After reviewing the adverse event that caused AstraZeneca (AZN -0.75%) to pause the clinical trials of its coronavirus vaccine, AZD1222, an independent review determined there's nothing to worry about.

Or at the very least, there's not enough evidence to determine whether there is something to worry about.

"After independent review, these illnesses were either considered unlikely to be associated with the vaccine or there was insufficient evidence to say for certain that the illnesses were or were not related to the vaccine," the clinical trial organizers for the phase 2/3 U.K. clinical trial wrote in the participant-information sheet, which was updated on Friday.

Gloved hands of a medical professional holding a needle near a patient's shoulder.

Image source: Getty Images.

The volunteers developed "unexplained neurological symptoms including changed sensation or limb weakness," which is a little more descriptive than simply calling it an "unexplained illness," as AstraZeneca did when it acknowledged that the clinical trials had been paused last week.

The U.K. clinical trials testing AZD1222 have restarted, but the 30,000-participant U.S.-based clinical trial remains on hold while the drugmaker waits for the monitoring committee for that study to sign off on restarting the study.

During its investor-day presentation yesterday, Pfizer (PFE -1.82%) said that there hadn't been any pauses in the clinical trials of its coronavirus vaccine, BNT162b2, which it is developing with BioNTech (BNTX -0.61%). Pfizer continuously monitors the safety data, and an independent data-monitoring committee (DMC) reviews the data weekly. Pfizer isn't privy to whether adverse events are in patients given the active vaccine or placebo, but the DMC gets unblinded data, so they can eliminate adverse events in patients receiving placebo as obviously not caused by the active vaccine.