COVID-19 breakthrough cases signal next phase of Canada’s battle


There are signs that some parts of the world are already encountering problems with weakening immunity from vaccination.


[Excerpts] To find out how vaccines are holding up in the running battle against COVID-19, Anne-Claude Gingras is being guided by the lights.

In her lab at Mount Sinai Hospital in Toronto, Dr. Gingras is culturing cells that have been engineered to glow when they are infected with the coronavirus. The approach is a standard laboratory technique that can be used to see if antibodies from vaccinated individuals can block infection. Dr. Gingras is using it to study how that blocking ability is compromised by emerging COVID-19 variants.

“We can get a really good measurement of neutralization by looking at how much light production in the cells is decreased,” said Dr. Gingras, who is a senior investigator at the hospital’s Lunenfeld-Tanenbaum Research Institute.

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With this setup, Dr. Gingras and her colleagues can recreate a breakthrough infection – a situation where the coronavirus manages to defeat the antibodies that vaccination has raised against it. That scenario is top of mind for Canadian public-health officials as they grapple with the fourth wave of the pandemic, propelled by the Delta variant, which is the most contagious version of COVID-19 so far.

As of Friday, new cases are rising steadily across Canada, in the range of 3,000 per day. That is comparable to the national picture in late May. In contrast, the number of cases in hospital are just a quarter of what they were then, a sign that vaccines are preventing many cases from becoming serious. But the upward trend is still a worry, in part because fully one-third of the country remains unvaccinated, including all children under 12. That has left plenty of room for the pandemic to keep rolling with a new, more transmissible variant that seems almost impossible to dodge without the aid of a vaccine.

There are signs that some parts of the world are already encountering problems with weakening immunity from vaccination. For example, Israel, which began its vaccination campaign well ahead of other countries, is now experiencing an increasing rate of breakthrough infections. Last week, it became the first country to offer third doses to those who are 50 or older. On Wednesday, the United States said it would also begin rolling out third doses starting next month. The move toward additional protection has been hastened by the near absence of public-health measures in many states.

Canada has not yet reached the third dose threshold – with the important exception of people who are immune compromised, such as transplant patients – but it’s likely heading in that direction. According to the Public Health Agency of Canada, by the beginning of this month about 0.03 per cent of fully vaccinated Canadians had become infected with COVID-19. While the number of breakthrough infections is small, the prevalence of the Delta variant ensures that it will grow.

New data shared by Ontario’s science table puts the current situation in focus. The ratio of cases between unvaccinated and vaccinated individuals now stands at roughly 10 to 1 in Ontario. The ratios are closer 30 to 1 and 75 to 1 for COVID-19 cases currently in hospital and in intensive care units, respectively, when figures are adjusted to take into account both the lower disease risk and lower vaccination rate among younger people. Vaccinated individuals are also about 10 times less likely to get long COVID-19, when symptoms persist for months or longer, Dr. Juni said, although this estimate is based on limited studies.

Put another way, in a room full of 100 Canadians that are representative of the entire population, 35 individuals will currently be unvaccinated. Over time, nearly all of those unvaccinated people, about 33 of them, can expect to become infected as the virus circulates in the room. About six cases would be expected to arise among the fully vaccinated group. Bottom line: we can assume that only about 60 people in the room of 100 are “safe” from infection.

What this means is that while vaccines drastically improve the odds for those who take them, vaccinated people can still be infected and they can play a significant role in transmitting COVID-19 to the unvaccinated.

As a result, distancing, face masks and limiting discretionary gatherings will remain important tools for controlling the fourth wave. Such efforts will buy time until regulators give the green light for children to be vaccinated, and until more of those who are hesitant decide to take the shot. But, as time passes, more breakthrough infections can be expected.

COVID-19 breakthrough cases signal next phase of Canada’s battle