Arabnews24.ca:Saturday 23 October 2021 04:19 AM: This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed to subscribers every Saturday morning. If you haven't subscribed yet, you can do that by clicking here.
Canadians concerned over waning immunity from COVID-19 vaccines, breakthrough infections and the need for booster shots in the general public could benefit from a dose of some important context, experts say.
Antibodies, your first line of defence against COVID-19 infection, do decline — and may even be doing so as you're reading this — but that's not unexpected.
While one aspect of your vaccine-induced immunity to COVID-19 is technically "waning" in the weeks and months after vaccination, that's not necessarily a bad thing — because it's not your immune system's only form of protection against the virus.
"I don't even like the term," said University of Toronto immunologist Jennifer Gommerman. "And the reason I don't like the term is that it implies that the immune response in its entirety is declining."
It's "entirely normal" for antibody levels to drop initially after vaccination and your immune response to the virus to become "contracted" over time, she said. But your body is also creating "highly efficient" memory B cells to fight off COVID-19 long term.
B cells work quickly to generate large quantities of antibodies in the weeks after vaccination, but they typically produce more effective antibodies as time goes on, helping sharpen the long-term response to a virus.
So while reports of waning immunity may sound concerning, that initial decrease in antibody levels may also be necessary in the fight against COVID-19, as it helps fine-tune the immune system's plan of attack.
A new 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.
The researchers found those memory cells, unlike the initial wave of antibodies, continue to learn how to fend off the virus months after vaccination and are actually getting better at it over time.
"That doesn't sound like 'waning' to me," Gommerman said. "There's a natural contraction, but waning implies that something bad is happening."
Breakthrough infections don't tell the whole story
Reports of waning immunity and breakthrough infections have sporadically emerged across Canada in places like the Northwest Territories and New Brunswick, but lack important context and data on who is seriously affected and why.
The N.W.T. has been in the midst of a COVID-19 outbreak since mid-August that started in the Sahtu region before spreading to Yellowknife and its surrounding communities. It has infected 1,584 residents.
During that time, there have been 54 hospitalizations attributed to the outbreak, about 17 of which were among fully vaccinated people. A government spokesperson declined to comment on how many of the nine deaths in the territory were among those fully vaccinated.
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In New Brunswick, where reports that one in five COVID-19 deaths occurred in people who were fully vaccinated made headlines this week, the data shows that while 17 fully vaccinated people have died, evidence of widespread waning immunity is lacking.
"New Brunswick has not identified confirmed evidence of waning immunity among COVID-19 cases," a government spokesperson said in a statement.
In terms of national numbers, 94.7 per cent of all COVID-19 cases in Canada since Dec. 14 have been among those not fully vaccinated, as well as 95.8 per cent of hospitalizations and 94.3 per cent of deaths, according to the Public Health Agency of Canada (PHAC).
That means a total of 520 fully vaccinated Canadians have died of COVID-19 in the nearly 10 months since our vaccine rollout started, compared with 8,520 who were not considered fully vaccinated during that same time period.
"If we have 100 per cent or 95 per cent of the population vaccinated, almost all the cases that we see, including severe cases, will be in vaccinated people — just because most everyone's vaccinated," said Dr. Lynora Saxinger, an infectious diseases physician and associate professor at the University of Alberta.
"So that very rare outcome becomes the majority of the outcomes, and seeing an increasing number of cases in vaccinated people over time doesn't actually mean that the vaccine works less well, necessarily."
Underlying conditions key to breakthrough infections
PHAC says fully vaccinated Canadians who do get COVID-19 are also 79 per cent less likely to be hospitalized and 64 per cent less likely to die, backing up new Canadian data showing strong vaccine protection from infection, hospitalization and death.
But key information on the age, underlying health conditions or specific vaccine combination administered to those who were hospitalized or died from COVID-19 two weeks after their second shot is not available in Canada due to health privacy laws.
The recent death of former U.S. Secretary of State Colin Powell from COVID-19 sparked fresh debate about breakthrough infections and waning immunity. But less attention was paid to the fact he was at heightened risk due to a blood cancer called multiple myeloma.
Older, frailer Canadians living with comorbidities in congregate settings, such as long-term care facilities, are at increased risk of breakthrough infections because their antibody levels drop "much faster" than in the general population, said Gommerman.
A recent preprint study from the Toronto-based Lunenfeld-Tanenbaum Research Institute at Sinai Health analyzed 119 Ontario long-term care residents and 78 staff over four months, finding much lower levels of neutralizing antibodies in the elderly patients.
Gommerman also stresses there's an important difference between infections and disease.
"We expect people to get infected — even healthy people to get infected — as antibody levels decline, because the only thing that can protect you against a breakthrough infection are antibodies," she said.
"But we have to think about who we're looking at, and what underlying comorbidities might be there in people who experienced breakthrough disease."
Other immunocompromised groups, such as transplant patients, have shown declining protection from COVID-19 vaccines, as evidenced in the New England Journal of Medicine from researchers at the University Health Network (UHN) in Toronto.
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"If you are a healthy person and you've been fully vaccinated, you don't need to worry about getting severe COVID-19," Gommerman said.
"If you are worried about getting infected with SARS-CoV-2, you should worry because you have people around you who are not vaccinated or who are under-immune."
Boosters for general population 'premature' in Canada
New data from researchers at the Institute for Clinical Evaluative Sciences (ICES) in Toronto, which has not yet been peer-reviewed, found fully vaccinated people over 16 in Ontario were highly protected against both infection and severe COVID-19 after eight months.
ICES's vaccine estimates, which have not yet been published, show that protection against symptomatic infection does drop — from 94 per cent to 81 per cent — but protection against severe outcomes remained high, at more than 90 per cent.
"The main takeaway is that we don't need to do boosters at this time for the general population. We can hold off and wait and see — and when we start seeing the waning, then that's when we should use the boosters," said Dr. Jeff Kwong, an epidemiologist and senior scientist at ICES.
"It would be premature to do it at this time and not in our best interest, because we're allowing other variants to emerge potentially if we let the pandemic spread uncontrolled in other parts of the world [where] they're not vaccinated."
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Saxinger said the vast majority of Canadians who get severely ill or hospitalized after full vaccination are the very elderly, the immunocompromised, transplant patients and people with certain types of cancers.
"That group of people, of course, they should get a third dose," she said. "But even with a third dose, they still are going to remain vulnerable as long as we have circulating virus in the community."