Increasing third-dose COVID vaccine coverage more important than expanding fourth doses, infectious disease experts say

“Giving a fourth dose to a healthy younger person is safe, but the incremental benefit is relatively small."

Elizabeth Payne 4 minute read May 6, 2022

Fewer than half of Ontario residents have had third doses of COVID-19 vaccine, something recommended to boost protection against the Omicron variant, though the rate is 55 per cent among Ottawa residents. Ashley Fraser / Postmedia

Ontario public health officials should concentrate on increasing third-dose uptake rather than following Quebec’s lead and making fourth COVID-19 vaccine doses available to all adults, health experts say.

Dr. Gerald Evans, an infectious disease expert from Queen’s University, is a member of Ontario’s COVID-19 Science Advisory Table. Michael Lea / Postmedia

Dr. Gerald Evans, an infectious disease specialist from Queen’s University, who is a member of Ontario’s COVID-19 Science Advisory Table, said Quebec’s decision to expand access to fourth doses of the vaccine was informed by politics, rather than science.

Quebec officials are not recommending healthy people under 60 get fourth doses, but neither are they preventing them from doing so. Quebec officials have made it clear that those who want jabs will be able to get them, as long as they are over 18.

Like Ontario, Quebec recommends anyone over 60 and those who are vulnerable, including the immune compromised, receive fourth doses of COVID-19.

Expanding fourth-dose coverage beyond that sends a message that the Quebec government is behind vaccines, Evans noted, which is not a bad thing. “I think that is a very important message. We really have to continue to remind people that the number one strategy (against COVID-19) is vaccines.”

But, beyond the messaging, he said expanding eligibility would have minimal impact.

“Giving a fourth dose to a healthy younger person is safe, but the incremental benefit is relatively small,” he said. Evans speculated that Quebec might have extra vaccine stock that could expire if not used.

Dr. Doug Manuel, a senior scientist at the Ottawa Hospital Research Institute and professor at the University of Ottawa’s School of Epidemiology, said he was more concerned about the third-dose gap in the province, especially with the prospect of waning immunity. Manuel is also a member of Ontario’s COVID-19 Science Advisory Table.

Dr. Doug Manuel is a senior scientist at the Ottawa Hospital Research Institute and professor at the University of Ottawa’s School of Epidemiology. Tony Caldwell / Postmedia

The biggest benefit to society right now, Manuel said, would be for people who have only had two doses to get third dosed, especially if it had been a while since the last dose.

Fewer than half of Ontario residents have had third doses of COVID-19 vaccine, something recommended to boost protection against the Omicron variant.

In Ottawa, third-dose vaccination rates are slightly higher than the provincial average, with 55 per cent of Ottawa residents having received three doses.

Ottawa Public Health has made a concerted effort in recent weeks to increase the number of residents over 50 who have had at least three doses. In a statement, Ottawa Public Health said staff members had phoned or emailed more than 34,000 residents between the ages of 50 and 70 who had not yet received third doses of COVID-19 vaccines.

Public health staff assist residents in booking appointments or provide drop-in options.

OPH did not say how many of those contacts had since been vaccinated with third doses, but said community clinics were seeing good uptake for appointments and drop-ins for fourth doses, as well as first, second and third doses.

More than 51,000 fourth doses have been administered in the city. Coverage for Ottawa residents 60 and over is 21 per cent. For those 70 and over, it is 31 per cent.

Manuel said Canada’s National Advisory Committee on Immunization had provided good guidance on COVID-19 vaccinations. To date, it does not recommend fourth doses be expanded to all adults, but recommends them for those over 60 and others at high risk.

But Manuel said there would be more talk about boosters in the future, likely in the fall, when it is widely anticipated that there will be another COVID-19 wave — if not sooner.

Evans said both Moderna and Pfizer, which manufacture the mRNA COVID-19 vaccines widely used in Canada, were working on bivalent vaccines combining the original strain with the Omicron strain. They could be available as boosters in the fall, he said.

Evans said he would advise a healthy 40-year-old in Quebec who had received three doses and was doing a good job of avoiding infection to wait until fall for a fourth dose.

Meanwhile, anyone who has had just two doses, should not wait to get a third, he said.

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