Leaving aside a dramatic rebuke from government researchers and independent experts, AstraZeneca announced on Wednesday night that a new analysis concluded that its COVID-19 vaccine was 76% effective in preventing symptomatic COVID-19 – below the estimate of 79% effectiveness announced in a press release Monday.
The new estimate is still high, according to an independent board of experts charged with overseeing vaccine testing and data analysis. The study’s Data and Security Monitoring Board (DSMB) sent a highly unusual letter to AstraZeneca shortly after Monday’s press release, noting that the study data it had seen during the February and March meetings suggested that the vaccine effectiveness was actually between 69% and 74%.
“The DSMB is concerned that AstraZeneca has chosen to use data that was already out of date and potentially misleading in its press release,” says the letter. “What is clear to the council is that the [vaccine efficacy number]… they chose to release it was the most favorable for the study as opposed to the most recent and complete. Decisions like this are what erode public confidence in the scientific process. “
In an equally impressive statement issued early Tuesday, the National Institute of Allergy and Infectious Diseases echoed the point that AstraZeneca’s press release on Monday may have “provided an incomplete view of the efficacy data”.
“We urge the company to work with the DSMB to review effectiveness data and ensure that the most accurate and up-to-date effectiveness data is made public as soon as possible,” says the NIAID statement.
AstraZeneca is maintaining its previous effectiveness estimate, however. In Wednesday night’s announcement, the company said the most recent estimate is “consistent with the pre-specified interim analysis announced on Monday, March 22, 2021”.
New numbers
According to the company, the new review of the trial of 32,449 people included 190 symptomatic cases, up from the 141 symptomatic cases included in Monday’s analysis.
Based on these 190 cases, the vaccine appeared 76% effective in preventing symptomatic diseases that occurred 15 days or more after receiving the second of the two doses, administered four weeks apart. The confidence interval for the estimate – which suggests the plausible range of effectiveness based on the data – was between 68% and 82%, the company noted.
AstraZeneca added that, as before, the vaccine’s effectiveness seemed comparable across age groups, with an estimated effectiveness of 85 percent in people aged 65 and over. The vaccine appeared again to prevent serious illnesses. Eight cases of severe COVID-19 were included in the new analysis, all in people who received a placebo. None of the vaccinated participants required hospitalization and the company still did not see safety concerns with the vaccine.
“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 65 and older,” said Mene Pangalos, executive at AstraZeneca, in Wednesday’s announcement. “We are looking forward to submitting our regulatory application for Emergency Use Authorization in the U.S. and preparing for the launch of millions of doses across America.”
The announcement noted that the most recent results “have been presented to the independent Data Security Monitoring Council”.