The British government formally asked the country's medicine regulator on Friday to assess Oxford University and AstraZeneca's COVID-19 vaccine.

UK Health Secretary Matt Hancock said he asked the Medicines and Healthcare Products Regulatory Agency (MHRA) to determine if the vaccine "meets rigorous safety standards."

AstraZeneca expects 4 million doses of its vaccine to be available in the country by the end of next month. The British government ordered 100 million doses of the vaccine and plans to begin distribution in December should it be approved.

Read more: Coronavirus: How Germany is preparing for a vaccination drive

The regulator said it could not give a time frame for its potential approval or rejection.

MHRA Chief Executive June Raine said, "no vaccine would be authorized for supply in the UK unless the expected standards of safety, quality and efficacy are met."

Serious concerns about testing

The results from the latest vaccine study were initially promising. Oxford and AstraZeneca said Monday that their vaccine could be up to 90% effective when given as a half dose followed by a full dose.

However, the drug makers later said a manufacturing issue resulted in "a half dose of the vaccine being administered as the first dose" to some participants.

Some scientists have expressed concerns about the gaps in the physical data and the way it was reported. Only 2,741 people received the half dose, while 8,895 study participants received two full doses.

Eleanor Riley, a professor of Immunology and Infectious Disease at the University of Edinburgh, said Oxford and Astrazeneca need to answer questions about the vaccine's efficacy "clearly and completely."

"Trust is at a premium when it comes to vaccines and we must not do anything that might in any way undermine that trust," said Riley.

Full results are expected in the medical journal The Lancet, but no date has been given. The MHRA approved the use of the half-dose/full-dose regime and allowed two groups to be tested seperately.

Despite the controversy, the UK's top science adviser said Thursday that the interim results showed the vaccine worked.

Read more: When will we have a COVID-19 vaccine?

"The headline result is the vaccine works and that's very exciting," said Patrick Vallance during a news conference with Prime Minister Boris Johnson.

It is the second vaccine to reach the formal assessment stage in the UK, after the shot developed by Pfizer and BioNTech made it to that point. A third vaccine from US firm Moderna should follow soon. All three vaccines showed high promise after initial testing.

kbd/sri (AP, Reuters)