White Coat, Black Art·The Dose

'What if I've already had one dose?' Your AstraZeneca vaccine questions answered

Canadians have been on a roller-coaster with changing guidance on the AstraZeneca-Oxford vaccine, but an infectious disease specialist says there’s reason to be optimistic.

Infectious disease doctor urges Canadians not to despair over what may feel like a setback

Vials with the AstraZeneca-Oxford vaccine are pictured at the vaccination centre in Nuremberg, southern Germany, on March 18, 2021. Canada's advisory committee on vaccines recommended against the use of this COVID-19 vaccine for people under age 55. (Christof Stache/AFP/Getty Images)

Canadians have been on a roller-coaster with changing guidance on the AstraZeneca-Oxford vaccine, but an infectious disease specialist says there's reason to be optimistic.

Dr. Zain Chagla, an associate professor of medicine at McMaster University and physician at St. Joseph's Healthcare in Hamilton, Ont., said there's still time before those who've had one shot of AstraZeneca vaccine are due to have their second, and that studies being conducted right now will provide clear direction on how to proceed.

Guidance around who should have the AstraZeneca-Oxford vaccine has shifted a few times in recent months as more is learned about its efficacy and side effects.

On Monday, Canada's National Advisory Committee on Immunization updated its recommendations on the vaccine, advising against its use for people under 55 due to concerns about rare blood clotting incidents reported in Europe. (Health Canada said there have been no incidents of blood clotting from among the 300,000 doses of AstraZeneca vaccine administered here.) 

Dr. Zain Chagla is an infectious disease specialist in Hamilton, Ont., and an associate professor at McMaster University. He said there's still time to figure out the best course of action for Canadians who have received one dose of the AstraZeneca vaccine. (Craig Chivers/CBC)

Chagla urged Canadians not to despair over the latest of what may feel like a series of setbacks to Canada's vaccine effort. 

"Yes, there's a little bit of instability now with cases rising," he said. "But there is a hope out of all of this, and Israel and the United Kingdom are really showing us that these vaccines work well in a population. We just need time to get them out there."

Chagla joined Dr. Brian Goldman, host of The Dose and White Coat, Black Artto answer questions about AstraZeneca submitted by show listeners and to Ask CBC News at COVID@cbc.ca

Here is part of their conversation:

Why is the AztraZeneca-Oxford vaccine no longer indicated for people under 55?

So when this was being rolled out in the European Union, there was this signal toward a risk of blood clots, but particularly [in] young people with more than just the typical blood clots that you would see in the emergency room. They had very atypical blood clots, some of them in the brain, some of them in the abdominal vessels. And unfortunately, some of them actually passed away because of this.

So the initial data that was released from this issue of these atypical blood clots — a syndrome that we're now calling VIPIT, vaccine-induced prothrombotic immune thrombocytopenia — seem to be predominantly [seen in] women between the ages of 20 to 55, the absolute risk at about one in one million, although the German data suggests one in 100,000. When you start taking that into the context of the risk-benefit discussion around vaccines, especially in the context of us being fortunate in Canada to have other vaccines on the market, we start saying, well, the risk of death from COVID-19 in someone that's young is about two in 10,000. So you're starting to get into that same magnitude of risk of natural COVID-19 and complications as compared to the vaccine and its complications.

Again, this is the predominant group that seems to be at risk, so the numbers may actually be a bit smaller in that group, it may be closer to one in 10,000 because they're incorporating everyone into that one in 100,000 estimate, all old and young people. 

Why Canada's vaccine committee recommended a pause on AstraZeneca

1 year ago
Duration 7:03
'It has been very challenging as a committee to make recommendations on these vaccines and to be nimble and change recommendations when the data merits it,' says Dr. Shelley Deeks, vice-chair of the National Advisory Committee on Immunization.

Then you look at everyone else and say, actually, you're not seeing this [complication] in over 55-year-olds…. And add to that the risk of COVID-19 death is getting into the one per cent range or higher [in this group]; that risk-benefit argument favours so much more benefit [from the vaccine] in that population in over 55. This is where we got to where we're just balancing the risk.

There's still a lot to be determined about this vaccine. But for now, while we're getting data, we're going to take it away from the people that seem to be the highest risk of this complication and put it into people that are at the lowest risk of this complication, plus derive the most benefit from these vaccines. 

Any idea why it should be happening more in women under the age of 55?

