The British-Swedish pharmaceutical manufacturer AstraZeneca on Wednesday revised down the effectiveness of its Covid vaccine by three percentage points after US authorities raised concerns that the results reported from the US trial were outdated.
The company now says its vaccine is 76 rather than 79 percent effective in preventing some form of symptomatic Covid.
It is still 100 percent effective against severe Covid, it added.
The move came after an independent panel of experts appointed to oversee the trial expressed concern that AstraZeneca had not included updated data in its originally published figure.
The US National Institutes of Health then issued a very unusual statement in which AstraZeneca would work with the panel and issue a new press release.
“We look forward to submitting our U.S. Emergency Use Authorization Report and preparing for the rollout of millions of doses across the United States,” said Mene Pangalo, Vice President of Biopharmaceutical Research and Development.
The new figure is based on 190 people who became ill among 32,449 trial participants in the United States, Peru and Chile, two-thirds of whom received the vaccine while the rest received placebo.
The previous figure was based on 141 cases, with a break in mid-February.
The company added that there are another 14 or probable Covid cases left to be assessed.
Depending on whether these occurred in the vaccine or placebo group, the final efficacy figure could go up or down a few percentage points.
The company added that the vaccine efficacy of people 65 years and older was 85 percent, but the statistical range for this figure – anywhere between 58 and 95 percent – makes it less meaningful and the sample size was not mentioned.
Eight cases of severe Covid occurred – all in the placebo group.
AstraZeneca was an early pioneer in the global race to develop a Covid vaccine and was strongly favored by the United States, which ordered 300 million doses – more than its first orders for Modern and Pfizer’s shots.
But a series of communication failures eroded the confidence of US agencies.
The United States now has three approved vaccines – Modern, Pfizer and Johnson & Johnson – and should have enough access to more than cover the adult population by the end of May.
However, approval from the Food and Drug Administration – which is considered the gold standard regulator – would go a long way to allay global doubts about the AstraZeneca vaccine.
Several European countries paused the launch of the shot at potential blood clot risks before later resuming use.
The European Medicines Agency considered the vaccine safe and said it was not associated with blood clotting in general – but added that it could not rule out a link to two very rare forms of coagulation, and suggested that these risks be mentioned on a warning label.
The AstraZeneca vaccine is still considered important for vaccinating the world due to its low cost and the fact that it can be stored for a long time at cold temperatures.
It uses an adenovirus that causes colds in chimpanzees, modified so that it cannot replicate, to carry the gene for a key protein in coronavirus in human cells.
The cells then produce the protein on their surface and train the immune system if it encounters the real virus.