More than five million Ontarians will need a third COVID-19 vaccine by the end of December to boost their protection against Omicron, according to the scientific director of the province’s science advisory table, who warns a third-dose rollout at the scale and urgency of the summer mass clinics is needed to stay ahead of the new variant.
With millions of second doses administered during the summer, the number of adults needing a third shot to keep up immunity against the virus grows daily, prompting experts to call on the province to open up eligibility to more age groups.
On Monday, Ontarians 50 and over who received their second dose at least 168 days ago will be eligible to sign up for a third dose, meaning about 1.6 million people will become eligible on that day alone, by the Star’s count.
Emerging data on the Omicron variant indicates Ontario should expand its third-dose rollout to all adults who are six months past their second dose, a prospect that raises questions about whether the province’s capacity to vaccinate at the scale seen during the height of the summer blitz — which saw more than 200,000 shots administered on many days — is again attainable.
Swiftly moving forward with third doses will be key to mitigating an Omicron winter wave, said Dr. Peter Juni, epidemiologist and scientific director of the Ontario COVID-19 Science Advisory Table, an independent group of experts that gives the government advice on the pandemic.
“The game has changed completely, and the rules of the game have changed with it,” Juni said, referencing the arrival of the new variant of concern. “The age limits used to justify third doses … have become obsolete with Omicron.
“We need a campaign that first and foremost makes sure that people understand how needed third doses have become,” he added. “This is a three-dose vaccine we know for sure now with the threat of Omicron.”
The province was able to vaccinate more than 265,000 people in a single day at the height of this past summer’s vaccination campaign. Ontario has been administering between 60,000 and 80,000 doses in recent days. To date, the province has administered just under 915,000 third doses.
A week ago, the provincial government announced that it was accelerating its staged rollout of third doses by lowering the age eligibility to Ontarians 50 and over. Thirddose eligibility was already opened in early November to those 70 and above, health-care workers and essential caregivers in congregate settings, people who received two doses of the AstraZeneca vaccine or one dose of the Johnson & Johnson shot, as well as First Nations, Inuit and Mtis adults.
But looking solely at the Ministry of Health’s guidance that third doses be given 168 days, or about six months, after the initial series of two doses, the number of Ontarians across all age cohorts needing a booster now and in the coming months increases drastically.
Michelle Dagnino, the executive director of the Jane/Finch Community and Family Centre, said the earlier stages of the vaccine rollout have shown that neighbourhood pop-up clinics are the best way to reach a lot of people at once, especially in hard-hit areas. But they will need to be scaled up with staff and supplies to meet third-dose demand.
The messaging also needs to shift toward the urgency of third doses, she added. Right now, the focus of Jane and Finch community ambassadors, for example, is still on encouraging people to get their first dose.
Phillip Anthony, manager of the East Toronto Mobile Vaccination Strategy at Michael Garron Hospital, agrees the message will be key.
“We know that this is now a threedose vaccine series, and it’s just a matter of getting that messaging out and having people understand that,” he said.
In Denmark, where the Omicron variant has spread across the country and triggered new restrictions, data suggests that a two-dose vaccine series protects against hospitalization, but offers relatively little protection against infection, Juni said. However, data indicates a three-dose mRNA vaccine series offers “considerable protection” against infection, he said, noting this is consistent with initial laboratory reports investigating how the vaccines work on Omicron.
It’s not yet clear what the optimal interval is between the second and third vaccine dose with the emergence of Omicron, but research on the Delta variant shows immunity triggered by a dual dose of vaccines starts to wane at about six months, Juni noted.
Research on vaccine effectiveness conducted prior to Omicron by scientists at the non-profit ICES, formerly the Institute for Clinical Evaluative Sciences, in Toronto and others, suggests that protection offered by vaccination wanes against infection, but less so against the most severe outcomes of hospitalization and death.
Pre-print research that ICES conducted using databases of all Ontarians tested for and vaccinated against COVID show that mRNA vaccines remain over 90 per cent effective against hospitalization or death after six months, while effectiveness against any infection drops to the 70-80 per cent range in the same time period.
“The problem, though, is that if people who are vaccinated can still get infected, then they can spread it to others,” said Dr. Jeff Kwong, a senior scientist at ICES, and an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health. “So the more you allow it to spread, the more cases you’re going to get. And eventually you are going to get some people who get really sick.
A six-month longitudinal study published in October in the journal Science found that those who received mRNA vaccines had resilient “immune memory” against the Alpha, Beta and Delta variants of the virus. The researchers found that these memory cells could be responsible for continued protection in vaccinated individuals even if antibodies decline over time.
“Our data may also inform expectations for the immunological outcomes of booster vaccination,” the authors note.
Kwong noted that Ontario may be faring better than other jurisdictions when it comes to waning immunity due in part to the fact that the province has maintained public health measures, such as masking and, until recently, capacity limits.
Juni said Ontario should reintroduce public health measures, such as capacity limits in bars, restaurants and sporting venues, in addition to other tools, including better ventilation and stronger vaccine certificates, to help buy the province enough time to administer as many third doses as possible.
“We need to act swiftly because we see from other jurisdictions, including Denmark and the U.K., this (Omicron) goes very fast.”