Some Canadian provinces treated mRNA vaccines as interchangeable. In Ontario a lot of people got a first dose of Pfizer and a second of Moderna.

There's currently a study underway in the UK (I forget the name, but it run by the University of Oxford) to assess the efficacy of mixed-dose vaccination.

More than mRNA vaccines as interchangeable, we (Ontario) mostly treated the oxford vaccine as interchangeable with the mRNA vaccines too, until we started giving it to less people.

Not gp, but I'm also a Canadian with the covid-cocktail. I got my Pfizer back in May, and then my Moderna at the beginning of July.

Some of the older (55+) crowd got a different mixture, with AstraZeneca shots in the early spring and Pfizer early summer.

Say what you will about our weird combos, but we have a very high number of people immunized now, so it seems to be working...

Same here in Canada. I got Pfizer through public health followed by Moderna 8 weeks later at a walk in pharmacy.

I’m Canadian and had one shot of AZ as a first dose. Followed by one shot of Moderna maybe 10 or 11 weeks after the first does of AZ.

Many Canadian provinces did a Moderna/Pfizer combo (one shot of each) to address shortages and get more people fully vaccinated faster.

It sounds like they were really following the science, and trying some new stuff along the way.

Yes, you should have seen how much complaining it generated!

The best combo so far (June) was AstraZeneca first then Pfizer (not the opposite, nothing then about Moderna), the next good one will be probably intranasal AstraZeneca after some mRNA:

Mixed Oxford/Pfizer vaccine schedules generate robust immune response against COVID-19, finds Oxford-led study: https://www.ox.ac.uk/news/2021-06-28-mixed-oxfordpfizer-vacc... ,

.. https://science.sciencemag.org/content/373/6553/397 - "the ideal vaccination strategy may use an intramuscular vaccine to elicit a long-lived systemic IgG response and a broad repertoire of central memory B and T cells, followed by an intranasal booster that recruits memory B and T cells to the nasal passages and further guides their differentiation toward mucosal protection, including IgA secretion and tissue-resident memory cells in the respiratory tract." .. (https://news.ycombinator.com/item?id=28019151),

https://news.ycombinator.com/item?id=28016821 - Covid-19 Vaccine Intranasal Study (COV008), UK phase 1 trial recruiting,

That said, current vaccines don't provoke the exact same response as an actual infection, particularly in that they don't fully stimulate an immune response in the mucous membranes of the upper repository tract. Here's an Scientific American round-up article (from back in March): https://www.scientificamerican.com/article/to-beat-covid-we-...

[..]

The current vaccines are excellent at helping the body stop the virus as it progresses into the lungs and further (thus the massive reduction in severe illness and deaths). But it still means that there's a period of a few days after initial infection when a vaccinated person has a relatively naive immune response (while the virus is mostly just in the nose/throat). This would then result in the person still being pretty contagious. (https://news.ycombinator.com/item?id=28014448).

I would like to see intranasal Novavax (intranasal mRNA is more difficult ?), having good results, as an option to this mix..