OTTAWA -- Canada is set to receive a large infusion of COVID-19 vaccines this week, even as questions swirl around how the immunization drive will be affected by the sudden departure of the man tasked with overseeing it.

The federal government says it expects around 4.5 million doses to arrive this week thanks to planned deliveries from Pfizer-BioNTech and Moderna.

Pfizer and BioNTech had been scheduled to deliver around 2 million doses this week as their vaccines continue to flow into Canada on a regular basis after early hiccups in February and March.

But the federal government says the two companies will ship an additional 1.4 million shots, which were originally slated to land next week but are now expected to arrive before the upcoming holiday weekend.

Moderna is also expected to deliver 1.1 million doses this week.

The large influx comes as the Liberal government faces questions about who will now lead the vaccination campaign after Maj.-Gen. Dany Fortin was sidelined suddenly on Friday and reassigned from his role presiding over the national inoculation effort.

The Department of National Defence has said Fortin is under military investigation, but otherwise refused to provide any details. The government, meanwhile, has yet to name a replacement.

There are also ongoing questions about the government's plans for the Oxford-AstraZeneca or Johnson and Johnson vaccines.

More than 655,000 shots of AstraZeneca arrived through the global vaccine-sharing initiative known as COVAX on Thursday, but most provinces have temporarily paused their use for first doses amid supply issues and the potential risk of rare blood clots.

As a result, the federal government has yet to distribute those shots to the provinces, though Ottawa says it expects to still receive another 1 million doses by the end of June.

About 2.16 million Canadians had received one dose of AstraZeneca as of May 8, and those additional doses could be used to give those people a second jab.

Health Canada also continues to review the quality of 300,000 Johnson and Johnson shots that were delivered last month, but have yet to be distributed.

The doses have been held back over concerns of possible tainting at a Baltimore production facility.

Health Canada chief medical adviser Dr. Supriya Sharma told CTV on Sunday that it could be weeks before the review is complete.

This report by The Canadian Press was first published May 17, 2021.