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A woman receives a COVID-19 vaccine at a mass vaccination clinic held inside Scotiabank Arena in Toronto on June 27.Cole Burston/The Canadian Press

Provinces are expanding eligibility for third-dose COVID-19 booster shots, part of contingency plans designed to mitigate the damage of a possible surge in cases over the winter months.

The Globe and Mail has learned Ontario will announce Thursday that people aged 50 and older will be eligible for a third dose of COVID-19 vaccines starting in mid-December. The changes were confirmed by two medical sources with direct knowledge of discussions.

Alberta plans to open up third shots to everyone 18 and older, beginning with those aged 60 and older on Monday. Additional age groups will be added depending on demand for third doses and supply, with all adults expected to be eligible by early next year.

Deena Hinshaw, Alberta’s Chief Medical Officer of Health, said the province is starting with older people first because they remain at greatest risk of severe outcomes, even if already vaccinated. The same applies to people over 70 and those with compromised immune systems, who are already eligible.

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“Because of this, and given the fact that increased transmission risk in the winter months is lining up with some waning vaccine effectiveness against infection over time, the current evidence supports expanding booster doses to add an additional layer of protection,” Dr. Hinshaw said Wednesday.

Canada’s National Advisory Committee on Immunization is also preparing to announce new recommendations for anyone 50 and older to receive a booster shot, according to two medical sources with direct knowledge of the issue. NACI, an expert committee that provides guidance to provinces on the use of vaccines, could make the announcement as early as Friday.

The Globe and Mail is not naming the sources who confirmed the Ontario and NACI announcements as they were not authorized to speak to the media.

The changes come as Canada faces growing pressure to prevent new waves of COVID-19 from taking hold as more people gather indoors and the transmissible Delta variant continues to spread.

NACI already recommends booster shots for a range of high-risk groups, such as people 70 and older, people living in congregate settings or people with conditions that could compromise their immune system.

Current recommendations and rules state that people are eligible for booster shots at least six months after their second dose. It’s unclear if NACI guidelines would stick to that timeline or if Ontario would allow residents to get boosters before that six-month mark. Public-health and infectious-disease experts say immunity starts to wane at around that timeframe, which is why many have been urging Canada to expand booster eligibility to include more people who got their second doses within that period.

Prime Minister Justin Trudeau said Canada will have a sufficient supply of booster shots if the committee determines that they are needed for everyone eligible to get the vaccines.

“There is not an issue about quantity of vaccines – we have lots of vaccines for boosters in Canada; we’re receiving more into the New Year,” Mr. Trudeau said. “We are fine in terms of quantity – the issue is, what is the best recommendation for people to get those boosters and when?”

The arrival of Omicron has created additional pressure for governments to take immediate action to mitigate the possible effects of the variant, though scientists are still unclear as to whether it is more transmissible and if it can evade the protection from available vaccines.

While the discovery of the new variant has many health experts on edge, infectious-disease experts say the Delta variant continues to pose an immediate threat here and that Canada needs to prepare now to prevent a severe uptick in cases, hospitalizations and deaths.

Some experts predict that the wave of infections in many European countries could soon occur in Canada. Many Canadians got their vaccines a few months after people in European countries, so some experts are hopeful that expanding the eligibility for third doses could help the country prevent or mitigate the effects of a possible new wave, particularly if Omicron proves to be more transmissible than the Delta variant.

With reports from Marieke Walsh, Kristy Kirkup and James Keller

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