The Delta variant means COVID ‘has upped its game massively.’ What Ontario can learn from the U.K. experience and new data
|Toronto Star 17 Jun 2021 at 07:16|
As COVID-19 vaccinations accelerate across the country, Canadians are inching toward a two-dose summer: patio umbrellas are reopening, vacations are being booked, and relatives are hugging for the first time in weeks, months or more than a year.
But across the Atlantic, a cautionary tale is unfolding in the United Kingdom, where the highly transmissible Delta variant of concern is driving an uptick in cases and forcing England to delay their reopening by another month.
The U.K. experience is unnerving experts around the world, including in Ontario, where case rates have been plummeting and vaccinations increasing. On Wednesday, the province reported 384 new cases — a level last seen in September — along with a record 202,984 new daily vaccinations.
But this week also saw Delta reach a tipping point in Ontario, where it’s on the cusp of becoming the dominant strain, said Dr. Peter Juni, scientific director of the province’s COVID-19 Science Advisory Table.
The next two weeks will be crucial for determining how well Ontario fares against this formidable new foe, he said.
“The virus has upped its game massively,” Juni said. “The future is in our hands. We can still mess this up.”
On Wednesday, the Science Table estimated that Delta now makes up 50 per cent of COVID cases in Ontario, translating to 200 new cases of the variant per day, according to Juni. He said a quarter are in Waterloo, which on Wednesday reported more daily cases than any other health unit.
With Delta’s greater transmissibility — and early indications of increased hospitalization rates — COVID-19 now poses an even graver threat to unvaccinated Canadians, especially in marginalized communities where the risk of infection is higher and access to vaccines more difficult.
While Delta first emerged in India, the best data on this new variant has been coming out of the U.K., including , with more reports of cold-like symptoms — headaches, runny noses and sore throats — and fewer people experiencing a loss of taste or smell.
Here’s what the latest U.K. data is telling us about the Delta story, and what it might portend for this next chapter in Canada’s fight against COVID-19.
First, the good news. On Monday, Public Health England released new research that likely unleashed a collective sigh of relief around the globe: “Vaccines highly effective against hospitalization from Delta variant,” the health agency said in a press release .
Earlier U.K. data has shown that vaccinations are less effective against Delta when it comes to preventing symptomatic infections. This is especially true for people with just a single dose of either Pfizer or AstraZeneca, both of which are 33 per cent protective against Delta. As of June 5, only eight per cent of Canadians were fully vaccinated, according to Health Canada .
But in a new pre-print study released Monday, Public Health England scientists looked at hospitalizations, another key metric for assessing vaccine efficacy and understanding the threat that Delta poses.
The analysis, which looked at more than 14,000 patients infected by Delta, found that two doses of Pfizer were 96 per cent effective against hospitalization; for AstraZeneca, a double dose was 92 per cent effective at keeping COVID patients out of the hospital.
But even with a single dose, both vaccines had “high levels of protection against hospitalization,” the study found, with a 94 per cent vaccine efficacy for Pfizer and 71 per cent for AstraZeneca.
Taken together, these results are “phenomenal,” said Dr. Isaac Bogoch, an infectious disease specialist at University Health Network and member of Ontario’s vaccine distribution task force.
“If you can turn a potentially lethal infection into the sniffles, you’re doing something right,” he said. “The key thing here is the vaccines still work against the Delta variant.”
Canada is about a month behind the U.K. in terms of Delta’s emergence, experts say. Public Health Ontario first identified the Delta variant on April 29, but when scientists looked back in their database they discovered a sample from March 20, according to spokesperson Janet Wong.
Juni said Canada has at least two advantages over the U.K. in terms of our preparation for Delta’s onslaught. First, the U.K. had much looser restrictions in the early phases of its economic reopenings, when Delta was gaining a toehold. Second, Canada’s “workhorse” vaccines — Pfizer and Moderna — are more effective against Delta than AstraZeneca, which formed the bulk of U.K.’s early vaccination strategy.
Juni warns that people who still need first doses shouldn’t be crowded out by the stampede of people now seeking second doses. In Ontario, 13 per cent of people in their 60s remain unvaccinated, and only 47 per cent of children 12 to 17 have received a first dose. Meanwhile, several GTA hot spots, such as northwestern Toronto and parts of Brampton, have seen vaccination rates slip in recent weeks.
