AstraZeneca COVID-19 Vaccine Updated Trial Results Cut Efficacy Rate

AstraZeneca has released updated data on its COVID-19 vaccine efficacy, after being criticized earlier this week for using outdated information for its initial report. On Monday, the pharma company announced its AZD1222 vaccine candidate saw 79-percent efficacy at preventing symptomatic coronavirus in a US trial; today, it trimmed that figure to 76-percent efficacy.

"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, Executive Vice President, BioPharmaceuticals R&D, said of the updated results. "We look forward to filing our regulatory submission for Emergency Use Authorization in the US and preparing for the rollout of millions of doses across America."

The vaccine candidate remains 100-percent effective against severe or critical cases of COVID-19, the study suggests, and against hospitalization. In participants aged 65 years or older, it's 85-percent effective against symptomatic COVID-19. A total of 32,449 participants took part in the trial and had their results included in this updated primary efficacy analysis, with 190 symptomatic cases recorded in total.

Of those cases, only eight were classified as "severe" infections with COVID-19. All of those patients were in the placebo group, not the cohort of people given the AstraZeneca vaccine candidate.

It's been a tricky few weeks for the pharma company, and its partners at the University of Oxford in the UK which helped develop the AZD1222 vaccine candidate in the first place. Early positive results in trials led to it being the first of the COVID-19 immunizations to be deployed, but several countries subsequently halted its use after reports of blood clots in some who had been vaccinated. The European Medicines Agency has denied any extra risk of that from AZD1222, however.

Still, that controversy was hanging over AstraZeneca's corporate head when its results were examined by the Data and Safety Monitoring Board (DSMB) and the National Institute of Allergy and Infectious Diseases (NIAID) in the US earlier this week. "The DSMB expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data," the NIAID said on Tuesday. "We urge the company to work with the DSMB to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible."

That's what has happened today. AstraZeneca maintains that its updated results are "consistent with the pre-specified interim analysis" from earlier this week. It also added in results of 49 more cases of COVID-19, and said that "14 additional possible or probable cases" remain which could also slightly change the final figures. AstraZeneca plans to submit its primary analysis for publication in a peer-reviewed journal "in the coming weeks."

Like the Moderna and Pfizer COVID-19 vaccines, AstraZeneca's requires two shots for maximum effectiveness. The company says that early data indicates an uptick in efficacy with a longer period – of up to twelve weeks – between those two immunizations.