First large-scale US Covid-19 vaccine trial reaches target enrollment of 30,000 participants

Moderna, the first company to start US clinical trials of a Covid-19 vaccine, on Thursday finished enrolling all 30,000 of its participants.

All 30,000 have received their first shot, and most of them have also received the required second shot.

The company’s president says it’s now on track to apply to the US Food and Drug Administration for authorization to put the vaccine on the market in early December “if all the stars align.”

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Dr. Stephen Hoge, Moderna’s president, said enrolling 30,000 participants is “just a milestone – it’s not the mission.” Half of the participants received the vaccine and half received a placebo, or a shot of saline that does nothing. The participants receive a second shot four weeks later.

Moderna is one of four US Phase 3 trials of coronavirus vaccines, each involving tens of thousands of participants.

Moderna started its Phase 3 trial July 27, and Pfizer started its trial that evening. AstraZeneca started its US trial August 31 and paused it about a week later when a participant fell ill. Johnson & Johnson started its trial September 23 and paused it less than three weeks later for the same reason. Both of those pauses are still in effect.

Pfizer has said it could apply for emergency use authorization after the third week in November.

Hoge said three things needs to happen before Moderna applies to the FDA for emergency use authorization.

Of the 30,000 participants, 53 need to become sick with Covid-19. The company expects that to happen in the second half of November.

The second milestone is that of the 53 participants who become ill with Covid-19, at least 40 of them need to be participants who received the placebo. That would show the vaccine is 75% effective.

The third milestone is a requirement by the FDA to ensure that enough time has passed to see if participants develop side effects. The FDA rule is that at least eight weeks must pass after half the participants have received their second shot before a company can apply for emergency use authorization.

So far, 25,650 participants have received their second shot, and Hoge said Moderna expects to hit this safety milestone in the second half of November.

Thursday, Moderna also released the racial breakdown of its study participants. Of the 30,000 participants, 20% are Latino and 10% are Black. Those are higher than the percentages the company was achieving early in its trial, but still lower than the percentages sought by Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.