Health Canada is expected to make a decision on the AstraZeneca/Oxford University COVID-19 vaccine any day with an extra 1.1 million doses to be delivered by the end of March pending that approval. Several European nations are already discouraging its use among seniors, citing a lack of data.
When asked about the efficacy in older adults the day before, Canada’s deputy chief public health officer Dr. Howard Njoo said that Health Canada will review the data as it becomes available.
Earlier this week, AstraZeneca reported that a primary analysis of its Phase 3 trials showed an overall efficacy rate of 76 per cent after the first dose and 82 per cent after the second.
The company said that its adenoviral vector vaccine may also reduce transmission of the virus.
The two vaccines currently approved in Canada, the Moderna and Pfizer-BioNTech mRNA vaccines, both have efficacy rates around 95 per cent.
“We’ve been spoiled, our expectations have been set at that really, really impossibly high level and everything else is a disappointment,” said Dr. Alan Bernstein, CEO of CIFAR and member of the federal COVID-19 Vaccine Task Force.
“But, you know, 75 per cent is pretty good in real life.”
AstraZeneca’s vaccine was authorized for emergency use in the U.K. at the end of December, and in Argentina, the Dominican Republic, El Salvador, Mexico and Morocco early this year, before being approved for all adults by the European Medicines Agency (EMA) at the end of January.
France, Sweden, Germany, Italy, and Poland have all issued recommendations stating the vaccine should be prioritized for adults under the age of 65, 60 — or even 55 in the case of Italy — according to Politico Europe and France 24.
In its decision, the EMA said most of the participants in AstraZeneca’s trials were between 18 and 55 and it needed more results in older participants “to provide a figure for how well the vaccine will work in this group” but it went on to say that “protection is expected.”
Director of geriatrics at Sinai Health System in Toronto, Dr. Samir Sinha, said his view is that Canadians should “get the vaccine that you can get your hands on as soon as possible because as soon as most of us are vaccinated, the more community protection we have and the better off we’re all going to be.”
Bernstein echoed those sentiments, adding “they all look very effective.”
He also explained that efficacy is just one factor — though a very important one — in deciding what makes a good vaccine.
The science of vaccines
What is vaccine effectiveness?
Vaccine effectiveness and vaccine efficacy are actually slightly different, as explained by Bernstein.
Efficacy refers to the results from a controlled trial whereas effectiveness reflects how it performs in the “real world,” though both terms tend to be used interchangeably outside of academic settings.
“The reason it’s distinguished from a trial is trials are not in a sense ‘real-life’ in that the companies will choose volunteers that are healthy beforehand or try to choose volunteers that are healthy beforehand,” he explained.
He said it’s not that companies are “fudging the results” but that they don’t want results to be “confounded by people who are already very ill.”
So, how is efficacy determined?
In Phase 3 of a vaccine trial, scientists compare the results from a group of people who’ve received the vaccine to a group of people who have received a placebo.
“If 100 people got infected in the non-vaccinated group, we then looked over to the vaccinated group. We say, ‘OK, well, if all these people were circulating in the same community, there should be at least 100 people who could have gotten infected in the vaccinated group,’” Sinha explained.
“And when we find out that only five actually got infected, it tells us then that that vaccine is 95 per cent effective.”
Sinha adds that 95 per cent effectiveness, for example, doesn’t mean that 95 people out of 100 people are protected, but rather that “it’s up to 95 per cent effective in every one of us who gets that vaccine. We just don’t know who might be the person, for example, who doesn’t have that level of effectiveness.”
“If we give you the vaccine, can your body respond to that vaccine to give you the protection that you need to fight off COVID?”
What impacts vaccine effectiveness?
The same weakened immune system that makes the elderly more susceptible to the virus is also what makes them less likely to have a robust response to vaccines.
“We’re all different genetically, which means we have different responses genetically in our immune system to insults like viruses. And some people overreact, some people underreact, and some people are in the sweet spot of reacting just right,” Bernstein explained.
“It’s possible that different ethnic groups, that people of colour, will respond differently to the virus or to the vaccine or both. And that has not been studied that carefully actually, yet.”
While everyone’s immune system is a little bit different, Sinha says typically young and healthy people have a “good, robust immune system.” Age or illness, for example, can weaken the immune system.
The fact that the Moderna and Pfizer vaccines appear to be as effective in older people as in younger people actually surprised Sinha.
“It must be this mRNA technology that actually helps to boost the immune systems of older people in such a way that they get the same level of protection as younger people,” he suggested.
“What we might see over time is other more traditional vaccine technologies, they may not be able to boost the immune system of older people or other more immunocompromised people to the same level.”
It’s possible, Sinha says, that we may get to a point where health care professionals would select a vaccine based on how well a particular person is likely to respond to it.
“And right now, for my older patients, I would highly recommend they get the Moderna or Pfizer vaccination because they seem to be 95 per cent effective.”
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What else makes a good vaccine?
Outside of efficacy in preventing illness, Bernstein says the two other properties that matter are how long protection lasts and what impact the vaccine has on transmission.
“So let’s say you have two vaccines, one’s 70 and one’s 90 per cent effective in the trials, but the one that’s 70 per cent lasts for five years, the one that’s 90 only lasts for six months,” he said as a hypothetical example.
“Which is a better vaccine?”
Sinha says that vaccines approved so far have been shown to significantly protect people from getting sick and dying but more data is needed to determine “if it can actually prevent your ability to transmit the virus to another person.”
Data released earlier this week from AstraZeneca showed that the viral load “in the body of people who were vaccinated is lower than in the placebo group,” which Bernstein says would be “consistent but not proof that it may be transmission is lower from person to person.”
In addition to the Pfizer and Moderna vaccines, Bernstein expects that the AstraZeneca, Novavax, and Johnson & Johnson/Janssen vaccines will be approved in Canada.
“And that’s not meant to influence Health Canada because I can’t. But that’s my own view, looking at the data — and the regulators will see more data than we have seen, than I have seen. They’ll see every little scrap of data,” he explained.
“There may be things there that are, you know, deal-killers. But I think based on what we know and what the companies have released, I would say that all three will be approved.”
— With files from Global News’ Emerald Bensadoun and Reuters.
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