Health Canada is demanding that AstraZeneca do a detailed study on the risks and benefits of its COVID-19 vaccine across multiple age groups.
That's after getting more reports that patients in Europe developed blood clots following vaccination.
The agency says it has not received any reports of blood clots in Canada to date.
The regulators that review and authorize vaccines are not pulling AstraZeneca's approval in Canada but say regulatory changes could still be made depending on what the results of this study show.
A statement from Health Canada reads ``Health Canada's guidance issued to health-care practitioners last week still stands, and provides vaccine recipients with information on the signs and symptoms to monitor for following vaccination.
Last week, the department changed its label on the vaccine to warn about the rare risk of blood clots.
The National Advisory Committee on Immunizations this afternoon recommended against the vaccine's use for anyone under the age of 55.
NACI provides advice to the provinces on how approved vaccines should be used in the context of the entire number of vaccines available.
Provincial governments decide on their own how to use a vaccine, but several have announced plans to stop using it on people under 55, including Prince Edward Island and Quebec.