The two vaccines that are authorized so far in Canada, the Pfizer-BioNTech and Moderna vaccines, are both two-dose vaccines. The reason that they're two-dose vaccines is really based on all of the developmental tests that have gone into the development of those vaccines, from animal studies and through lab studies to the clinical trials. The concern with only using one dose is that potentially that immunity could wane after a period of time. That's why one of the terms and conditions on both of those vaccine manufacturers is to continue to monitor the people in the clinical trial for up to two years.
The research that was done both in British Columbia and in Quebec is very important; we absolutely need research in the real-world application of the vaccination program. It was reassuring on two points, one is that we didn't have clinical trial information for people in the older age groups who were in long-term care facilities, so were potentially more frail. The concern in those groups is that potentially you could see less efficacy. One reassuring thing that this data has shown is that we are seeing a good response in those groups.
The vaccine effectiveness of the one dose was calculated using something called “crude vaccine effectiveness”; it's not comparing people who got the vaccine and who didn't get the vaccine, it's really looking at time frames within the groups who got the vaccine. It is useful, but it is limited. Right now, it's good information. I think the authors themselves noted that before they would recommend that we only have one dose more research needs to be done, but it is reassuring that if there is a delay for that second dose, it likely does not have a significant effect. The companies would have to come in if they wanted to change their vaccine to a one-dose vaccine with evidence to Health Canada. We would review that, and if it was suitable, we would change the labels.