The European Medicines Agency (EMA) on Thursday concluded that the AstraZeneca COVID-19 vaccine is "safe and effective," while not definitively ruling out possible links to rare blood clots accompanied by low levels of blood platelets.

Several European countries, including Germany, Portugal, Italy, Spain and Bulgaria, are set to resume use of the AstraZeneca vaccine next week following the EMA announcement.

British Prime Minister Boris Johnson said on Thursday that the Oxford/AstraZeneca and Pfizer COVID-19 vaccines being rolled out in Britain are safe and he was due to have an AstraZeneca jab on Friday.