Ontario needs to vaccinate at least 85 per cent of eligible age groups, while taking its next steps toward reopening very carefully, Juni said. Every two weeks, more than two million doses of vaccine are going into Ontarians’ arms — but two weeks is also now the doubling time for Delta in the province, he said.
“If we stick to rolling out our vaccine program, with a heavy emphasis on the mRNA vaccine, then we will most likely not end up in the same situation as the U.K.,” Juni said. “Ten to 12 days from now, we’ll see what’s happening in Ontario and how this all plays out.”
On June 2, the U.K.’s Scientific Pandemic Influenza Group on Modelling released a consensus statement with some alarming estimates. The Delta variant, the statement said, is believed to be 40 to 60 per cent more transmissible than Alpha, or B.1.1.7 — which itself was already 50 per cent more transmissible than the original strain.
“It is a bit of a game changer,” said Andrew McArthur, an associate professor with McMaster University who runs one of Canada’s genomic surveillance labs for COVID-19 and has an advisory role with Public Health Ontario. “Delta is starting to take over where it can and I expect, now that we’re opening up more, Delta will be everywhere soon.”
Juni said that when the “wild type” coronavirus first emerged in Wuhan, the basic reproduction number, or R0, was roughly 2.5 — meaning that in an unvaccinated population with no public health interventions, every positive case led to 2.5 new infections on average.
But as the virus moved across the globe, it adapted to its new human host and “evolved into something that is much more fine-tuned for transmission.” By the time the virus reached Europe, its R0 was roughly 3; the Alpha variant that drove Ontario’s third wave had an R0 of between 4 and 5.
With Delta, the R0 is between six and seven, Juni said — every positive case can now lead to an average of six or seven new infections in an unvaccinated population.
The Delta variant has two important mutations, which likely improved its fitness in human airway cells, said Wendy Barclay, a professor with Imperial College London and lead of G2P-UK, a research consortium studying SARS-CoV-2 mutations.
Two things can happen as a result, Barclay said in a press briefing last week. The first is that the amount of virus in an infected person may be higher, meaning they are exhaling more infectious virus into the air, she said.
The second is that someone who comes into contact with this contaminated air can be more easily infected, she said. “So the infectious dose — the amount of virus that a person has to be exposed to in order to actually contract the infection — is a bit less.”
Delta’s increased transmissibility translates to a greater risk of superspreader events, Juni said, meaning it doesn’t take much for a few cases to spark larger outbreaks.
He points to Waterloo as an area where Delta has recently driven a rapid escalation in cases. On Wednesday, Waterloo reported 71 new infections — more than any other health unit in Ontario — with 37 Delta cases confirmed to date.
Nobody knows how Delta slipped into Waterloo, and it’s possible travellers from GTA hot spots spread the variant to the region, Juni said. But according to Waterloo Public Health, at least two cases in the region have been linked to a , which may have seeded Delta cases across the country.
Considering the epidemiology of the mine outbreak — where the vast majority of cases were Delta — it’s “likely that these two Waterloo cases also involve the variant and may have introduced Delta to the region,” Juni said.
Hospitalizations and deaths
In the past six weeks, COVID-19 hospitalizations in Ontario have dropped substantially from mid-April’s record-setting high of 2,360 to 438 on Wednesday.
While the decrease has offered a much-needed respite for overwhelmed hospitals forced to treat critically ill patients on medical wards , experts warn that a combination of reopening Ontario too soon along with an insufficient number of people without at least one vaccine could allow the Delta variant to increase hospitalizations and deaths.
These are still early days in Delta’s emergence, so its impact on hospitalizations and deaths remains unclear. But a Scottish study found the variant roughly doubles the risk of hospitalization compared to the B.1.1.7 variant.
The next several weeks, during which England is to remain in lockdown, will allow scientists there to gather more data and refine their predictions for risk of hospitalization and death, said Neil Ferguson, director of the MRC Centre for Global Infectious Disease Analysis at Imperial College London, during a press briefing last week.