Health Committee on May 3rd, 2021

[Michelle Rempel, Conservative, Calgary Nose Hill, AB]

I'd love to get more information, but I only have a couple of minutes left. My apologies for cutting you off. I wish I had more time.

I'm wondering if, within your group or with any people you're working with in the government, you are looking at economic impact, mental health, other issues that may be arising as part of the restrictions, etc., and sort of marrying those together to come up with public health advice that looks at all aspects of what the country is going through right now.

[Dr. Timothy Evans]

The closest we would come to informing discussions on that is our work on modelling trajectories toward herd immunity, because that's really going to be the evidence that allows us to understand just how long we're going to be in this crisis.

[Michelle Rempel, Conservative, Calgary Nose Hill, AB]

Do you have any data on the causality of inequalities in COVID-19 immunity, which you mentioned, that you could table with the committee?

[Dr. Timothy Evans]

I have data on the seroprevalence surveys. We do not have data on the causality at the moment, no.

[Michelle Rempel, Conservative, Calgary Nose Hill, AB]

Is anybody working on causality?

[Dr. Timothy Evans]

I think many investigators will be looking at this, and I've seen various studies, but I don't have a definitive list for you at this time.

[Michelle Rempel, Conservative, Calgary Nose Hill, AB]

As well, with regard to the dosing interval, are there any studies in Canada right now on waning or potential waning immunity at different data points over a four-month dosing interval for all the vaccines that have been approved for use in Canada?

[Dr. Timothy Evans]

There are a number of provinces that have provincial surveillance systems. In particular, British Columbia and Quebec have very good surveillance systems looking at the trends in immunity over time with a single dose, or the “first dose fast” strategy.

The task force has supported studies that are looking at measures of immune function over time and how they differ. I mentioned one of the studies in my remarks related to long-term care residents.

[Michelle Rempel, Conservative, Calgary Nose Hill, AB]

In closing, my understanding is that there isn't any data that you or anybody could point this committee to on immunity levels after one dose at a four-month interval for, let's say, the Pfizer vaccine. If there is, I'd love to know what that is.

[Dr. Timothy Evans]

The country that's furthest ahead in this is the U.K. They published data last week that gives us an indication of the effectiveness of a single dose in that population as much as 12 weeks out. I don't think they have the 16-week data at this time, so we'll have to wait a little longer for that.

[The Chair, Liberal, Ron McKinnon]

Thank you, Ms. Rempel Garner.

We'll go now to Ms. O'Connell.

Ms. O'Connell, please go ahead, for six minutes.

[Jennifer O'Connell, Liberal, Pickering—Uxbridge, ON]

Thank you, Chair.

Dr. Evans, my questions are for you as well.

I'm picking up on that international piece that you were just speaking of. Obviously there's lots of data, but some of the helpful data that I think a lot of us are looking to is from the U.K. and Israel.

You mentioned that the only way to get to herd immunity is through vaccination. One of the things we've noticed is this idea of loosening public health measures too soon, and Israel and the U.K. had instances of this.

I'm curious whether you're looking at this. How much do you factor in that international kind of experience in your work? I would assume, given the topic, that any data is helpful, but in terms of spikes until vaccinations can do their work, do you have any models or indicators that would be helpful in determining some of that balance between public health measures and vaccinations, moving out?

[Dr. Timothy Evans]

I have a couple of quick things to say.

The first is that, yes, the international experience is extremely important and in part because the U.K. and Israel, as you mentioned, were well ahead of Canada in the rollout of their vaccines. They have a time advantage on us. In addition—and I'd like to mention this very clearly—there are much more unified data systems across their countries. This is a barrier in Canada that we need to address. The fact that they have this data now, with vaccine coverage rates that are over 50%, is very helpful in understanding and informing our models related to herd immunity.

The U.K. is particularly relevant because they have adopted this “first dose fast” strategy. What we can see from the data at the moment is that this strategy has been very successful in curbing the third wave. That, to me, suggests that the approach Canada has adopted, similar to the U.K.'s, holds promise for getting us through this third wave and stresses the importance of accelerating the vaccine rollout as fast as possible.

[Jennifer O'Connell, Liberal, Pickering—Uxbridge, ON]

To follow up on this international theme, obviously everybody wants to be done with COVID and wants to understand what they can start to do if they're fully vaccinated. We are starting to see bits and pieces of this in different countries around the world. I know it's something you're looking at too, in the immunity data. However, the challenge I have is that sometimes this can be a bit unhelpful in the sense that if we don't have a recognized sense of immunity understanding, some jurisdictions can say you can do x or y, and can then pull that back.

