By Jenny Strasburg and Joseph Walker

AstraZeneca PLC released more pivotal-trial data for its Covid-19 vaccine, saying the shot was 76% effective at preventing Covid-19 with symptoms in a fuller analysis of study results than the company had earlier provided.

AstraZeneca said its latest figures on the vaccine's efficacy was based on an analysis of 190 cases of symptomatic Covid-19 in the trial, 49 more cases than the company had analyzed earlier.

Despite the additional cases, the vaccine's performance was in line with what AstraZeneca had first reported.

The London-based drugmaker had drawn fire earlier this week after it had provided preliminary data from the trial indicating its vaccine was 79% effective in 141 subjects.

An independent study-monitoring board said the data were out of date, prompting the U.S. National Institute of Allergy and Infectious Diseases to issue an unusual statement raising the experts' concerns.

The tempest added to the clouds that have hovered over the shot, which AstraZeneca developed in partnership with the University of Oxford.

Its rollout has been marred by a series of missteps including how the partners communicated earlier U.K. trial results. They presented a confusing array of dosing sizes and schedules, a wide range of efficacy results and few elderly trial subjects.

In Europe, AstraZeneca has fallen far short of supply targets, prompting fierce condemnation from European officials and threats of bans on exports of vaccines as the bloc tries to secure doses amid rising infections.

Also, more than a dozen European countries had halted use of the vaccine after blood-clotting reports. Most of the countries have resumed giving the shots, after an investigation didn't find a link between the vaccine and the clotting events and reiterated that the vaccine's benefits outweighed any potential risks.

Early this week, NIAID Director Anthony Fauci described AstraZeneca's latest problem as an "unforced error."

Pfizer Inc. Chief Executive Albert Bourla expressed concern at The Wall Street Journal Health Forum on Tuesday that the imbroglio could encourage hesitancy in taking Covid-19 vaccines generally.

AstraZeneca's latest results, released late Wednesday night U.S. time, were largely consistent with preliminary findings reported Monday, based on trial data as of Feb. 17.

Aside from finding the vaccine 79% effective, the preliminary results indicated that the vaccine was even more effective in study subjects ages 65 years and older and that the shot was safe.

The late-stage, or Phase 3, trial had 32,449 subjects in the U.S., Peru and Chile. About 20% of them were 65 years or older.

The fuller data showed the vaccine to be 85% effective in the older age group. Older adults are considered more vulnerable to serious Covid-19, making them a high-priority group in vaccinations globally.

Though AstraZeneca's latest release involved more cases, the company's analysis might still be incomplete. AstraZeneca said it was reviewing an additional 14 cases to see if they should be added to the final tally.

In both analyses, the vaccine was found to provide 100% protection against severe disease and hospitalization, though the numbers of such serious cases were small.

In the fuller findings, eight study volunteers developed severe disease, all of them in the group of trial volunteers who had received a placebo, not the vaccine, according to AstraZeneca.

Health experts say the shot's efficacy is strong. Vaccines from Moderna Inc. and Pfizer's partnership with BioNTech SE were 94% or more effective in their trials, while Johnson & Johnson's was 66%.

The United Kingdom and certain other countries have already been giving AstraZeneca's shot to people, and many other countries have been counting on it to move past the pandemic.

The British-Swedish drugmaker has pledged to deliver 3 billion doses this year without profiting from the shot.

AstraZeneca said it would submit the findings for peer review and publication in coming weeks and would request authorization of the vaccine from the U.S. Food and Drug Administration.

Executives said Monday they planned to submit findings to the FDA by mid-April.

"We look forward to filing our regulatory submission for Emergency Use Authorization in the U.S. and preparing for the rollout of millions of doses across America," AstraZeneca's Mene Pangalos, executive vice president for biopharmaceuticals research and development, said in a statement.

Write to Jenny Strasburg at jenny.strasburg@wsj.com and Joseph Walker at joseph.walker@wsj.com

(END) Dow Jones Newswires

03-24-21 2302ET