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March 25, 2021

AstraZeneca says new analysis confirms its COVID-19 vaccine is effective

Following a rebuke from U.S. health officials, the British drugmaker released updating data showing its coronavirus shot is 76% effective

Prevention Vaccines
AstraZeneca vaccine findings Rafael Henrique/SOPA Images/Sipa USA

An updated analysis released by AstraZeneca shows its COVID-19 vaccine is 76% effective, a slight drop from the 79% rating the company touted Monday.

AstraZeneca updated the efficacy rating of its COVID-19 vaccine late Wednesday following a public scuffle with U.S. health officials who questioned the accuracy of its initial rating. 

A new analysis of AstraZeneca's U.S.-based clinical trial shows the vaccine is 76% effective at preventing symptomatic COVID-19 cases — a small drop from the 79% efficacy rate the company touted in a press release Monday.

The updated analysis included 190 symptomatic cases from the 32,449-person trial. The British drugmaker had included 141 cases in an interim analysis, released Monday, that covered data through Feb. 17. There are another 14 possible or probable cases that researchers want to double-check before including, STAT reported

The update again found the vaccine was 100% effective at preventing hospitalization and death from the coronavirus. Its efficacy rating for people ages 65 and older increased to 85% effective, up from 80% in the interim analysis. 

AstraZeneca, which collaborated with Oxford University to develop the vaccine, evoked confidence in the new results. 

"The primary analysis is consistent with our previously released interim analysis, and confirms that our COVID-19 vaccine is highly effective in adults, including those aged 65 yers and over," Executive Vice President Mene Pangalos said. "We look forward to filling our regulatory submission for emergency use authorization in the U.S. and preparing for the rollout of millions of doses across America."

The updated analysis was released after the National Institute of Allergy and Infectious Diseases issued a statement late Monday night suggesting the interim analysis included "outdated data" and provided "an incomplete view" of the vaccine's efficacy. 

In a letter to AstraZeneca, the Data and Safety Monitoring Board reportedly suggested the vaccine's efficacy rate could be between 69% and 74% effective, based on its own data analysis.

The updated analysis indeed included an overall efficacy rating within that range, though it was only slightly below the rating released Monday. 

Some health experts fear AstraZeneca's rebuke may have added to public concern regarding the vaccine. This could be worrisome since their shots are being distributed in 89 countries, more than any other coronavirus vaccine so far.

"This vaccine is so important for global health and the disputes do not promote global health," Stephen Evans, a professor at the London School of Hygiene and Tropical Medicine, told the New York Times

The disagreement came on the heels of a small number of recipients developing blood clots. The safety concerns prompted 16 countries to temporarily suspend the vaccine's use, but an emergency review by the European Medicines Agency found the blood clots were not connected to the shot. 

AstraZeneca's new findings still place it well above a 50% efficacy rate the U.S. Food and Drug Administration's bar for authorizing coronavirus vaccines. 

"At the end of the day, the FDA looks at the data, not the press releases," Dr. Jesse Goodman, a former chief scientist for the FDA, told Vox. "Looking at that data and doing their own analysis is what’s going to determine whether this vaccine gets an EUA, whether the benefits outweigh the risk." 

If authorized by the FDA, AstraZeneca would become the fourth COVID-19 vaccine available in the United States, along with shots developed by Moderna, Pfizer and Johnson & Johnson. 


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