The company said its shot was 76 percent effective at preventing Covid-19, a hair lower than the number it announced earlier this week.
AstraZeneca reiterated on Wednesday that its Covid-19 vaccine was very effective at preventing the disease, based on more recent data than was included when the company announced the interim results of its U.S. clinical trial on Monday.
The company said in a news release that its vaccine was 76 percent effective at preventing Covid-19. That is slightly lower than the number that the company announced earlier this week.
The new results strengthen the scientific case for the embattled vaccine. But they may not repair the damage to AstraZeneca’s credibility after U.S. health officials and independent monitors issued an extraordinary rebuke of the company for not counting some Covid-19 cases when it announced its initial findings this week.
In a news release on Wednesday, the company said complete results from its 32,000-person study showed that its vaccine was 76 percent effective. On Monday, the company had said the vaccine appeared to be 79 percent effective, based on an interim look at 141 Covid-19 cases that had turned up among volunteers before Feb. 17. The latest finding was based on 190 trial participants who had gotten sick with Covid-19.
AstraZeneca said on Wednesday that the vaccine was 100 percent effective in preventing severe disease and 85 percent effective in preventing Covid-19 in people over age 65.
When it unveiled its interim results on Monday, AstraZeneca ignored dozens of recently confirmed Covid-19 cases that had cropped up in trial volunteers before mid-February.
In a letter to the company and federal officials, the independent monitoring board that was helping oversee the clinical trial issued an unusual reprimand of AstraZeneca for appearing to cherry-pick data to make its vaccine appear more effective.
“Decisions like this are what erode public trust in the scientific process,” the letter said. The members of the monitoring board wrote that their statistical modeling had found that the vaccine might have a lower efficacy rate — between 69 and 74 percent — if the Covid-19 cases in question were included in the analysis.
The National Institute of Allergy and Infectious Diseases later disclosed the panel’s concerns via a public statement.
It was not clear why the monitoring board’s projection turned out to be lower than the figure in AstraZeneca’s complete results. The latest results could still change because there are still 14 possible Covid-19 cases that AstraZeneca representatives have not yet classified as actual cases.
Until they received the monitoring board’s letter, AstraZeneca executives weren’t aware that the panel expected them to include those cases in the results disclosed in their news release, according to a person familiar with the executives’ thinking.
Vaccine experts said the brushback from federal officials appeared to reflect high levels of distrust between American regulators and AstraZeneca. Some worried that the episode could damage public confidence not only in AstraZeneca’s vaccine, but in all coronavirus vaccines.
“There seems to be a breakdown in relations between the D.S.M.B. and the company, which is probably due to a variety of factors and is sad,” said Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, referring to the independent monitoring board. “This vaccine is so important for global health and the disputes do not promote global health.”
The dust-up over AstraZeneca’s U.S. trial results followed a safety scare in Europe that prompted more than a dozen countries to temporarily suspend use of the vaccine. Regulators in Europe said last week that a review had found the shot to be safe after a small number of people who had recently been inoculated developed blood clots and abnormal bleeding. The U.S. trial did not turn up any signs of such safety problems.
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