AstraZeneca Updates Vaccine Efficacy in Dispute With US Agency

Peter Russell

March 25, 2021

AstraZeneca released additional data that it said confirmed efficacy of its COVID-19 vaccine after agencies in the US questioned the completeness of data from its interim phase 3 results.

In a statement this morning, AstraZeneca said efficacy of its AZD1222 vaccine at preventing symptomatic COVID-19 was 76%, occurring 15 days or more after 2 doses given 4 weeks apart.

That number stated in the latest press release was three percentage points lower than the headline efficacy of 79% that the British-Swedish pharmaceutical giant highlighted in a statement on Monday.

The confidence interval for efficacy at preventing symptomatic COVID-19 was between 68% and 82%, "consistent with the pre-specified interim analysis", the company said.

"In addition, results were comparable across age groups, with vaccine efficacy of 85% in adults 65 years and older," according to the statement. The confidence interval was between 58% and 95%.

Efficacy against severe or critical disease and hospitalisation was 100%, the statement read.

Furthermore, the AstraZeneca/Oxford vaccine "was well tolerated, and no safety concerns related to the vaccine were identified".

Rift Between Company and US Regulator

The results have been presented to the independent Data and Safety Monitoring Board (DSMB), which late on Monday expressed concern that AstraZeneca "may have provided an incomplete view of the efficacy data".

Since then, AstraZeneca had added an additional 49 cases to the interim analysis beyond the original February 17 cut-off.

Sir Mene Pangalos, executive vice president of AstraZeneca's biopharmaceuticals R&D, said: "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.

"We look forward to filing our regulatory submission for emergency use authorisation in the US and preparing for the rollout of millions of doses across America."

AstraZeneca said it would submit the primary analysis for peer-reviewed publication "in the coming weeks".

Dispute 'Will Not Benefit Global Health'

Dr Peter English, the former chair of the British Medical Association's Public Health Medicine Committee, said the difference in efficacy between 79% and 76% was "tiny, and to be expected with the number of cases analysed".

He told the Science Media Centre that the dispute over efficacy "could harm confidence in this vaccine in particular and, more dangerous still, to vaccination in general".

Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, questioned why the DSMB had raised concerns in public, "given the details of the relatively minor differences" set out in the latest AstraZeneca statement.

"There may be hidden reasons for their actions, but so far it will have had serious damage to public confidence in this, and possibly all vaccines, globally and it is unclear what benefits to anyone the DSMB's announcement will have had," he told the Science Media Centre.

He described an apparent breakdown in relations between the DSMB and the company as "sad" because the vaccine was "so important for global health, and the disputes do not promote global health".

"It would be better if this dispute could be laid to rest and the US and other regulators left to make their objective assessments of complete data without the glare of publicity," Prof Evans added.

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