Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization (WHO), said that the UN health agency "systematically reviews safety signals, and is carefully assessing the current reports on the AstraZeneca vaccine".

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The COVID-19 vaccine developed by AstraZeneca and the University of Oxford has been suspended in a number of countries across Europe and Asia, following reports of blood clots in some vaccinated people, reports Xinhua news agency. "WHO is aware that some countries have suspended the use of AstraZeneca vaccines, based on reports of blood clots in some people who received doses of the vaccine from two batches. This measure was taken as a precaution while a full investigation is finalized," Tedros said at a press briefing on March 12.

A number of countries like Denmark, Norway, Iceland, Romania and Thailand have suspended the rollout of the AstraZeneca/Oxford vaccine after it was linked to blood clots in recipients, while Austria and France have decided to continue using it. "It is important to note that the European Medicines Agency has said there is no indication of a link between the vaccine and blood clots, and that the vaccine can continue to be used while its investigation is ongoing," the WHO chief said.

The European Commission said on March 22 that the AstraZeneca vaccine is still safe to use, adding that the European Medicines Agency (EMA) had adopted a preliminary review on the case in Austria "where they said there is no specific indication that the vaccination led to these conditions". "As soon as WHO has gained a full understanding of these events, the findings and any changes to our current recommendations will be communicated immediately to the public," Tedros said.

The WHO chief also said that more than 335 million COVID-19 vaccine doses have been administered globally so far, and no deaths have been found to have been caused by them. "But at least 2.6 million people have been killed by the virus. And more will continue to die the longer it takes to distribute vaccines as rapidly and as equitably as possible," he said.

As countries roll out COVID-19 vaccines, the WHO is continuing to keep a close eye on their safety, Tedros added. Also on March 12, the WHO gave emergency use listing to Johnson & Johnson's COVID-19 vaccine, making it the fourth to receive the health agency's approval.

Emergency use listing is the green light for a vaccine to be procured and rolled out by COVAX, he said, referencing the global WHO-led initiative to ensure vaccine equity. As the world is struggling to contain the pandemic, vaccination is underway in an increasing number of countries with already-authorised coronavirus vaccines. Meanwhile, 263 candidate vaccines are still being developed worldwide, 81 of them in clinical trials, according to the WHO.