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So, you got AstraZeneca. Here’s what experts say about mixing doses, variants and more

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Those who received AstraZeneca as a first dose of COVID-19 vaccine have found themselves at a crossroads once again, now that the national advisory committee is recommending that other, mRNA vaccines be given as a second dose whenever possible.

Health experts stress — often, more than once — this doesn’t mean that AstraZeneca is a bad vaccine. They say the new advice reflects new information. A very rare risk of side effects combined with the large incoming shipments of mRNA vaccines means that a change of course might make sense.

But there’s no question the changing advice has been confusing.

Toronto resident Alex Colangelo got a first dose of AstraZeneca in April and booked a second mRNA dose for July. He recently called a pharmacy, however, and found he could get a second dose of AstraZeneca almost immediately, or an mRNA a few days later.

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While Colangelo, who takes immunosuppressing medication, opted to wait a couple of days for an mRNA dose, he says if Astra Zeneca had been the only option available for a few weeks it would have been a “tough call.”

“We are trying to make decisions that, I think, a lot of people don’t have the background to make with confidence,” he said. “We’re left to our own devices to figure out the science and the risks.”

With that in mind, we put your questions to the experts.

Should I panic?

No! While the communication here has been less than clear, Eleanor Fish, a professor of immunology at the University of Toronto, says “the notion that we’re switching away from AstraZeneca because it is a potentially harmful vaccine is just absolutely incorrect.”

These are all new vaccines, and while we learned a lot about them through the trials that were conducted on thousands of people before the vaccines were authorized, we’re continuing to learn even more as they’re used around the world. It makes sense to update guidance as we go, Fish says.

“This is exactly how what we call ‘post-marketing surveillance’ is meant to work,” she says.

So what new evidence does NACI have?

According to the new guidance posted this week, the decision to tell people to get an mRNA vaccine — meaning Pfizer or Moderna — for their second dose, was based on new information from Germany that suggests AstraZeneca followed by Pfizer resulted in a “potentially better immune response.”

Germany has had a similarly winding road with the AstraZeneca vaccine to Canada. When it was first approved in Europe, it was offered to all adults in country. But in April, when the dose started being linked to rare blood clots, particularly in young women, the Germany Standing Committee on Vaccination limited it those over the age of 60.

The result was a real-world experiment. All of a sudden, a whole bunch of younger adults in Germany had to get Pfizer or Moderna as their second shot.

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Researchers at Saarland University in western Germany were watching, and found that people who had received a shot of AstraZeneca and a shot of Pfizer had an immune response that was stronger than if they had been given two of either shot.

I’m hearing a lot about the Delta variant. What’s most effective against it?

Both AstraZeneca and the mRNA vaccines seem to be a little bit less effective against the Delta variant.

According to a study from Scotland published in the Lancet this week, the Pfizer vaccine was about 92 per cent effective against the Alpha variant, which originated in the U.K., in terms of infection, but only about 79 per cent against the Delta variant.

AstraZeneca was about 73 per cent effective against infection by the Alpha variant and 60 per cent against Delta.

What do you mean by ‘effective’?

This is an important part of the conversation.

Most efficacy data refers to how well the vaccines prevent infection. However, that’s only one way to evaluate how good a vaccine is.

There’s also the question of how well they prevent severe COVID-19 consequences — and they seem to be equally good at that.

An analysis of British data published this week suggests that AstraZeneca and mRNA vaccines are good at making sure, if you get COVID from the Delta variant, you won’t be sick enough to end up in the hospital.

According to Public Health England, the Pfizer vaccine is 96 per cent effective against hospitalization, while AstraZeneca is about 92 per cent effective.

That means they’re both about as good at avoiding severe COVID-19 with Delta as they are with Alpha.

What if I only have one shot?

Only having one shot of either also leaves you vulnerable. According to British data reported in the Guardian, one shot of Pfizer was about 36 per cent effective against symptomatic disease, whereas AstraZeneca is about 30 per cent.

Does it matter if it’s Pfizer or Moderna?

Not really. Both Pfizer and Moderna are based on the same mRNA technology.

That means they both work the same way, are very effective and have similar side-effects, says Dr. Lawrence Loh, the medical officer of health for the Peel Region.

“I mean, I received Moderna myself,” he continues, “and I was very happy to receive Moderna, because now I share a vaccine story with Dr. Tony Fauci and Dolly Parton, which I think is really great.

