OTTAWA -- With more doses of COVID-19 vaccine arriving in Canada and guidance changing on administering the shots to citizens, a microbiologist suggests the pandemic will "probably" be over in this country by September.

"I think we're about to go into that third act and finally put an end to the pandemic," said Jason Tetro, the author known as the Germ Guy, noting many people have been trained to be pessimistic this winter.

The first shipment of the Oxford-AstraZeneca COVID-19 vaccine arrived in Canada on Wednesday, the third COVID-19 vaccine approved for use in this country.

Late Wednesday, Canada's National Advisory Committee on Immunization issued new guidance on administering the COVID-19 vaccine. The panel of medical experts says the second dose of COVID-19 vaccines can be given up to four months after the first.

Tetro tells CTV News Ottawa that after a glum few months, there is reason for optimism.

"We've got lots of doses coming; we’ve got three approved, we've got two others that are in the pipeline. I think we're going to be definitely getting to that point where by the summer we're going to be in a very good position and probably see the end of this pandemic by September," said Tetro.

Prime Minister Justin Trudeau has said the government will have enough doses of the COVID-19 vaccine to vaccinate all Canadians by September. Trudeau said Wednesday he's "optimistic" the timeline could speed up.

"If we get to a point where we have the entire population vaccinated, at least with the first shot, it's probably going to get us to a point where we're going to be able to gather again, we may not even need the masks and while we still will probably be hesitant to get back to normal, we're going to start looking a lot better by that time," said Tetro.

The microbiologist says the arrival of the AstraZeneca vaccine gives Canada a variety of vaccine options to begin targeting different age groups.

Tetro adds the longer intervals between doses can speed up the timeline to vaccinate all Canadians against COVID-19.

"What we're trying to do now is to remove the pandemic status of COVID-19 and maybe even bring it down by the end of this year to what would essentially be a common cold and flu status," said Tetro.

He notes research from Scotland, Cambridge University in the United Kingdom and Israel shows one dose for all Canadians will make a difference.

"If we get everybody vaccinated with one dose, it doesn't matter which one it happens to be, that's going to give us the protection we need to be able to get through the seasonality and also to remove the pandemic emergency that we're currently living through now," said Tetro.