Pharmaceutical company AstraZeneca has released additional data that it said confirms the efficacy of its Covid-19 vaccine after questions about interim clinical trial results were raised in the US by an independent agency. But the additional data suggests the vaccine is slightly – but not significantly – less effective than the interim results suggested.
Interim results released by AstraZeneca on Monday from the phase-3 clinical trial of more than 32,000 people found the vaccine was 79% effective against symptomatic disease and 100% effective against severe disease and death. But soon after the results were published, the Data and Safety Monitoring Board in the US said it was concerned AstraZeneca may have provided “outdated information” from the trial, which gave “an incomplete view” of the results.
The US National Institute of Health (NIH) outlined the concerns raised by the board in a press release.
In response, AstraZeneca on Thursday released the additional data, which it said confirmed the efficacy results from the interim analysis. The data has been presented to the Data Safety Monitoring Board. An additional 49 cases were added to the previously announced results.
Astrazeneca said in a statement that when the new data was added, they found: “The primary endpoint, vaccine efficacy at preventing symptomatic Covid-19 was 76% occurring 15 days or more after receiving two doses given four weeks apart.”
This is slightly lower than the 79% efficacy originally reported.
“In addition, results were comparable across age groups, with vaccine efficacy of 85% in adults 65 years and older,” the statement said. “A key secondary endpoint, preventing severe or critical disease and hospitalisation, demonstrated 100% efficacy.”
The vaccine was well tolerated and no safety concerns related to the vaccine were identified, the findings show. While the result appears to show a slightly lower efficacy, the newer figure has a confidence interval of between 68% to 82%. This means there is a 95% chance that the true efficacy of the vaccine is between 68% to 82%, making it similar to other vaccines including Pfizer’s. As more data is added, the confidence interval usually tightens and provides more certainty.
A professor of epidemiology with La Trobe University in Australia, Hassan Vally, said the difference between 76% and 79% was not significant.
“In the scheme of things it’s not changing anything when you take into consideration the confidence intervals,” Vally said.
Mene Pangalos, the executive vice-president of AstraZeneca’s bio pharmaceuticals research and development, 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.”
AstraZeneca will also submit the analysis for peer-reviewed publication in the coming weeks.
Associate Prof Paul Griffin, the director of infectious diseases at Mater Health Services in Australia, said people could believe in the vaccine and that it was safe and effective.
“It is such a shame that a vaccine with so much evidence supporting its safety as well as efficacy continues to be shrouded in controversy,” he said.
“We heard very positive news almost a week ago that the European Medical Authority’s safety committee concluded that the vaccine was not associated with an increase in the overall risk of blood clots and therefore the benefits of receiving the vaccine continue to outweigh the risk of side effects.”
The request for more vaccine data was standard practice in drugs approval processes but played out very publicly due to the intense focus on Covid and the need for transparency, Griffin said, but it was important not to overreact when questions were raised.
“Unfortunately, after appearing to have all of the perceived issues addressed, the NIH statement yesterday has once again fuelled some scepticism with relation to this vaccine,” he said.
“This was based on some reported concern by the Data Safety Monitoring Board that outdated information may have been included, thus providing an incomplete view of the efficacy. To me, this seems like a highly atypical approach to resolving an issue such as this and is very unfortunate in terms of the perception of this vaccine.”