Two major large-scale clinical trials testing the safety and effectiveness of their respective coronavirus drugs have paused participant enrollments over safety concerns. The two studies--conducted by Johnson & Johnson (JNJ  ) and Eli Lilly and Company (LLY  )--will now be reviewed independent regulators who will investigate the concerns raised before allowing the trials to continue, a process that has an indefinite timeline.

Johnson & Johnson's late-stage study of its one-shot potential coronavirus vaccine was the first to halt its research late Monday night, with the drugmaker pausing the trial due to "an unexplained illness in a study participant."

The company has declined to provide additional information on the patient's condition due to privacy concerns. Johnson & Johnson stated that researchers are "learning more about this participant's illness, and it's important to have all the facts before we share additional information."

The company stated that the participant's illness will be reviewed and evaluated by an independent Data Safety Monitoring Board (D.S.M.B.), as well as the company's internal researchers and safety physicians.

While the Johnson & Johnson notes that these types of trial pauses are not uncommon, with some only lasting a few days, it is still unclear how long the investigation will last.

Eli Lilly's clinical trial of its monoclonal antibody treatment was paused on Tuesday, with U.S. regulators raising undisclosed safety concerns over the government-sponsored trial. The late-stage ACTIV-3 trial began back in August and sought to compare patients who received the company's antibody drug alongside Gilead Sciences's (GILD  ) remdesivir with those who were only treated with remdesivir.

"Out of an abundance of caution, the ACTIV-3 independent data safety monitoring board (D.S.M.B.) has recommended a pause in enrollment," Lilly spokesperson Molly McCully said in an emailed statement to Reuters. "Lilly is supportive of the decision by the independent D.S.M.B. to cautiously ensure the safety of the patients participating in this study."

Eli Lilly has recently submitted a request for an emergency use authorization (E.U.A.) from the U.S. Food and Drug Administration (F.D.A.) for use of the experimental drug in patients with mild-to-moderate COVID-19 infection. However, F.D.A. inspectors have voiced concerns over quality control at the pharmaceutical company's manufacturing factory that is producing the drug, according to Reuters sources. That investigation could result in the rejection of the company's request for an E.U.A. as well as harm the overall approval of the drug.

For now, the two trials will need to wait for regulatory approval to continue. The U.S. clinical trial halt for AstraZeneca's (AZN  ) potential coronavirus vaccine is the only timeline that is comparable to these situations, and that trial has been put on hold by the F.D.A. for over a month.

Johnson & Johnson's Chief Financial Officer Joseph Wolk told CNBC's "Squawk Box" on Tuesday that clinical trial pauses should "reassure" the public that the drugmaker is upholding high scientific, ethical and safety standards, especially when in comes to the sensitive manner of the development of a coronavirus treatment or vaccine.