“But just to be clear, I would have been happy with either mRNA product or even with AstraZeneca at the height of the third wave, when it was when it was offered.”

What if I want AstraZeneca as a second shot?

While he wouldn’t necessarily recommend AstraZeneca over an mRNA to one of his patients, Dr. Peter Juni, the scientific director of the Ontario COVID-19 Science Table, said he has “no problem” if someone were to do the research and choose it for themselves.

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There might be people who have a brand familiarity with AstraZeneca, or live in an area where it’s easier to get, Loh adds.

“I think, overall, the recommendation is while they may prefer an mRNA as the second dose, they do still say that two doses of AZ will give you a very good protection.”

Does this mean we know for sure that mixing doses is better?

No. The German study was pretty small — about 250 people participating, according to Deutsche Welle — and the full results still need to be analyzed.

But it’s a positive sign that this strategy could work.

Fish adds that while it’s important to have data to confirm this, mixing vaccines is a pretty common strategy.

“My perspective as an immunologist, as a scientist, is that we know that it’s very often a good idea to mix and match different platforms,” she says.

“Because that will add an added advantage to your immune system.”

When will we know more?

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The major study that most of the world has been waiting on is large-scale trial at the University of Oxford, which, for months, has been studying the effects of various two-dose combinations of Pfizer, AstraZeneca, Moderna and Novavax vaccines.

While early results show the approach is safe, though possibly with an uptick in side-effects, the final data on how well it works hasn’t been released yet — but should be soon.

So if I’ve had a first dose of AstraZeneca, what should I do for my second?

To be clear, the national committee is recommending Pfizer or Moderna as a second shot.

But they’ve left the door open to choice.

“The easiest way for me to say it is, ‘You can get the same thing you got as your first dose or any of the mRNA vaccines,’” says Loh.

There are pros and cons to both options, says Dr. Lynora Saxinger, an infectious disease expert at the University of Alberta.

In short, the AstraZeneca vaccine is very effective but might be slightly less protective against infection by the new Delta variant. However, it would still most likely stop you from getting serious COVID-19 symptoms.

Getting a second mRNA shot is safe and might offer you better protection against Delta, but because we only have early data on this while we wait for the results of the big Oxford trial, that conclusion is still “speculative.”

“I think it depends on what you value when you’re weighing these different pieces of information,” she says.

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“If you’re a person who likes a higher degree of certainty, I don’t think it’s wrong to select the second dose of AstraZeneca,” she says.

“At the moment, if you lived in an area where there was a rapid expansion of Delta, I would tend to say I’d fall off the fence more in the direction of the mRNA vaccine.”

What if I’ve already had two shots of AstraZeneca?

You still have really good protection so try not to worry, Fish says.

It may not be as good against infection as someone who has gotten two mRNA shots, but you’ve got about the same defence against getting a severe case of COVID.

“I think team AstraZeneca has really been excellent, because they stepped up to the plate. They went with what was being suggested, and then they had to go through this period of uncertainty, which is kind of unfair,” Saxinger add.

“I don’t think anyone should regret getting AstraZeneca.

“It still provides good protection against severe disease, variants, and you might end up getting another booster at some point anyway.”

What’s this about boosters?

It’s looking likely that we’re all going to need booster shots, Saxinger says.

It’s possible that people who’ve had two shots of AstraZeneca may end up having to get an mRNA booster, or even vice versa.

Most of the major vaccine makers are already testing new versions in case it turns out that protection wanes over time, or we end up needing a new version tailored to the variants.

One thing Saxinger finds interesting is the way in which the effectiveness of the AstraZeneca vaccine only seems to get stronger over time, at least for the first few months.

“It was not as quick out of the gate, but it was like a pursuit predator, it just kept on going and going.”

So we might end up finding out over time that each vaccine has different pros and cons in the long run, she says.

What’s going to happen to Canada’s AstraZeneca supply?

There are about 600,000 shots in fridges around the country, and Canada is entitled to millions more under our advance purchase agreement.

The country now faces a choice about whether to try to get them into arms or send them elsewhere, but experts are united in the opinion that they should be used.

As Saxinger puts it: “Having vaccines potentially go to waste in a situation where lots of countries don’t even have full coverage for front-line health care workers actually makes me feel ill.”

With files from Alyshah Hasham

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