It's unclear. There's a hypothesis that this is immune activation, whether or not this may deal with some of their underlying pro-thrombotic issues with hormones. Some of these women described in the first dataset had underlying autoimmune disorders, although some did not. The EU is going to be sitting down with virologists, infectious disease specialists, haematologists, pharmacologists, in the next couple of weeks to actually put together all of their data across all of their vaccine experience, including the U.K. And I think we'll get a better profile at that point of what these patients will look like, what risk factors they have, why they seem to be predisposed to it, and what we do to move forward.

Does being on the birth control pill increase risk? 

It might. Again, these numbers are still small. We're talking about 29 in 3 million [doses] in Germany. If we're talking about young women being at risk, part of that is going to be young women are typically on the birth control pill. Whether or not that's attributable risk is really, really hard to determine in these numbers. But we know birth control increases the risk of blood clotting, so, potentially this could be one of the factors involved.

When will those people who got the the AstraZeneca vaccine, who happen to be under the age of 55, know that they're in the clear? 

These reactions occurred between Day 4 and 20 after the vaccine. No cases were described after Day 20. And again, they seem to be relatively early after getting the vaccine. The things that people need to watch out for in that [period] are:

  • Bruising or bleeding easily
  • Chest pain
  • Leg swelling
  • Abdominal pain
  • A headache that is really unrelenting

If they are experiencing those symptoms, particularly Day 4 after the vaccine, that is an indication to seek medical help as there now are treatment protocols around this disorder and how to mitigate it with certain medications. 

If you're past Day 20, it seems like the risk is you're back to the baseline in terms of the general population. Again, we're talking one in a 100,000. That still means there's 99,999 people that got the vaccine that will not get this issue. And again, the odds are much in your favour that this is not going to happen.

What do we do with people under 55 that have gotten the first dose of AstraZeneca? 

The nice part of the AstraZeneca vaccine is that you don't need to give the second dose until week 12 or later, based on their own data. And so we have some time to let the dust settle. If we start figuring out there's a particular population, or there's a particular test we need to do in that population, to see whether or not they'll react, that's fine. And if we say that it's unsafe in that population in the three months, once the dust settles, then we theoretically could be offering other vaccines or waiting for a full series of another vaccine at that point.

We have clinical trials actually coming out now about other vaccines, so mixing MRNA and AstraZeneca vaccines together, and again, some of that data will actually come out in the next month or two.

Is there any evidence that getting the second shot of the AstraZeneca vaccine would increase your risk of this complication?

Right now, much of the data is around people that got their first dose … so we still don't know…. It's an evolving piece that we'll figure out. 

A 64-year-old receives a dose of AstraZeneca-Oxford's COVID-19 vaccine on Monday at Regina's mass drive-thru clinic. The rare blood clotting incidents that have emerged in Europe among AstraZeneca vaccine recipients have exclusively been in younger adults, mostly women between 20 and 55. (Saskatchewan Health Authority )

How do we balance that tiny risk against the risk of getting and dying of COVID during the third wave?

It's a really good point, and this is where we struggle. We obviously want a vaccine campaign that protects all of us, that protects the most vulnerable, but gives us the best chance of going back to normal and ending this public health emergency. But we have to recognize that these aren't just benign side effects. If this was a rash that, 14 days later, went away with a bit of Benadryl and everyone was fine afterwards, we'd accept that risk in the context of this.

There were people, unfortunately, with this reaction that succumbed to their illness. Right now we want to make sure that the vaccine campaign is safe, that the right vaccines are going to people, and all adverse events are mitigated for as many people as possible. We do not want people dying of a vaccine-induced side effect when it could have been prevented by giving another vaccine. So, yeah, I think this might slow down the rollout a little bit, but recognizing that we want to do this appropriately and safely.

For those over 55 who aren't sure they want their second dose of the AstraZeneca vaccine, is it fair to say there's no hurry?

Absolutely. Again, you get 70 per cent efficacy. The data from Scotland is a 94 percent reduction in hospitalizations past Day 28. You're deriving benefit from getting this vaccine working in your system now, and so there's not a rush to get another dose until we figure out what the appropriate strategy is moving forward. 

I really want to remind people we were talking about the pandemic starting a year ago, our lives being turned upside down. We're now talking about four vaccines, how to deploy them. Yes, there's a little bit of instability now with cases rising. But there is a hope out of all of this, and Israel and the United Kingdom are really showing us that these vaccines work well in a population. We just need time to get them out there.

Q&A edited for length and clarity. Written by Brandie Weikle. Produced by Willow Smith.


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