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Revised U.S. Trials Numbers Show AstraZeneca Vaccine Is 76% Effective Against Symptomatic Covid-19

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AstraZeneca on Wednesday released updated numbers from its large scale U.S. Phase III trials which show its Covid-19 vaccine is 76% effective against symptomatic disease—down from a previously claimed 79% efficacy—a day after the drugmaker was pulled up by U.S. health officials for including ‘outdated information’ in its original results.

Key Facts

In a press release, AstraZeneca once again reiterated its vaccine is 100% effective in preventing severe disease and hospitalization, showing the widely used shot offers robust protection to its recipients.

The company also revised its efficacy number for people above the age of 65, noting it was 85% effective in preventing symptomatic disease, which is higher than the previously stated 80% effectiveness.

The updated phase III trial numbers—which featured 32,449 participants mostly from the U.S. but also included some participants from Chile and Peru—recorded 190 symptomatic cases of COVID-19 among participants, up from 141 cases reported on Monday.

Two thirds of the participants received the vaccine—which was administered in two doses at a four-week interval—while the rest received a placebo shot.

Eight cases of severe COVID-19 observed in the trial, with all of those cases occurring in the placebo group.

The company still plans to submit the final analysis of the trial to the U.S. Food and Drug Administration (FDA) for emergency use authorization in the coming weeks.

What We Don’t Know

Citing a memo sent to the company and U.S. government officials, Washington Post reported on Tuesday the independent experts monitoring the trials had pegged the vaccine’s effectiveness between 69 and 75%, which is still slightly lower than the number AstraZeneca has claimed in its latest release. It is unclear why this is the case, however, AstraZeneca notes in its release that there are 14 additional possible or probable Covid-19 cases yet to be adjudicated, which may cause the final numbers to “fluctuate slightly.”

Crucial Quote

“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 years and over,” Mene Pangalos, the company’s executive vice president for BioPharmaceuticals R&D said.

Key Background

Wednesday’s revised numbers come after an unprecedented rebuke against the company’s previous announcement from the National Institute of Allergy and Infectious Diseases (NIAID) early on Tuesday. Less than a day after AstraZeneca claimed that the U.S. trials showed a 79% effectiveness against symptomatic Covid-19 for its vaccine, the NIAID put out a release expressing “concern” about the data. According to the NIAID, the Data and Safety Monitoring Board (DSMB)—the independent group of experts which monitored the trial—claimed that AstraZeneca may have included outdated information in its announcement, which may have provided an incomplete view of the vaccine’s effectiveness. Based on the updated data, the concern seems to have stemmed from AstraZeneca’s decision to exclude 49 symptomatic cases which it has now reported. In response to NIAID’s rebuke, AstraZeneca claimed its original efficacy numbers were based on an interim analysis of the trial data and an assessment of the final numbers have shown similar results. While the new numbers show that the widely used vaccine is robustly effective and offers complete protection against severe illness from Covid-19, the flip-flop could severely dent public confidence in the shot.

Big Number

30 million. That’s the total number of doses AstraZeneca expects to have ready in the U.S. at the beginning of April, which will allow it to quickly roll out large quantities of the vaccine if it is approved by the FDA.

Further Reading

AstraZeneca May Have Included ‘Outdated Information’ In U.S. Trial Results, NIAID Says (Forbes)

AstraZeneca Vaccine 100% Effective In Preventing Severe Disease And Hospitalizations, U.S. Trials Show (Forbes)

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