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The World Health Organization (WHO) on Monday granted an emergency authorization to AstraZeneca's coronavirus vaccine, The Associated Press reports.

In a statement, the WHO said it was clearing the AstraZeneca vaccines made by the Serum Institute of India and South Korea's AstraZeneca-SKBio.

The WHO's green light for the AstraZeneca vaccine is only the second one the UN health agency has issued after authorizing the Pfizer-BioNTech vaccine in December.

The announcement should trigger the delivery of hundreds of millions of doses to countries that have signed up for the UN-backed COVAX effort, which aims to deliver vaccines to the world's most vulnerable people.

The AstraZeneca vaccine has already been authorized in more than 50 countries, including Britain, India, Argentina and Mexico.

In recent weeks, there have been concerns about the vaccine's effectiveness to global mutations, in particular a variant detected in South Africa.

A small clinical trial recently suggested that the Oxford-AstraZeneca isn't effective in preventing mild to moderate illness from the South African variant. South Africa later suspended the rollout of the vaccine in the country.

However, the WHO last week recommended the Oxford-AstraZeneca coronavirus vaccine for people over the age of 65 "even if variants are present".

On Saturday, Britain's University of Oxford, which developed the vaccine together with AstraZeneca, said it will test the impact of the vaccine on children.

The trial will assess the "safety and immune responses" in children and young adults aged between 6 and 17 of the vaccine, the university said in a statement.