Booster shots, 3rd doses and who needs them

As we approach the 11-month mark from when the first COVID-19 vaccinations were given in Canada, many people are wondering about whether and when they might need an additional dose to remain protected against the virus. That raises lots of questions. Here's what we know and what we don't.

What's the difference between a booster shot and a 3rddose?

The three approved COVID-19 vaccines in Canada (Pfizer-BioNTech, Moderna and AstraZeneca) are all two-dose regimens. A third dose is for people who may not have mounted a strong enough immune response to fight off COVID-19 after two doses.

The National Advisory Committee on Immunization (NACI) has identified two populations that require third doses: elderly people living in long-term care and those who have specific health conditions that make them immunocompromised (including organ transplant recipients). For these people, a third dose is an extension of their primary series of vaccinations.

A booster shot is for people who likely had a fulsome immune response to the regular two-dose vaccine regimen, but "with time, the immunity and clinical protection has fallen below a rate deemed sufficient in that population," according to the World Health Organization (WHO).

It's comparable to the tetanus vaccine, which requires a booster shot every 10 years. Most experts agree that everyone will likely need a COVID-19 booster shot at some point within the next year, but the big question is when.

Who is eligible for a booster shot?

On Friday Oct. 29, NACI issued new guidance "strongly" recommendingbooster shots for seniors 80 and older. It also said boosters "may" be offered to other groups that"may be at increased risk of lower protection over time since vaccination, increased risk of severe illnessor who are essential for maintaining health system capacity."

Those groupsinclude:

• Adults between the ages of 70 and 79.
• Anyone who received two doses of the AstraZeneca/COVISHIELD vaccine or one dose of the Johnson & Johnson/Janssen(J&J) vaccine.
• Adults in or from First Nations, Inuit and Mtis communities.
• Adults who are front-line health-care workers who have direct in-person contact with patients and who were vaccinated with a very short interval between their first and second doses (three or four weeks).

Booster shots should be given at least six months after the second dose of vaccine, NACI said. The boosters should also be one of the mRNA vaccines Pfizer-BioNTech or Moderna, it said.

AlthoughNACI makes recommendations,most aspects of health care, including vaccination, areunder provincial or territorial jurisdiction. Soit's ultimately up to the provinces and territories to decide who gets a booster shot and when.

Somemade their own decisions before NACI made booster recommendations. The Northwest Territories hasannounced anyone 18 years of age or olderwill now be eligible for a booster shot.

British Columbia has saidseniors age 70 and older, all Indigenous people 12 and older and health-care workers who only had three or four weeks between their two doses will all be able to get a booster shot by the end of the year. By next May, everyone in B.C. will be eligible.

WATCH|B.C. to offer COVID-19 booster shots to everyone by May:

B.C. to offer COVID-19 booster shots to everyone by May

3 years ago

Duration 1:53

After NACI's guidance on Oct. 29,the Ontario governmentsaid it would release its plan for COVID-19 boosters the following week.

Why would people who got 2doses ofAstraZenecaneed boosters?

Those who got viral vector vaccinestwo doses ofAstraZeneca(authorized in Canada) or one dose of J&J vaccine (a single-dose vaccine authorized in the U.S.) are on the list for a booster because evidence has shown they have "somewhat lower initial vaccine effectiveness" and people who got those shots"may become susceptible to infection sooner than people who received a primary series that included at least one dose of an mRNA vaccine," NACI said.

How do you know if 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.

One potential signal is an increase in breakthrough infections among people who have been fully vaccinated. That happened in some long-term care homes and was part of the reason why experts decided residents should get a third dose of the vaccine.

Booster shots should be given only to targeted populations where the science shows they're likely needed, WHO said in a statement in early October.

"The rationale for implementing booster doses should be guided by evidence on waning vaccine effectiveness, in particular a decline in protection against severe disease in the general population and in high-risk populations, or due to a circulating VoC [variant of concern]," WHO's statement said.

Right now, many experts say, most Canadians still have very good protection against COVID-19, including the delta variant.

"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.

Why doesn't Canada just offer boosters to everyone?

Health officials are trying to walk the line between giving third doses and boosters too early and giving them after people have already fallen ill, said Dr. Allison McGeer, an infectious diseases specialist and microbiologist at Sinai Health Systems in Toronto.

Because it's not yet known how long an effective immune response from the first two doses will last, health officials are trying to figure out the optimal time for a booster, so people get the longest-lasting protection possible out of each dose.

Another big reason, many health experts say, is "vaccine equity."Much of the world, particularly Africa, hasn't even received a first dose yet, according to WHO.

WHO has repeatedly pleaded with rich countries to stop giving what it considers unnecessary booster shots to people who are already protected against COVID-19, so those vaccines can be redirected to developing countries.

"We're planning to hand out extra life-jackets to people who already have life-jackets, while we're leaving other people to drown without a single life-jacket," Dr. Mike Ryan, head of the World Health Organization'shealth emergencies program, said during a news conference in August.

WATCH | WHO calls for halt on COVID-19 booster shots:

WHO calls for temporary halt on COVID-19 vaccine booster shots

3 years ago

Duration 1:45

Saying the priority should be on immunizing health-care workers in low- and middle-income countries, WHO director general Tedros Adhanom Ghebreyesus called for a temporary moratorium on COVID-19 vaccine boosters.

Many infectious disease and immunology experts agree that in addition to the ethical considerations, it's in Canada's best interest to help ensure people in developing countries get the COVID-19 vaccines they need.

That's because the longer the coronavirus that causes COVID-19 can circulate among unvaccinated people, the more likely it is to mutate into new variants that put everyone at increased risk.

"These vaccines are precious," Bowdish said. "If we want to make sure there's not the next variant and the variant after that and the variant after that, we really need to get the world vaccinated."

I keep hearing about 'waning immunity.'Does that mean I need a booster?

The term "waning immunity" usually refers to a decrease in antibodies over time. After any vaccination, immunologists and virologists say, it's normal for antibody levels to go down.

But the immune system is much more than antibodies.B cells and T cells are also hard at work. B cells produce antibodies and if they're exposed to the virus again, they "remember" and can make more. Tcells target and get rid ofinfected cells.

A study published in the journal Science found "robust cellular immune memory" from B cells for at least six months after mRNA vaccination against all circulating strains of the virus even the highly contagious delta variant.

Many experts agree that having waning antibodies does not automatically translate into a need for a booster shot.

After NACI'snew guidance on Oct. 29,Dr. Theresa Tam, Canada's chief public health officer, said it was "possible" that there could be a national recommendation for everyone to get COVID-19 boosters at some point but not now.

At this point, "aprimary series of the vaccines [still] provides good protection to the general public," she said, noting that boosters could be rolled out in a "phased approach" over time just as the initial vaccinations were.