Health committee  This is something that I feel passionate about. I think we all, as public health professionals, feel passionate about this. When you're dealing with an epidemic or a pandemic, when you're dealing with a public health crisis, you need to use all the levers you have in order to interrupt transmission and to save lives.

Health committee  This is a matter of the evolution of the science. It's really as simple as that. We're learning more about the effectiveness of vaccines. We're learning more about the efficacy of one dose or two doses. This is all quite expected in the context of watching the population in its response to vaccines and watching vaccines as they interact with our population.

Health committee  Herd immunity, as you mentioned, is a concept that we hear about a lot. Some areas of science will put percentages around it, saying we need to reach a certain level of immunization in the population to achieve herd immunity. Others will talk about it in terms of time frame. From a public health perspective, we in the field are cautious when it comes to pronouncing on a particular percentage of the population required to achieve herd immunity, which is essentially a place where the virus can no longer efficiently transmit because people are protected; either they have been protected through vaccine-induced immunity or through natural infection and they are now immune.

Health committee  I would say, Mr. Chair, that the emergence of variants of concern has certainly added an important dimension to all of the work that we're doing under our vaccination strategy as we look at the effect on transmission and as we look at the effect on severity of disease. It does not change the plans, of course, that we have for rollout of vaccines; that continues to happen, and that needs to happen as it has been set out, but as we look at the effectiveness of vaccines, for certain, variants of concern matter as we assess vaccine effectiveness.

Health committee  Yes. NACI uses epidemiologic data. They look very carefully at the impact on population groups with respect to both the transmission of viruses, in this case SARS-CoV-2, and the impact on illness, particularly severe illness, hospitalization and death. When they do their analysis of a population subgroup, they see that certain groups including racialized communities and seniors are disproportionately affected by COVID-19: more illness, more severe illness, more death.

Health committee  Mr. Chair, I think that I may have indicated earlier that what we would like to do is bring that data back to the committee and we would undertake to do that.

Health committee  I'd be happy to do that. As Dr. Quach indicated, the National Advisory Committee on Immunization is a long-standing committee that has been providing advice to the Government of Canada, to the Public Health Agency, on the optimal use of vaccines in the population over many years.

Health committee  That is always part of the work we do with provinces and territories. What we will do is that we will bring the analysis that we receive through NACI. We will bring the analysis that we do ourselves—

Health committee  That analysis will be completed as we get more data and as NACI receives more data next week from Public Health England and from other sources, so it's premature to—

Health committee  No. I'm saying it's premature to bring forward the data, because we are awaiting it from another jurisdiction.

Health committee  There are data from some trials. We're waiting for NACI to consider it and synthesize it as they do for us as part of their mandate.

Health committee  Was that a question on timing?

Health committee  Yes, and so that is a question for the regulatory authority at Health Canada.

Health committee  I don't know if Dr. Poliquin would like to comment on that, but as you said, these studies are going on in the U.K. and are looking at combinations of Pfizer and AstraZeneca as a two-dose interchangeable approach to vaccination. From that perspective, we are awaiting the results of the U.K. study.

Health committee  If I may, Mr. Chair, there has not been a one-dose decision in the sense that NACI has provided its advice on the dose schedule for Pfizer and Moderna, and its current advice says that the dose interval should be no more than 42 days. As Dr. Quach said, NACI is now receiving evidence and research findings from Quebec, from the U.K. and other countries—