Why rushing COVID-19 booster shots for everyone could do more harm than good

This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed tosubscribers every Saturday morning. If you haven't subscribed yet, you can do that by clickinghere.

Canadians may be eager to get a third dose of COVID-19 vaccine to further protect themselves in the fourth wave, but the lack of evidence in favour of booster shots for the general public and the desperate need for vaccines worldwide should give us pause.

The World Health Organization recently called for a moratorium on boosters until at least the end of September, but rich countries are forging ahead with plans for additional doses now regardless including parts of Canada.

Israel has made third doses of COVID-19 available to everyone aged 30 or older, while the U.S. plans to offer boosters to anyone eight months out from their second shot on Sept. 20.

Other wealthy nations with ample vaccine supply have taken a slightly more nuanced approach, with France, Germany and the U.K. announcing third doses only for vulnerable populations at heightened risk of declining COVID-19 immunity.

But the European Centre for Disease Prevention and Control (ECDC) health agency said Wednesday there is no need to rush out booster shotsfor the general public because all authorized vaccines are highly protective against hospitalization, severe disease and death from COVID-19.

Now, with more than 67 per cent of our total population fully vaccinated, the question of whether Canada should be giving third doses to everyone eligible to better protect against delta is on the table as other wealthy nations begin to roll out boosters to the general public.

Do Canadians need boosters now?

Canada's National Advisory Committee on Immunization (NACI) is currently weighing the available data on the benefits of booster shots, and is expected to issue guidance soon. But Ontario and Alberta have already begun rolling them out to the immunocompromised.

"There are categories of people that don't make a great response to the vaccine," said Dr. Zain Chagla, an infectious diseases physician at St. Joseph's Healthcare Hamilton and an associate professor at McMaster University.

"Those at the extremes of elderly age, those who have major immunocompromising conditions, where absolutely a booster right now probably makes sense."

Canadian researchers at the University Health Network (UHN) in Toronto recently published a correspondence in the New England Journal of Medicine that showed evidence of "significantly higher immunogenicity" in transplant patients after a third dose.

And a recent preprint study, which has not been peer reviewed,from the Lunenfeld-Tanenbaum Research Institute at Sinai Health in Toronto analyzed 119 Ontario long-term care residents and 78 staff over four months, found much lower levels of neutralizing antibodies in the elderly patients suggesting a possible need for a third dose in that group as well.

"But then it turns into what do you do with the general population when studies have suggested that there is still significant protection?" Chagla said.

"There really hasn't been any data suggesting that getting a booster is really going to change their clinical picture."

Delta-specific booster 'better' for Canadians

As other countries rush to roll out third doses to the general public despite a lack of concrete, long-term data experts say it may be more advantageous to wait for the development of a delta-specific booster to directly target the variant.

Both Moderna and Pfizer-BioNTech are currently working on updated mRNA vaccines specifically tailored to emerging variants, but the third doses that are being rolled out in wealthy nations now are essentially additional shots of the original vaccine formulation.

But the development, testing and approval of a new shot will take time something not all experts agree we have.

Dr. Anthony Fauci, director of the U.S. National Institute for Allergy and Infectious Diseases, said Friday that three doses of the COVID-19 vaccines are likely needed for full protection, citing two Israeli preprint studies that showed a 10-fold decrease in serious illness for those over 60 and a marked reduction in the odds of testing positiveafter three shots.

But the data are limited in scope and experts point to the greater need for delta-specific booster shots for the general population, as opposed to third shots of the same formulation, in order to target the devastating variant.

Dr. Allison McGeer, a medical microbiologist and infectious disease specialist at Toronto's Mount Sinai Hospital, says there are two core reasons why developing a booster that specifically targets delta would be advantageous.

"One is it gives you better antibody levels against delta," she said, which could provide better protection against initial infection and onward transmission from the variant.

The second involves something called "imprinting," where your first experience with a virus or vaccine determines the nature of your immune system's response.

"If we're going to have delta as the new big thing, and your immune system is initially responding to [the original strain], then that would not be ideal," she said.

"It might be better to particularly for kids vaccinate them against delta."

Alyson Kelvin, an assistant professor at Dalhousie University and virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious Disease Organization in Saskatoon,says it's also more advantageous to wait until antibodies begin to fall before providing an additional dose so rushing boosters now may not make sense.

"I don't think there's data to support, in healthy adults, that there is going to be a substantial beneficial effect. You might see a rise in antibodies, but also your antibodies might be at their limit already so a boost might not do anything," she said. "Timing is important."

Until we have more comprehensive real-world data, experts sayif Canada is going to roll out boosters than we should start and stop with immunocompromised groups and the elderly for now.

"If the question is asked today, do we all need booster shots? The answer is no, we don't," said Dr. Isaac Bogoch, an infectious diseases physician at Toronto General Hospital and a member of Ontario's COVID-19 vaccine task force.

Future variants pose unseen threat

Without a doubt, the emergence of highly contagious coronavirus variants has been one of the biggest challenges to ending the pandemic in Canada and around the world.

New variants have repeatedly surfaced throughout the pandemic in populations with low vaccine coverage that have been hit hard by unchecked COVID-19 transmission including India, South America and Africa.

The devastation caused by the original strain of the virus from Wuhan, China was overtakenby the emergence of the highly contagious alpha and beta variants in late 2020, which drove Canada's brutal third wave and set off a mad rush to get people vaccinated.

In the spring, Canada became one of the only countries in the world with significant outbreaks of three different variants occurring at the same time,turning us into a giant experiment on the world stage.

But the delta variant completely changed the battlefield, quickly usurping all other variants to become the dominant strain in Canada by the summer and fuelling a worsening fourth wave at a time when many thought the pandemic would be winding down.

Experts say the shortsighted approach of providing third doses to everyone, based largely on preliminary data and unproven fears over the severity of breakthrough infections, fails to see the bigger picture of what's driving the emergence of variants in the first place: nearly half the planet with no vaccines.

"Allowing 3.5 billion people to remain unvaccinated is a recipe for unmitigated disaster because worse and worse variants will emerge not to speak of the millions of people who will die," said Dr. Madhukar Pai,a professor of epidemiology and global health at McGill University in Montreal.

"It just completely boggles my mind why world leaders, especially those who can and could have done something, have chosen to allow this inequity to continue."

To put it in perspective, just 1.8 per cent of people in low-income countries have received at least one dose of a COVID-19 vaccine, compared to more than 50 per cent of those in wealthy countries.

Pai, who co-authored a correspondence in the journal Nature with Chagla this week on the need to vaccinate the developing world, says ramping up efforts to vaccinate the world to prevent the emergence of new variants altogether should be a global priority.

"We're now in a fourth wave because of delta. There is no way to prevent worse variants from not only emerging, but also coming into our countries," he said. He wants to see wealthy nations immediately band together, donate vaccines and fund global manufacturing.

"Because if we don't do it, we are in this forever."