Predictions of a fall wave of COVID-19 make a new booster vaccine campaign likely, but questions abound about how the virus will continue to evolve and what protections a new vaccine might offer.
Several vaccine makers are racing to develop formulas that take into account the more infectious Omicron variant, which is now leading to cases as policymakers lay the groundwork for another large-scale vaccine blitz.
Much of that hinges on expectations that the so-called bivalent shot could blunt a potential future spike as flu season approaches and ease pressure on a strained health care system.
The National Immunization Advisory Committee last week released interim guidance for a fall program that it says is most important for older people and those at increased risk of severe COVID-19. He also noted that while the vaccine’s protection against symptomatic disease wanes over time, protection against severe disease is better maintained.
In the United States, advisers to the Food and Drug Administration said last week that fall boosters should contain some version of the Omicron variant.
NACI stopped short of pushing for a specific formulation pending more evidence, but said a bivalent injection may promote absorption in the fall.
Here’s a look at the next stage in the fight against COVID-19.
WHAT ARE BIVALENT VACCINES?
Currently available vaccines against COVID-19 are monovalent – tailored only to the original novel coronavirus. The proposed bivalent vaccines target specific mutations in the spike protein seen in both the old strain and the newer Omicron strain, which itself has given rise to several more infectious subvariants dominating infections today.
Essentially, bivalent vaccines are a split between the old “original” mRNA sequence and the new sequence, says infectious disease specialist Dr. Zane Chagla.
“So, for example, Moderna’s bivalent vaccine is 25 mcg old vaccine, 25 mcg updated vaccine,” he says.
The basic principle is already well established with the flu vaccine, says immunologist and University of Toronto professor Tanya Watts.
“For the flu, we do three or four different options. It’s just a mix and RNA vaccines are very easy to mix and match. In theory, we could have 10 (targeted variants),” says Watts.
“And I really think that’s the future. People are striving to get a universal vaccine.
IS FALL TOO LATE FOR THE OMICRON VACCINE?
Experts say Canada is already in the midst of its third Omicron wave, which could be followed by a new threat from the COVID-19 variant, but that doesn’t necessarily mean the Omicron-modified vaccine is out of date if it doesn’t land by fall.
Dr. Volker Gerdts, director and CEO of the Vaccine and Infectious Diseases Organization, says the best strategy is to provide protection that is as broad as possible.
“That’s why some of these so-called bivalent vaccines still have the original strain in them, and then an extra Omicron or Delta with it,” says Gerds.
“The whole point is to have multiple different types in your vaccine to provide broad protection.”
Part of the difficulty in evaluating new vaccines is evaluating them against variants that don’t even exist, he says.
“If we have in this vaccine a representation of many different strains or different variants, then we can assume that we are getting broad protection against future variants as well,” he says.
Pfizer Canada and Moderna Canada say their mRNA platforms allow for rapid updates to address new variants if needed.
But it’s possible that “bivalent boosters can provide broad protection against several different variants, even ones they’re not specifically designed to fight,” Shehzad Iqbal, medical director of Moderna Canada, said by email.
WHAT CAN BIVALENT VACCINES DO?
There’s some uncertainty here, says Chagla, a professor at Hamilton’s McMaster University.
The evidence so far is that they can raise antibody levels more than previous doses. But he says there is no clinical data illustrating exactly what this means: Does it mean longer protection against symptomatic disease? Even more protection against hospitalization? How long do the effects last? Will they decrease over time?
“There are no guarantees with this booster coming in,” says Chagla.
“My guess is that it will probably extend benefits for a symptomatic infection beyond eight weeks, nine weeks, 10 weeks.”
He suspects they will behave in much the same way as current vaccines against COVID-19: the antibodies induced will decay over time and people may be reinfected.
Things are complicated by the fact that the virus continues to evolve, adds Chagla.
WHEN WILL THEY ARRIVE?
Moderna Canada says it submitted its bivalent booster candidate to Health Canada on June 30 for regulatory approval. Iqbal says the proposed update is a 50 mcg dose that contains the original vaccine, known as Spikevax, and a candidate vaccine targeting Omicron.
“While we cannot speculate on the timing of Health Canada’s review, our goal is to have the bivalent booster containing Omicron available for early fall 2022,” says Iqbal.
Pfizer Canada also said it plans to seek approval for another COVID-19 vaccine.
“We are currently in discussions with Health Canada in preparation for providing our available data, including data for constructs that include Omicron BA.1 or BA.4/5 sub-variants,” the company said via email.
WHAT ARE THE CHALLENGES?
If the bivalent vaccines are ready for the fall, infectious disease expert Dr. Isaac Bogoch expects we could be running three concurrent vaccination programs: a booster program, a COVID-19 vaccine program for children under six, if they are also approved; and the annual flu vaccine program.
“One of the challenges is that in much of the country, much of the infrastructure for mass vaccination has been removed,” says Bogoch, a professor at the University of Toronto.
“Vaccines are now mostly administered in traditional settings such as primary care and public health clinics and pharmacies. So it’s probably going to be a very busy time.”
Chagla adds that there are a lot of moving parts to ensure a smooth rollout of the vaccine, as seen in the difficult days of Canada’s first big push to put needles in guns: “It’s not as simple as the vaccine drops and everyone has access, right?’
“You have to scale up, and that often takes people away from their day jobs, doctors away from their patients, and nurses and other valuable health care staff,” says Czagla.
Such campaigns should be timed to meet the increased risk of infection, he adds, making fall probably the best time to supplement population immunity, before increased indoor gatherings and seasonal gatherings.
WHAT NEXT?
Bogoch and Czagla point to steady advances in technology that could shape the coming years, including work to develop needle-free intranasal vaccines.
“And that could be very promising because it really focuses on what’s called the mucosal immune system.” And that may allow us to better prevent infection in the first place,” Bogoch says.
Together with Gerdts, they also promoted efforts to create pan-corona vaccines that can generate protection against multiple types of coronaviruses.
Gerds says such a product would likely include structures from many different members of the coronavirus family — not just SARS-CoV-2, which causes COVID-19, but also perhaps Middle East Respiratory Syndrome, also known as MERS, and another common respiratory coronavirus.
“The more distantly related members you have in your vaccine, the broader the level of protection against new variants that arise from them,” said Gerdts, who was scheduled to attend a meeting in Washington on Thursday and Friday, partly organized from the National Institutes of Health will decide how to protect against future variants.
“If a virus mutates and evolves further, it has to start somewhere and so if you go with these existing ones – but pick some that are very far apart so you’ve already evolved quite a bit – chances are you’ll catch all these new ones mutants that may appear in between.”
Such a vaccine is still years away, he adds.
“A lot of it is actually about predicting today what tomorrow’s pathogen might be.”
This report by The Canadian Press was first published on July 7, 2022.
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