Europe reviews clot reports post-AstraZeneca vaccination. Here's what you need to know

More than 45 million COVID shots by all manufacturers have been administered across the EU and the European Economic Area since vaccinations started almost three months ago. The EMA is investigating reports of 30 cases of unusual blood disorders out of 5 million people who got the AstraZeneca vaccine in the EU. The EMA's focus and primary concern is on cases of blood clots in the head, a rare condition that's difficult to treat called cerebral venous thrombosis (CVT).

In Germany, seven people aged 20 to 50 have been diagnosed with CVT up to 16 days after vaccination as per Monday, according to the national vaccine authority Paul Ehrlich Institute (PEI). Based on the known rate of CVT in the general population, the PEI would have expected one case in 1.6 million. Britain has administered more than 11 million doses of the AstraZeneca vaccine and reports of blood clots were no greater than would have occurred naturally. The UK's medicine regulator has urged Britons to keep on getting their vaccines, including the AstraZeneca shot.

Canada has said health experts are sure all COVID-19 vaccines being administered in the country are safe, including AstraZeneca's. AstraZeneca said on Sunday a review of safety data of more than 17 million people vaccinated in the United Kingdom and European Union with its vaccine had shown no evidence of an increased risk of blood clots. EMA investigators are checking if the frequency of incidences is higher in the vaccinated population than normal background rates.

The normal frequency is drawn from public health statistics or insurance records. This would be combined with a medical analysis of each case and insight from scientific literature. EMA's head of safety monitoring, Peter Arlett, added the rarity of CVT meant the watchdog would have to rely more heavily on case-by-case analysis rather than on the sparse statistical data. A spokeswoman for Germany's vaccine authority, which is part of the investigation, said EMA would not rule on causality. Instead, EMA will assess the likelihood of an increased risk of the condition and weigh that against the benefits of fighting COVID-19 and providing relief for health systems.