On March 18, the United Kingdom medicines regulator said that there had been five cases of a rare brain blood clot among 11 million administered shots.
The previously delayed shipment of 600,000 Moderna vaccine doses will arrive on Friday, with deliveries beginning on Saturday, the government's vaccine distribution czar, Canadian Army Major General Dany Fortin said.
"We are taking this very seriously", Professor Kidd said on Friday afternoon.
"This raises the possibility that the vaccine could be a causal factor in these rare and unusual cases of CVST, though we don't know this yet, so more research is urgently needed", said Prof David Werring, from the UCL Institute of Neurology.
He said people should be particularly alert to severe and persistent headaches that occu between four and 20 days after the vaccination, which "are different to your usual pattern of headaches" and do not settle with paracetomol or other over-the-counter painkillers.
"According to the current scientific knowledge, there is no evidence that would support restricting the use of this vaccine in any population", Cooke told reporters Wednesday. "One died and one also had a brain haemorrhage", it said.
The AstraZeneca and Pfizer vaccines have shown very high levels of protection against Covid-19, the agency said, adding that all vaccines and medicines have some side effects.
The Pfizer vaccine has been used predominantly to vaccinate frontline healthcare and quarantine workers.
This view is echoed by the World Health Organisation (WHO), which has urged countries to continue using the jab.
Among those affected by Germany's decision to halt the AstraZeneca vaccine's use in people under 60 were tens of thousands of teachers, who had only recently been offered appointments for the shot.
Cooke said the agency's assessment was based on 62 cases worldwide of unusual blood clots, including 14 deaths, reported to the EMA by March 22.
Investigations are under way to determine if the AstraZeneca vaccine is causing the very rare blood clots.
An AstraZeneca COVID-19 vaccine is prepared at the local vaccination centre as the spread of the coronavirus disease (COVID-19) continues in Hagen, Germany, on March 19, 2021.
The Australian Technical Advisory Group said there would be no change to the clinical guidance on the use of the AstraZeneca vaccine as a result of the EMA's findings.
In a statement it said: "ATAGI considers the benefits of vaccination in protecting people in Australia from Covid-19 outweigh the rare potential risk of these rare blood clotting events, and supports the continued rollout of the AstraZeneca vaccine in Australia". In late March, CSL Ltd began domestic production of 50 million doses.