Moderna (NASDAQ:MRNA) continues to make progress enrolling patients in the phase 3 clinical trial testing its coronavirus vaccine, mRNA-1273. In its weekly update, the biotech said 21,411 patients were enrolled in the study. With a target of approximately 30,000 participants, the 71% enrollment in the study is up substantially from last week, when the company reported enrollment of 17,458 participants, or 58% of the targeted enrollment.

The week-over-week enrollment growth is especially impressive considering Moderna has said it's slowed enrollment slightly in order to increase the number of minorities that are enrolled in the study. People of different races can react differently to some drugs and vaccines, so it's important for the clinical trial to test the vaccine on a diverse population.

Hand with a syringe and a shoulder

Image source: Getty Images.

Moderna is neck and neck with Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX), which launched their phase 3 clinical trial at a similar time. Pfizer's most recent update on Monday said the duo had enrolled 20,006, or 66% of their similarly sized clinical trial. On Friday, Pfizer pointed out that 6,000 participants had received a second dose of the vaccine.

While completing enrollment in the clinical trials is essential for determining safety, the pace of enrollment is actually more important for efficacy because the companies can't start measuring whether the vaccine protects people until the booster shot is given three to four weeks after the initial shot. Participants enrolled early in the study will receive their second dose earlier and can help determine whether the full course of treatment helps prevent COVID-19 compared to two placebo shots.

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