't vaccinate, they will become the weak link that will allow this virus to replicate." That replication will render the vaccine useless.