Covid-19 vaccine Photograph:( Reuters )
During early trials, some volunteers had initially received half-dose vaccine in error which Oxford said was due to change "in the manufacturing process".
After acknowledging a key mistake in its vaccine dosage, AstraZeneca said that "additional study" was to validate the efficacy of the vaccine.
The British drugmaker had earlier said that average efficacy of the vaccine was 70 per cent. AstraZeneca has developed the vaccine in collaboration with Oxford University with several countries announcing their intention to buy the vaccine.
Meanwhile, US pharma giant Pfizer said it had begun the process of getting its new COVID-19 vaccine approved in Brazil.
"This is an important step so that the vaccine can be available in Brazil," Pfizer said in a statement as the company representatives met Brazil's National Health Oversight Agency (ANVISA) to begin the process of presenting the results.
Brazil is the worst-hit nations with the virus after the United States with over 6.1 million cases and over 170,760 deaths.
Brazil's health ministry had earlier agreed to buy 100 million doses of vaccine developed by AstraZeneca and Oxford University.
Mexico and Argentina had also concluded an agreement with AstraZeneca to produce the vaccine with Latin America battling the pandemic on a large scale. Mexico has registered nearly 102,000 coronavirus deaths which is the fourth highest in the world.
AstraZeneca's two-dose vaccine had given complicated results with the drug working 70 per cent of the time. During early trials, some volunteers had initially received half-dose in error which Oxford said was due to change "in the manufacturing process".
Amid the race for the vaccine, World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus said that since "initial supply of COVID-19 vaccines will be limited, so health workers, older people and other at-risk populations will be prioritised".
"The urgency with which vaccines have been developed must be matched by the same urgency to distribute them fairly," the WHO chief said.