Why doctors say COVID booster shots aren't for everyone yet

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Many Canadians are watching as countries like the U.S. and Israel authorize COVID-19 booster shots for more people and wondering why third doses aren't being widely recommended in Canada.

Israel is moving most aggressively,recommending boosters to everyone 12 years of age and older. In the U.S., everyone 65 years old and above is eligible for a booster, along with people with certain underlying medical conditions.

Canada's National Advisory Committee on Immunization (NACI) has so far only recommended third doses for people living in long-term care and people who have one of a handful of specific conditions that makes them moderately to severely immunocompromised.

Several people have been contacting CBC News to ask why those withchronic conditions that make them more vulnerable to severe illness if they get COVID-19 or seniors who don't live in long-term care aren't on NACI's list.

CBC News spoke to immunologists,infectious diseases specialists and a geriatrics expert to find out.

All agreed that everyone will need a booster at some point but for most people, that time isn't now.

"As of today, we're not seeing any risk that people who are vaccinated, outside of those special populations [identified by NACI] are having any waning immunity," said Dawn Bowdish, Canada Research Chair in aging and immunity and a professor at McMaster University in Hamilton.

The reason people in long-term care and those who have suppressed immune systems need a third dose, Bowdish said, is that "those folks never had a very good immune system to start with."

There are several other factors behind why seniors in long-term care needed a booster now, experts say, including the fact that they were among the first to be vaccinated, so more time has passed, and immunity can wane over time.

Boosting residents'immune systems to the best they can be is critical because they're also living in a congregate setting and coming into contact with various people, which puts them at greater risk of being exposed to the virus that causes COVID-19.

I have a chronic condition. Why am I not on the 'immunocompromised' list?

There's some confusion among people who are worried that their immunity to COVID-19 might not be sufficient, because they've been told that their chronic condition, including diabetes or heart disease, puts them at higher risk for severe illness if they become infected with the virus.

Experts say it's necessary to untangle two concepts: the risk of severe illness and the ability to mount an immune response when vaccinated.

"People should not make assumptions as to what their particular condition means in terms of their immune response," said Dr. Lynora Saxinger, an infectious diseases specialist at the University of Alberta in Edmonton.

"[For] a lot of people who are told that they have medical conditions that puts them at higher risk [for severe disease] that doesn't mean that another dose of vaccine is going to actually be helpful," Saxinger said.

"Asthma, diabetes, heart disease things like that, we don't worry about them making poor vaccine responses," Bowdish said.

For example, "diabetics tend to do really poorly with all infections, let alone COVID [but] diabetics make amazing responses to vaccines in general," she said.

"So those are folks that even though, yes, they would be susceptible to a poor outcome with infection, we have no concerns about them being vaccinated and not having good immunity."

According to NACI, the immunocompromising conditions that make someone eligible for a third dose are:

• Active treatment for solid tumour or blood cancers.

• Organ transplant recipients taking immunosuppressive therapy.

• People getting chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic stem cell transplant (within two years of transplantation or taking immunosuppression therapy).

• Moderate to severe primary immunodeficiency (e.g.DiGeorge syndrome, Wiskott-Aldrich syndrome).

• Stage 3 or advanced untreated HIV infection and those with AIDS.

• Active treatment with certain immunosuppressive therapies.

How do you know it's time for a booster?

Researchers, immunologists, infectious disease specialists, public health units and all levels of government are constantly looking for "signals" that would suggest immunity is waning in certain parts of the population.

"People are watching this really carefully daily, obsessively," said Dr. Allison McGeer, an infectious diseases specialist and microbiologist at Sinai Health Systems in Toronto.

One of the main signals they're watching for is an increase in breakthrough infections among people who have been fully vaccinated.

"We'd expect if that was happening [it] would be creeping up with the people who had been vaccinated a long time ago. And that signature is just not there," said Bowdish.

The other thing experts are monitoring is people's antibody levels after vaccination. That was one of the signals that led NACI to recommend that seniors in long-term care get boosters.

The tricky part, experts say, is determining how low the threshold needs to be before deciding a booster shot is required.

"It is completely common that after you get a vaccine your antibody level will be higher and then it will drop lower over time," Saxinger said.

"The real question is: What does your immune system do when it's exposed [to the virus]?"

That's because the immune system is complicated, made up of more than just antibodies. If you've been vaccinated, B-cells and T-cells also recognize the virus and fight it off.

The Canadian advantage

People shouldn't necessarily compare what's happening in the U.S. and Israel to the booster situation in Canada, Bowdish said.

"The Canadian situation is very different," she said. "We made a couple of gambles early on that have really paid off."

One is the decision NACI made last March to lengthen the time between first and second doses to a maximum of 16 weeks, compared to the three-week spacing recommended by Pfizer and four weeks recommended for Moderna.

"That increased length of time had actually been proven to be extremely beneficial," Bowdish said.

Preliminary research from the B.C. Centre for Disease Control and the Quebec National Institute of Public Health (INSPQ) have demonstrated an increased level of vaccine protection with the longer intervals.

Another Canadian decision to allow the mixing and matching of approved vaccines also proved to be effective, Bowdish said.

Experts suspect that the fact long-term care residents were vaccinated first before the guidance to extend the interval between doses came out could be one of the factors behind waning immunity in that group compared to seniors who were vaccinated later.

Who should be next to get booster shots?

Both infectious disease experts and immunologists have their eye on front-line health care workers as the potential next group to require booster shots.

Along with long-term care residents, health-care workers were among the first to receive their COVID vaccines, starting in December 2020.

That means up to 10 months have passed, so their immunity could be on the verge of waning. In addition, like long-term care residents, many of them received their two doses before increased spacing was recommended, so they won't have that extra protective factor.

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Dr. Lynora Saxinger, an infectious diseases specialist and associate professor at the University of Alberta, talks about why COVID-19 booster shots are recommended for some people and not others, and why there is no consistency across the country.

Some experts think seniors living outside of long-term care homes should be next to get boosters particularly if they are frail.

Many elderly people requiring home care "probably would be a good candidate for a booster," said Dr. Samir Sinha, director of geriatrics at Mount Sinai and University Health Network hospitals in Toronto.

With different care providers coming in and out, potentially increasing their risk of exposure to COVID-19, "they're literally living in a long-term care home of one," Sinha said.

"But right now I don't necessarily have the public health guidance and backing, or the guidance and backing of NACI, that I could actually successfully advocate for them to get a booster."

Part of the problem, both Sinha and Bowdish said, is that it's difficult to collect data on seniors at home and get the evidence needed to show if their immunity is waning or not.

Sinha worries that by the time the evidence is available that says boosters are warranted, they'll be competing with an enormous vaccination campaign for children under 12, once Health Canada approves vaccines for them.

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Next generation boosters

Right now, health officials are trying to "walk the line" between making sure people get third doses or boosters before they get sick, but not too much sooner than they need them, McGeer said.

That's because it's not yet known how long third doses will last, so timing is important to make sure people get the longest immunity protection possible.

In addition, there are many manufacturers working on the next generation of vaccine boosters, which experts hope will more precisely target variants.

"I'm fully expecting to get my third shot at some point, but I'm holding out and hoping that I'll get one of those variant-specific boosters," said Bowdish.

"Then [we can] use the current vaccines we have to target really vulnerable folks or people outside of Canada who are not getting vaccinated because they just don't have access to the vaccines yet."