Bivalent booster shots can help the human immune system recognize new COVID-19 variants, two new studies suggest, but it may not offer protection against all future strains.
“When you see another variant, your immune system should be able to recognize it, whether you have been vaccinated by something related to it or you actually became infected by it,” Dr. Donald Vinh, an infectious diseases specialist at McGill University Health Centre, told Global News.
However, it “doesn’t necessarily mean you’re going to be protected from everything downstream,” he added.
This is because no one knows what kind of new variants are going to emerge in the long run and what impact they’ll have on the human immune system, according to Vinh.
“I think all we can [comment on] for the moment is whether or not the vaccines are effective for the current variants,” he said, noting that the bivalent ones are.
The studies published in the bioRxiv preprint server in September suggest that a booster shot or breakthrough infection can help develop B cells (in humans) that create antibodies to recognize a broader range of strains and not just the one introduced by the vaccine.
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But Vinh emphasizes that the findings of the two studies shouldn’t make people assume that if they take the bivalent booster, they’ll be able to fight off whatever variant comes up in the future. The body can merely identify them better, he explains.
“We have to be careful. We have to learn from our previous pandemic mistakes. And one of them was that … if you get your vaccines, we will get the pandemic under control. And that was obviously not the case,” said Vinh.
“So, we can’t say that if you get a bivalent booster dose, you don’t have to worry about variants down the road. That’s not what the data says,” he added.
But the Omicron boosters do work, Vinh said, “to boost and broaden” the immune system.
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After the Omicron variant became the dominant strain in North America and the world, several vaccine manufacturers raced to develop bivalent boosters designed to target Omicron’s BA.4 and BA.5 subvariants.
In October, Health Canada approved Pfizer’s updated Omicron booster shot, which makes it the second bivalent vaccine to get federal approval after Moderna’s modified booster was authorized for use last month.
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But the “usefulness” of these boosters “has been called into question by recent data on a phenomenon known as immune imprinting,” according to the Nature Journal where the two studies are referenced.
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The studies were published last month. Neither has yet been peer-reviewed.
“Up until now we only had the monovalent mRNA vaccines that target the ancestral COVID-19 strain… the B cells saw the vaccine and learned to recognize the monovalent ancestral strain and people were worried that if you do too much of the monovalent vaccine then you get what’s called immune imprinting,” said Vinh.
Imprinting, “also called ‘original antigenic sin,’ refers to the immune system’s tendency to fixate on the first version of a pathogen that it encounters, regardless of subsequent attacks by different variants,” according to Nature Journal.
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Vinh likens immune imprinting to a car stuck in a muddy swamp with the concern being that “you’re spinning the wheels and creating a rut that you can’t get out of.”
“Immune imprinting is seeing the same antigen over and over again and you’re getting really good at recognizing only that and not recognizing other things,” said Vinh.
Because of the potential impact of imprinting, the Nature Journal said, “the immune system’s reaction to bivalent boosters has… been unclear.”
To find out if B cells are adapting or not, immunologist Ali Ellebedy at Washington University in St. Louis, Missouri, and his team conducted a study funded by Moderna.
The findings were published in the first preprint called ‘SARS-CoV-2 Omicron boosting induces de novo B cell response in humans.’
Ellebedy’s team collected lymph-node samples from 26 people and bone-marrow samples from 15 people; all had received the original vaccine and Moderna’s booster against Omicron BA.1.
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According to Nature Journal, the analysis showed that most of the participants’ B cells recognized both the original and Omicron strains. The participants also had a few new types of Omicron-specific B cells.
“These responses implied that the cells had overcome imprinting and adapted to a new strain,” the journal stated.
This provides some reassurance on the benefit of the bivalent shot and sheds light on the nature of the human immune system, Vinh noted.
“Your immune system won’t be paralyzed because of your previous vaccines,” said Vinh.
Shane Crotty, a virologist at the La Jolla Institute for Immunology in California, said in an article in Nature Journal, published on Oct. 14, that “the papers are both reassuring, showing that the immune system can be just as creative as the virus.”
“The immune system has [had] millions of years to realize that if one virus shows up, there’s a decent chance that in the near future some relative of that virus will show up,” Crotty said.
“Having a diversity of ways to respond is of value.”
In the ‘Evolution of antibody immunity following Omicron BA.1 breakthrough infection‘ preprint, Nature Journal said, “scientists collected samples from six people who became infected with Omicron despite having received the original vaccine.”
The team found that one month after an Omicron infection, nearly 97 per cent of participants’ antibodies targeting SARS-CoV-2 still fought the original strain better than Omicron BA.1. But six months after infection, nearly half of participants’ B cells produced antibodies that were able to fight Omicron BA.1 better than the original strain, “showing that the immune system continued to adapt long after the infection had passed.”
“It’s good to see evidence that, even when it’s imprinted, the immune system is adapting in ways that are helpful in redirecting to the newer variant,” said Jesse Bloom, a computational virologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington, who was a co-author on the second paper.
-With files from The Canadian Press
