Thank you for the question.
I have read the data from the INSPQ, and it is very intriguing indeed. It's also very good to have 85% effectiveness in a very elderly and very sick population living in long-term care centres, or CHSLDs.
According to the immunological data, the second dose makes the antibodies become more mature and therefore much stronger and more active. It is as if a key fits even better in a lock, allowing for longer-term protection.
Using a single dose is risky right now since we don't have any data on a single-dose program. We may eventually get some.
For example, we have some data on the single-dose program with the Johnson & Johnson vaccine, but, given the little we know about it, that vaccine is slightly less effective against the South African variant. So the manufacturer is now conducting studies on adding a second dose to see if it will make any difference.
It's not so much the added 10% effectiveness that prompts us to give a second dose. It's really about longer-term protection. We wouldn't want to have to go through the vaccination process over and over again. We want people to be protected against the viruses that are circulating.
In addition, the study published by the INSPQ was conducted in Quebec at a time when we had no variants of concern. Effectiveness of 85% was only established for the field virus. We will need to continue to monitor. As Dr. De Serres said, when we see the effectiveness starting to drop, it will probably be time to give the second dose. For now, Quebec is planning a three-month interval between the two doses. So the initial deliveries will mean many more people can get vaccinated.