What happened

Shares of Moderna (NASDAQ:MRNA) climbed 4.7% on Wednesday after a rival drugmaker's COVID-19 vaccine trial was placed on hold due to safety concerns.

So what

AstraZeneca (NASDAQ:AZN) paused its phase 3 clinical trial for its coronavirus vaccine candidate, labeled AZD1222, after a participant suffered an unexplained illness. An independent committee will review the safety data before the trial is allowed to resume. "We will be guided by this committee as to when the trials could restart, so that we can continue our work at the earliest opportunity to provide this vaccine broadly, equitably, and at no profit during this pandemic," AstraZeneca CEO Pascal Soriot said in a press release. 

A person is pointing to a chart that rises, then falls, then rises again.

Moderna's stock rallied on Wednesday. Image source: Getty Images.

Although AstraZeneca noted that a pause of this nature is a rather common occurrence during clinical trials, investors took the news as a sign that Moderna may not be as far behind its larger rival as some feared.

Now what 

While being first to market would certainly have its advantages, the outcome of the race for a coronavirus vaccine will ultimately be determined by which drug proves most effective at preventing COVID-19 with the fewest number of negative side effects. It's far too soon to call a winner in that regard -- and Moderna is certainly still in the running.

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