Neglect herd immunity. Why COVID vaccines are nonetheless our greatest hope

Protection from an infection declines with every new variant, making herd immunity unattainable, however they’re nonetheless protecting individuals alive and out of hospitals

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It annoys Rodney Russell when people say the COVID vaccines are failing. If that were true, “we would be in a much worse place that would look nothing at all like ‘normal.’”

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Still, with a sixth COVID wave now officially washing over parts of Canada, with reports of people being reinfected with COVID only months after their first go around and jumbled messaging around boosters, some are wondering why vaccines aren’t doing more to put the pandemic behind us.

The virologist/immunologist in Russell wants the perfect vaccine, one that “completely shuts the door,” a vaccine better able to block infections altogether and able to handle a range of variants. Because it’s entirely reasonable to assume the virus will keep evolving to skirt immunity acquired from vaccinations and infections.

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Despite early obsessions with herd immunity, classical herd immunity leading to disease eradication or elimination is almost certainly “an unattainable goal” with COVID, Dr. Anthony Fauci and other top U.S public health officials wrote in a recent article. SARS-CoV-2 mutates constantly, “neither infection nor vaccination appears to induce prolonged protection” in many or most people, they said, and there’s been strong resistance to masking and other efforts to control its spread.

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Still, two years of circulating virus and more than a year of vaccines means a lot of background population immunity. Add in antivirals and widely available rapid tests, and while COVID is almost certainly going to be around for the foreseeable future, its control “is already within our grasp.”

If a vaccine keeps people alive, it’s good enough for us

U.S. officials have begun laying the groundwork for deciding which strain, or strains to target with new vaccines ahead of an anticipated fall and winter surge. An independent committee of Food and Drug Administration advisers last week discussed how it’s impractical to just keep adding boosters every few months. While the mRNA vaccines are a “godsend,” as one panelist described them, all are based on the original strain that emerged in 2019.

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“There was confusion at first as to whether the vaccines actually prevented infections or ‘just’ decreased disease severity,” said Russell, editor-in-chief of the journal, Viral Immunology. While protection from infection was later estimated to be as high as 50 per cent with the original Wuhan strain, “as variants emerged, the ability to block actual infection transmission seemed to go down, fast.”

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That said, Russell remembers one of his earliest discussions about the vaccines with a public health scientist. Why push out vaccines that weren’t better at blocking transmission? “His response was, ‘Public health wants to save lives. If a vaccine keeps people alive, it’s good enough for us.’”

While the window of protection from actual infection seems to shorten with each new SARS-CoV-2 variant, “the vaccines are great at keeping most people from getting really sick when they do get infected,” said Russell, professor of virology and immunology at Memorial University of Newfoundland.

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Public Health Agency of Canada data show that, from Feb. 21 to March 20, compared to people with two doses of vaccine, unvaccinated COVID cases were four times more likely to be hospitalized, and five times more likely to die. Compared to the boosted, the unvaccinated were nine times more likely to be hospitalized and 16 times more likely to die during the same month-long period.

However, re-infections are rising and there are stories of double and triple vaccinated people with breakthrough infections who didn’t land in hospital but were sick enough that they were unable to work. “The problem we face has shifted from mass mortality to a question of how to keep essential services and workplaces running,” Dr. Devri Sridhar, chair of global public health at the University of Edinburgh wrote in The Guardian.

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Immune evasion is driving re-infections, which Ontario defines as testing positive for SARS-CoV-2 again at least 90 days after a previously confirmed infection. The virus’s goal is to pick up mutations that make it more elusive and better able to dodge immunity from vaccines or old infections so that it can continue spreading. “Some viruses are exceedingly good at mutating, to the point that maintaining a strong immune response becomes difficult,” said Dr. Samira Jeimy, an immunology and allergy expert at Western University.

Super-transmissible Omicron didn’t emerge directly from Delta. “It kind of came out of nowhere” and from an earlier ancestor, said Simon Fraser University COVID modeller Caroline Colijn. The next variant of concern could come directly descended from Omicron. Or it could be a mixture of two like the “Deltacron” Delta-Omicron hybrid. All eyes now are on XE, a combination of Omicron siblings BA.1 and BA.2 that appears to be slightly faster at spreading than BA.2, though so far it doesn’t seem to be more pathogenic, more capable of causing severe disease. A new variant could also come directly from Delta, which is still out there. Delta is more lethal than Omicron, “so we could end up with a more pathogenic fast spreader,” Russell said.

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It’s possible to be reinfected with different subtypes of Omicron. A recent study from Denmark, a highly vaxxed population, found 47 cases where a person first became infected by BA.1 and then by BA.2. The majority were young and unvaccinated, most experienced mild symptoms and none were admitted to hospital.

Ontario has recorded 11,730 reinfection cases of COVID-19 from Nov. 1, 2020 up to Apr. 2, 2022. In the week ending Apr. 2, 478 were reported, up from 343 the previous week. Nearly half (47 per cent) involved 20-39-year-olds; a third involved the 40 to 59 age group. It’s hard to predict severity, Jeimy says. “Some people have had worse courses, some milder.”

While the window of protection from actual infection seems to shorten with each new SARS-CoV-2 variant, “the vaccines are great at keeping most people from getting really sick when they do get infected.”
While the window of protection from actual infection seems to shorten with each new SARS-CoV-2 variant, “the vaccines are great at keeping most people from getting really sick when they do get infected.” Photo by Javier Torres/AFP via Getty Images

Reinfections were inevitable, Russell said. In the Danish study, some were reinfected in as little as 20 days. How concerned should people be? “Not a lot,” Queen’s University infectious diseases expert Dr. Gerald Evans wrote in an email. “They are still quite uncommon in the grand scheme of things. They will happen much like we see with human coronaviruses, but not likely to be a major problem.”

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Russell agrees they won’t be a major problem, not because they’ll be uncommon (he thinks they will be more common) “but because every time we get infected we build more and broad immune memory.”

Boosting with the same mRNA vaccines is clearly reducing the odds of ending up in hospital, but additional shots seem less and less effective at preventing infection with each new variant. That’s a problem because the way out of the pandemic is to staunch transmission. “Once you get a disease under control there will be lower viral spread, and I think we’ll find there will be less infections,” said University of Toronto immunologist Tania Watts.

Pfizer and Moderna are both testing vaccines against Omicron. Others are working on vaccines against multiple strains. Canada is monitoring the emergence of variants, globally, “so we will see as soon as possible what might be headed our way,” Russell said. But we also need to be monitoring reinfections, and, even more importantly, he said, breakthrough cases making people moderately or severely sick, which would indicate the vaccines are no longer doing what they are good at and need to be swapped out.

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