Do you see that as a challenge, this constant struggle? Everybody obviously wants to travel or do things again. Where do you see us, in understanding the immunity data, with vaccines, taking into account the variants? Maybe that's an unfair question, but it's about a balance between moving ahead and having some kind of unified understanding of what immunity means when you're fully vaccinated.

[Dr. Timothy Evans]

That's an excellent question, and there are three dimensions of it that I'd like to address.

First, I think we're much closer today to having immune measures that are what we call correlates of protection. Not to go into detail, but anybody who has gone into the depths of immunology will know that there's nothing simple here: It's a very complex immune system we all have. Therefore, generalizing with unified measures across immune systems has taken a lot of work. However, there's been tremendous progress over the last year, and I believe we're much closer to having accepted measures of correlates of protection. These are biological measures of immunity that will allow us to understand how protected we are after vaccines or natural infection. That's inclusive of variants.

The second part of this is the variants of concern that have recently emerged. We're actively working with the variants network that Canada has set up to understand the interfaces between vaccines and immunity. We're getting data on that, and at the moment the initial evidence suggests that the vaccines are perhaps more robust than we would have expected in the context of the variants.

The last point is about public health vigilance and behaviours. I think we may see an opportunity to dial those back when we get 50% to 60% of Canadians vaccinated. However, before that time, we really have to continue to promote adherence to public health measures, which we know make a difference.

[Jennifer O'Connell, Liberal, Pickering—Uxbridge, ON]

Thank you very much.

I'm sorry to the other witnesses. I didn't have time to get to you, but hopefully my colleagues will.

Thank you, Chair.

[The Chair, Liberal, Ron McKinnon]

Thank you, Ms. O'Connell.

Mr. Thériault, you now have six minutes.

[Luc Thériault, Bloc, Montcalm, QC]

Thank you, Mr. Chair.

I'll begin with Dr. Evans, and I would like to come back to the previous questions.

Dr. Evans, you just said that it might be possible to relax the health measures once 50% to 60% of people are vaccinated. Are you talking about a first dose or full vaccination?

Also, you were saying earlier that we aren't close to herd immunity. I'd like to know roughly when we will be. If we're not close to herd immunity and the health measures are relaxed, aren't we running the risk of going back to square one?

You also mentioned that immunity following infection lasts for eight months. Could you tell me how that was determined? Are we talking about full immunity? What about immunity from the first dose?

I'll stop there for now and let you answer my questions.

[Dr. Timothy Evans]

Thank you for these questions.

I'll begin by saying that the vaccination rate of 50% to 60% is a minimum. In the UK, 50% to 53% of the population has received a first dose of the vaccine, and we're seeing that the infection rate continues to drop there.

I believe that a similar situation could exist in Canada. The big difference is that our immunity rate is much lower because fewer people have been infected with the virus. So it's possible that we'll need to reach a 60% or 65% vaccination rate before health measures are relaxed, but we'll see.

As for herd immunity, I think we'll have to continue following all public health measures until there's a significant drop in the infection rate. We can all agree that we haven't yet reached that point, so it's absolutely necessary to continue to follow all public health measures.

[Luc Thériault, Bloc, Montcalm, QC]

You say that we could start to relax health measures a bit once 55% to 60% of the population has received a first dose.

Does that mean that you agree with the strategy of giving a first dose of the vaccine to as many people as possible, regardless of the time frame for the second dose?

That's what's happening now, and you're saying that we could start to relax health measures.

[Dr. Timothy Evans]

All the data I've seen to date support this strategy. I think there are certain groups in the population that need to be considered, especially the elderly and those with immune deficiencies. They may need to have a second dose sooner, or as soon as possible.

Regarding the other question about the immunity obtained after infection, this is a natural infection. There was a study done at the University of Montreal by Professor Andrés Finzi, who followed up on a population of patients who had been infected. I think they have more details now, but a few weeks ago it was concluded with certainty that for the first eight months there was strong immunity related to long-term immunological memory. That doesn't mean it's complete immunity, but it's very strong.

The study hasn't yet determined the rate of infection among these people, but from the immune tests, we have important data showing that the immune system is still very effective against new infections.

[Luc Thériault, Bloc, Montcalm, QC]

Is this always the case, regardless of the initial viral load? These are people who are still alive and who haven't had serious enough after-effects to prevent them from participating in a study. Is that right?

[Dr. Timothy Evans]

I believe that most of the people who took part in the study had been hospitalized following infection.

[Luc Thériault, Bloc, Montcalm, QC]

Thank you.

[The Chair, Liberal, Ron McKinnon]

Thank you, Mr. Thériault.

We will now go to Mr. Davies.

You have six minutes, Mr. Davies.