Makers of two of the leading coronavirus vaccine candidates disclosed detailed information about their pivotal late-stage clinical trials and how they plan to gauge their shots' safety and effectiveness.

The moves by Moderna Inc., as well as Pfizer Inc. and partner BioNTech SE, follow increasing worry that the effort to develop a COVID-19 vaccine is becoming politicized, and that an inoculation could be rushed to market before it is proven safe and effective.

Moderna released its plan ahead of an early Thursday morning investor meeting. It also said its trial has now enrolled 25,296 of an expected 30,000 volunteers, and more than 10,000 have received two doses of the vaccine. Hours later, Pfizer Inc. followed Moderna's move, releasing its detailed trial plan, a 137-page document that details under what circumstances the trial could generate early efficacy results.

While the broad outlines of major drug trials are available on a U.S. government website, details of how and when monitoring boards overseeing the trials plan to analyze data are often kept confidential by pharmaceutical companies.

However, the unprecedented push to get a vaccine to market quickly has increased interest in those details. The analysis of findings and what the rules are for stopping a trial if there are encouraging early signals could determine how quickly a shot receives emergency authorization from U.S. regulators.

Moderna decided to release its full trial plan to create public confidence that it is doing everything it can to ensure a vaccine is safe and effective, said Chief Executive Officer Stephane Bancel.

"We have been working nine months to try to stop this virus by getting a vaccine to market," Bancel said in an interview. "We want to make sure the general public has trust in vaccines by being transparent."

Bancel said the most likely scenario was that Moderna's vaccine could generate preliminary efficacy data in November. It is "technically possible" for Moderna to get results in October, but this is unlikely, he said.

Under the Moderna plan, a data monitoring board will take a preliminary look at the efficacy results after 53 participants have contracted the coronavirus, and again after 106 cases are reached. The final analysis will occur after 151 cases, according to slides from the investor meeting.

Moderna's plan is more conservative than the 32-case benchmark being used by Pfizer Inc. for its first preliminary analysis of the COVID-19 vaccine it's developing with partner BioNTech SE. Pfizer has said conclusive efficacy results are likely by the end of October. The company didn't immediately respond to a request for comment early in the day.

According to a slide being presented at the meeting, Moderna's trial is only likely to generate clear positive results at the first analysis if it turns out to be very highly effective, reducing COVID-19 cases by 74% or more.

If the vaccine turns out to be a more modest 60% effective, the trial might have to proceed to the final efficacy readout in order to generate clear results, according to the 135-page trial protocol.

Bancel said "it is extremely unlikely" everyone in the country could get vaccinated by the end of the first quarter of 2021, as a Trump administration official suggested on Wednesday. All three of the most likely initial vaccines are based on newer technologies, which means that the companies have had to create new manufacturing capacity, he said.

There will likely only be enough vaccines approved for every American who wants a shot by the second half of next year, according to Bancel.

Unlike an AstraZeneca PLC trial that has been put on hold twice to investigate possible neurological adverse events, Moderna's trial hasn't had any pauses to probe potential safety problems, Bancel said.

The AstraZeneca vaccine trial in the U.K. resumed after a safety review was completed, while another AstraZeneca trial in the U.S. remains on hold. Documents sent to participants in the U.K. say the symptoms probably weren't related to the AstraZeneca shot.

In an email, an AstraZeneca spokeswoman said it had "no update as of right now" on its U.S. trial design beyond details already available in the U.S. database, clinicaltrials.gov.

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