By Peter Loftus and Jared S. Hopkins 

Two of the most advanced experimental coronavirus vaccines entered the pivotal phase of their studies on Monday, with the first subjects receiving doses of Moderna Inc.'s vaccine and Pfizer Inc. readying to inject participants in its trial.

Researchers evaluating the vaccines plan to enroll 30,000 people in separate last-stage, or phase 3 trials, results of which will determine whether the vaccines protect against symptomatic Covid-19, and whether they should be cleared for widespread use.

Moderna's two-dose vaccine will be administered at sites across the U.S. The Cambridge, Mass., company also received an additional commitment of up to $472 million from the federal government to support the large study, on top of the $483 million in funding earlier in the year for development, testing and preparations to manufacture at large scale.

Moderna, which codesigned the vaccine with the National Institute of Allergy and Infectious Diseases, previously reported promising results of the first study of the vaccine, showing it induced immune responses and was generally safe in a small number of people.

The new phase 3 trial, titled Cove, is being conducted at nearly 90 sites in the U.S., including many in states such as Texas where the virus has surged in recent weeks.

Pfizer's trial, which will begin in the U.S. but expand overseas to include about 120 sites, will evaluate a vaccine developed with partner BioNTech SE. The shot is one of four candidates the companies evaluated.

As vaccines proceed through the final stages of testing, countries are jockeying to secure enough shots, should they prove safe and effective, and the supplies to transport them.

Last week, the U.S. agreed to pay Pfizer and BioNTech nearly $2 billion to secure 100 million doses of their experimental Covid-19 vaccine to provide to U.S. patients free of charge. Pfizer is targeting October to file for regulatory approval or an emergency use authorization.

No vaccine has proven to work safely against the coronavirus. Many vaccines developed to target other pathogens have failed in testing, including in phase 3 trials.

U.S. officials said Monday it was the fastest time from the design of a new vaccine to the start of phase 3 testing in the U.S. NIAID researchers helped design the vaccine, code-named mRNA-1273, in January after the genetic code of the virus was posted to a public database.

"Yes, we're going fast, but no, we are not going to compromise safety or efficacy," National Institutes of Health Director Francis Collins said on a conference call with reporters Monday. NIAID is part of the NIH.

The start of the pivotal Moderna vaccine trial is the latest sign that the most advanced coronavirus vaccine candidates are moving into the final stages of testing, and could be ready for wider use before year's end if results are positive.

A vaccine co-developed by the University of Oxford and AstraZeneca PLC started a large study in May in the U.K., and is due to enter a phase 3 study in the U.S. in August.

Another company expected to be a major player in the vaccine hunt, Johnson & Johnson, started dosing participants in the first U.S. human study of its experimental shot Monday. A larger, phase 3 study of J&J's vaccine may start in September.

Moderna hopes its large study, which is being conducted in collaboration with the NIH, will yield positive results and possible vaccine availability in the fall, with J&J aiming for similar milestones by early 2021.

In the new Moderna vaccine study, about half of the adult volunteers will receive two shots of the vaccine four weeks apart, while the other half will get two doses of a placebo. Starting two weeks after the second dose, researchers will track whether the rate of symptomatic Covid-19 disease in the vaccinated group is lower than in unvaccinated people.

NIAID Director Anthony Fauci said researchers may learn in November or December whether the Moderna vaccine works, but the answer could come sooner, depending on infection rates in the places where the study is being conducted.

Moderna has been manufacturing doses even before getting an answer on efficacy, but if it gets a green light from the government for wider user, it is unlikely there will be enough doses for all Americans right away.

Chief Executive Stéphane Bancel said there could be enough doses initially for "millions and millions" of people, which could be prioritized for at-risk groups like health-care workers.

The NIH and the Centers for Disease Control and Prevention have asked a National Academy of Medicine committee to come up with a plan for equitable allocation of any effective Covid-19 vaccines.

Moderna expects a wider rollout of the vaccine next year if the study is positive. It says it is on track to deliver about 500 million doses a year, and possibly up to one billion doses, starting in 2021.

Moderna shares rose 9% to $79.91 in trading Monday.

Write to Peter Loftus at peter.loftus@wsj.com and Jared S. Hopkins at jared.hopkins@wsj.com

 

(END) Dow Jones Newswires

July 27, 2020 18:38 ET (22:38 GMT)

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