Which COVID-19 booster shot should I get? Your questions answered

This story idea came from audience members, like you, who got in touch with us. Send us all of your questions about COVID-19. We are listening: covid@cbc.ca.

As the omicron variant continues to spread, many of you have been writing to us about COVID-19 booster vaccines.

We have been listening and posing your most-common questions to the experts. Here's what they have to say.

Am I eligible for a booster shot?

That depends on where you live.

Whether or not you will be offered a COVID-19 booster shot is based on each province or territory's eligibility criteria and rollout plan.

Earlier this month, the National Advisory Committee on Immunization (NACI) recommended mRNA booster shots be administered to all Canadians over the age of 50 and anyone who falls into the high-risk category, including health care workers, Indigenous people, residents of long-term care homes or those living in congregate care settings.

Anyone who received the AstraZeneca or Johnson & Johnson vaccines, at least six months out from the second shot, is also included in NACI's recommendation, which followed oneissued in September that recommended boosters for some immunocompromised individuals.

This announcement came amiddebate aroundeligibility expansion prompted by the new omicron variant. NACI's latest recommendation is giving provinces and territories the scope to widen the currently limited booster shot campaign.

Here's where you can find the eligibility criteria for booster shots in every province and territory as of December 2021:

• Alberta
• British Columbia
• Manitoba
• New Brunswick
• Newfoundland and Labrador
• Northwest Territories
• Nova Scotia
• Nunavut
• Ontario
• Prince Edward Island
• Quebec
• Saskatchewan
• Yukon

What booster should I get?

Right now, you have two options.

Health Canada has authorized Moderna's COVID-19 vaccine (also known as Spikevax) and Pfizer-BioNTech's vaccine (Comirnaty) for booster-shot use in people 18 or older. Both are mRNA vaccines.

The Moderna booster shot is a half dose. The Pfizer-BioNTech booster is a full dose.

So how do you know which one is best for you? According to the experts, it may not matter.

"We've got randomized trial evidence and real-world evidence that it really doesn't matter what booster you get or your third dose that you get," said Dr. Prabhat Jha, director of the Centre for Global Health Research at St. Michael's Hospital and professor of epidemiology at the University of Toronto.

Even if you received a viral vector vaccine, such asthe AstraZeneca or Johnson & Johnson shots, for your first two doses, getting one of the mRNA boosters that are available to Canadians will still offer strong protection against COVID-19.

Some experts suggest going from viral vector to an mRNA booster is not only safe but could even strengthen your immune response.

"We see from evidence all around the world that when you get vaccines of two different classes, it gives a bit of an extra boost of immunity," said Dr. Sumon Chakrabarti, infectious disease physician at Trillium Health Partners, a network of three health care centres in Torontoand Mississauga, Ont.

Does the booster help against the omicron variant?

Pfizer and BioNTech released a statement saying a three-course shot of their COVID-19 vaccine was able to neutralize the omicron variant in a laboratory test.

The companies have stressed their findings are "preliminary," with more research and data required,but said that two vaccine doses resulted in significantly lower neutralizing antibodies that fight the variant. They said a third dose of the vaccine increased the neutralizing antibodies by a factor of 25.

WATCH | Respirologist discusses new omicron laboratory findings

Pfizer-BioNTech say booster dose could neutralize omicron variant

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Respirologist Samir Gupta says while the laboratory findings for boosters are generally positive, we're still learning what it means for real-world protection against the omicron variant.

Blood samples obtained from people who had their third booster shot a month ago showed the omicron variant was neutralized about as effectively astwo doses fought off the original virus first identified in China.

But one of the caveats with this kind of information is that we don't have a threshold, said Dr. Samir Gupta, respirologist and associate professor at the University of Toronto.

"We don't have that straight line between a drop in neutralizing activity and what it means for real-world protection."

The companies saidthey would be able to deliver an omicron-based vaccine in March 2022if needed.

Though there are many unknowns, doctors and specialists are sticking to their bottom line: more protection is better than none. Dr. Christopher Labos is an epidemiologist in Montreal, and he predicts that a third shot will likely increase protection as the effects from first and second doses start to slowly wane.

"The point of getting a booster is to remind your immune system what COVID looks like so it keeps making antibodies against it," said Labos. "It is very conceivable that with the booster, you're going to have longer-term immunity."

And if you think you should wait for a new booster that's tailored to new and emerging variants, you might be making a risky decision. It could take months for a prototype to be developed and clinically tested.

"By then, probably the immunity that you have from the current vaccine would have waned to such an extent that you should have gotten the booster earlier," said Dr. Brian Conway, infectious disease specialist and medical director for the Vancouver Infectious Diseases Centre.

"So I would go for the booster, and then let's see what happens going forward with the subsequent shot for COVID 19, if and when it is necessary."

Do I need a booster even if I'm young, healthy and double-dosed?

Many younger and lower-risk Canadians have written to us wondering if they'll need a booster,too.

The first thing to consider is how long it has been since your last dose. A lot of people in this age group may not have been vaccinated until late summer and won't be eligible until six months have passed.

Once you do become eligible for a booster shot, Jha says it's important to follow local public health guidelines and get a jab.

However, he did acknowledge that booster shots for young people are not as urgent as they are for people in higher-risk categories.

Labos agreed, saying it's a matter of timing for young people.

"If you're young and healthy and got vaccinated relatively recently, it's not an emergency for you to get a booster shot now."

He says there are no issues with getting a booster if you're young and healthy but that it could impactvaccine equity.

"We don't want to be wasting doses on the population here in Canada when we can put those to better use."

WATCH | Toronto infectious disease specialist says get vaccines to everyone around world:

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Dr. Isaac Bogoch says it's important to understand the new coronavirus variant, and equally important to get people around the world vaccinated. (Credit: AP Photo/Tsvangirayi Mukwazhi)

What if I don't want an mRNA vaccine?

If you don't want to getan mRNA vaccine as a booster, you may eventually be able to get another dose of a viral vector vaccine. However, the National Advisory Committee on Immunization (NACI) has yet to approve viral-vector vaccines as booster shots.

Dr. Gerald Evans, an infectious disease specialist at the Kingston Health Sciences Centre, said in an email that there are virtually no valid medical reasons why someone couldn't receivethe current mRNA vaccines.

"Any prior reactions can be easily managed with help from allergists and the use of pre-medications."

The approved viral-vector COVID-19 vaccines that were approved for use in Canada are the AstraZeneca, COVISHIELD and Janssen vaccines.

Under NACI's guidelines, people who have received a viral-vector vaccine should getan mRNA booster shot if they can because viral-vector vaccines are less effective than their mRNA counterparts.

Evans noted that the not yet released recombinant subunit vaccines, such as Novavax, could be an alternative but it is still under review by Health Canada.