WILL 3rd DOSE BEAT 4th WAVE?
For now, COVID-19 booster shots not used in Canada
The possibility of a Delta-driven fourth wave of COVID-19 and the emergence of breakthrough infections have some vaccinated Quebecers wondering if and when they will need a booster shot.
Quebec is expecting to receive its final vaccine shipment next week, bringing its reserve up to more than two million. Some of that stock will be kept for vulnerable people who may require boosters in the future, the Health Ministry announced Wednesday. Some countries, including Germany and France, have announced they will be administering third shots to those groups imminently. Israel has already begun giving third doses to those at risk.
But it has yet to be determined whether booster shots will be recommended in Canada, according to experts, because it's still unclear how long immunity from the first two doses lasts — and just how much protection is actually required for adequate immunity.
“The importance of boosters for people who are of usual health, I don't think we have the science to fully answer that question yet,” said Dr. Matthew Oughton, an infectious-diseases specialist at the Jewish General Hospital. “If it turns out that we need boosters, I think it's most likely we're going to need boosters in a subset of the population — probably people who are immunocompromised because of certain diseases or because of certain medications.”
Immunocompromised people and other vulnerable groups don't have as strong an immune response to the first two doses of the vaccine, which is why they could potentially need a third shot.
“It will be very selective,” said Dr. Donald Vinh, an infectious-diseases specialist and medical microbiologist at the Mcgill University Health Centre.
“It's not going to be: `Everybody who's already been fully vaccinated, line up again — you're going to get a third dose.' That's for sure not what's going to happen.”
Vinh, like Oughton, said there's still a lot to figure out in terms of immunity to COVID-19.
“We do know there are some people who have some conditions … where they don't respond well to the vaccine,” he said. “We still don't know exactly what that means because there's no threshold that says, `OK, if you're above this (level) you're protected; if you're below that, you're not protected.' We don't have those thresholds yet.”
On Thursday, Dr. Theresa Tam, chief public health officer of Canada, said Canada is continuing discussions on the potential need for booster shots and that evidence is still evolving.
“We've certainly seen publications from companies even today that of course the vaccines have remained quite effective for at least six months after the initial vaccination,” she said.
Vinh said there's a misunderstanding surrounding how antibodies work, which could be contributing to the confusion around the need for boosters.
“When people say, `When you give people two shots of a vaccine their antibody levels (eventually) go down and therefore we need to boost it' ... that's not how it works,” he said.
“We know for any vaccine — whether it's COVID or hepatitis B or even tetanus — that your antibody levels don't stay up permanently, nor should they. … There is a blip up, and then once your body realizes, `Well, this is not a constant threat' … it will quiet down and the levels go down, but the memory is there. So that if (your body comes into contact with the virus) again, you can respond rapidly.”
On Wednesday, the World Health Organization called for a moratorium on booster shots at least through September, given the gap in vaccination rates between high-income and low-income countries.
“I understand the concern of all governments to protect their people from the Delta variant,” said WHO director general Tedros Adhanom Ghebreyesus, “but we cannot accept countries that have already used most of the global supply of vaccines using even more of it.”
As of Friday, approximately 50 million doses of COVID -19 vaccine have been administered in Canada, more than 11 million of which have been given out in Quebec.
Canada announced on Wednesday it will be sending 82,000 doses of the Astrazeneca shot to Trinidad and Tobago. In its latest update on the vaccine campaign, Quebec said unused doses set to expire at the end of October will be given back to the federal government, which could send them overseas as needed.
Prativa Baral, an epidemiologist and a PHD student at Johns Hopkins Bloomberg School of Public Health, said it makes sense to think about boosters for the immunocompromised, but that it's important to have a wider approach to the vaccine rollout in order to see the end of the pandemic.
“I think we need to be thinking about vaccine equity more globally because as long as this virus is circulating somewhere, the risk of yet another variant emerging and completely evading the vaccine protection we currently have is a very real fear,” she said.