OTTAWA, Nov 18 (Reuters) - Canada will announce as expected on Friday it is authorizing the use of Pfizer Inc"s (PFE.N) COVID-19 vaccine for children aged 5 to 11, a government source said on Thursday. The decision will make it the first shot for young children in Canada. Officials had made clear for weeks that the decision would be favorable, noting that incidences of COVID-19 are now highest in those under 12. Prime Minister Justin Trudeau said last month that Ottawa had signed a deal with Pfizer to quickly receive 2.9 million doses of the vaccine once it was approved. read more The U.S. Food and Drug Administration authorized use of the vaccine for those aged 5 to 11 on Oct. 29. read more Rival firm Moderna Inc (MRNA.O) filed its own Canadian application for a children"s vaccine on Wednesday. The Canadian Pfizer announcement will be made at 10 a.m. (1500 GMT), said the source, who requested anonymity because of the sensitivity of the situation. The news was first reported by the Toronto Star newspaper.