The province of Ontario in Canada will stop offering first doses of British pharmaceutical company AstraZeneca's (LON:AZN) COVID-19 vaccine because of evidence that the risk of rare blood clots is somewhat higher than previously estimated, Reuters news agency reported on Wednesday.

Ontario's Chief Medical Officer, David Williams, was quoted as saying: "This decision was made out of an abundance of caution due to an observed increase in the rare blood clotting known as vaccine-induced immune thrombotic thrombocytopenia."

Williams added: "We are reviewing the data to consider options for the use of AstraZeneca for second doses and more broadly moving forward."