A test tube labeled with the vaccine is seen in front of AstraZeneca logo in this illustration taken, September 9, 2020 Photograph:( Reuters )
A statement describing the error on Wednesday came days after the company and the university described the shots as "highly effective" and made no mention of why some study participants didn't receive as much vaccine in the first of two shots as expected.
Days after the company and the university described the Covid vaccine shots as "highly effective", AstraZeneca and Oxford University have acknowledged a manufacturing error that is raising questions about preliminary results of their experimental COVID-19 vaccine.
Also read: Oxford-AstraZeneca Covid-19 vaccine shows 70% efficacy; can be 90% effective, trial data reveals
On November 23, British-Swedish drug maker AstraZeneca and the University of Oxford had said that the Coronavirus vaccine they are developing is 70.4 per cent effective, on an average, in preventing COVID-19, as per the interim analysis of its late-stage clinical trials conducted in the UK and Brazil.
A statement describing the error made no mention of why some study participants didn't receive as much vaccine in the first of two shots as expected.
In a surprise, the group of volunteers that got a lower dose seemed to be much better protected than the volunteers who got two full doses.
In the low-dose group, AstraZeneca said, the vaccine appeared to be 90 per cent effective.
In the group that got two full doses, the vaccine appeared to be 62 per cent effective.
But the way in which the results were arrived at and reported by the companies has led to pointed questions from experts.
The partial results announced on Monday are from large ongoing studies in the UK and Brazil designed to determine the optimal dose of vaccine, as well as examine safety and effectiveness.
Multiple combinations and doses were tried in the volunteers.
They were compared to others who were given a meningitis vaccine or a saline shot.
Meanwhile, China's leading vaccine producer Sinopharm announced on Wednesday that it has submitted an application to the Chinese authorities for marketisation of its COVID-19 vaccine based on data collected from countries carrying out its clinical trials.
A representative of Sinopharm told state-run Global Times that the company had collected data from major countries such as UAE carrying out its vaccine clinical trials.
Results are expected to be good but it is up to the Chinese authorities to make the decision as the government has strict review standards.
Sinopharm previously told the daily that it had reported the phase-III clinical data to China's State Food and Drug Administration and was in the process of giving more detailed data, as requested.
The vaccine maker says it is in the final stage before marketisation, and is now making approval for the marketisation of the vaccine its top priority.
It will be possible to release the phase three data in academic journals after the approval.
"Our data is evaluated by relevant departments following protocols even stricter than in some Western countries, and we are in close communication with the WHO," a representative of Sinopharm told the daily earlier.
A Chinese Foreign Ministry spokesman Zhao Lijian told a media briefing last week that five Chinese vaccine candidates are under clinical trials in countries including the UAE, Brazil, Pakistan and Peru.
Sinopharm, China's state-owned vaccine producer, said on November 19 that its vaccine has been administered to about a million people under the government's emergency use scheme.
"In terms of emergency use, the vaccines were applied to nearly a million people and there has not been a single case of a serious adverse event. People have had only mild symptoms," Liu Jingzhen, chairman of China National Pharmaceutical Group (Sinopharm), said in an interview with a Sichuan-based digital media company that was published on Wednesday.
"Until now, all our progress, from research to clinical trials to production and emergency use, we have been leading the world," he was quoted as saying by the Hong Kong-based South China Morning Post on last Thursday.
His comments came amid criticism that Chinese firms have not publicised the clinical data of its vaccine studies.
(With inputs from agencies)