The from Canada鈥檚 National Advisory Committee on Immunization (NACI) strongly advise the country鈥檚 oldest residents to get their second booster shot if they haven鈥檛 done so already.
But as the highly transmissible Omicron BA.2 sub-variant continues to fuel the current wave of cases reported in Canada, members of this who recently became infected may be left wondering how long to wait before getting their fourth jab.
鈥淚n general, it's always a good idea, for almost all our vaccines, to wait about three months after an infection before getting vaccinated,鈥 Dr. Dawn Bowdish told CTVNews.ca in a phone interview on April 20. Bowdish is an associate professor at McMaster University in Hamilton, Ont., and a Canada Research Chair in aging and immunity.
According to guidance published by the (PHAC) in early February, those infected with SARS-CoV-2 after their primary series 鈥 which refers to their first two vaccine doses 鈥 but before their third dose, should wait at least three months to get a booster shot. This applies to all Canadians aged 12 and older.
The three-month time period begins with the onset of COVID-19 symptoms, or a positive test if someone is asymptomatic. This is considering a person has already waited at least six months since their most recent vaccine dose. No explicit guidelines are provided by PHAC on how long an infected person should wait before getting their fourth dose, however.
Getting vaccinated too soon after a COVID-19 infection won鈥檛 offer an ideal amount of protection against future infections or severe outcomes, Bowdish said. After a person is infected with COVID-19, antibodies will continue circulating in their bloodstream for a period of time, explained Dr. Christopher Labos, a cardiologist and epidemiologist based in Montreal. These antibodies were produced in response to the virus. If a person were to get vaccinated while these antibody levels remain high, their body wouldn鈥檛 generate any new antibodies from the vaccine, he said.
鈥淚f you get your booster shots too soon after you've been infected, they won't actually do anything,鈥 he told CTVNews.ca on April 20 over the phone. 鈥淪o you want to wait long enough for the antibody levels to start to fall so that your booster shot actually does something, which is stimulate your immune system to keep making antibodies.鈥
Waiting at least three months after contracting COVID-19 can improve the efficacy of the vaccine by allowing any existing antibodies created as a result of the infection to clear out first so that the vaccine has no interference to mounting a new immune response, Bowdish said.
Waiting a few months also provides the body with time to recover from the infection, Labos said. In general, people should not be getting vaccinated during an active infection, he said, whether it was caused by COVID-19 or another illness.
鈥淣umber one, you might infect the people at the vaccine centre,鈥 Labos said. 鈥淎nd two, it's going to be very hard for you to tease out the differences between the vaccine side-effects and the symptoms of your illness.
鈥淵ou generally want to be in good health when you get vaccinated.鈥
FINDING THE 鈥楽WEET SPOT鈥 BETWEEN VACCINES
While it may be important to give the body some time to recover from infection before getting another dose of a COVID-19 vaccine, Bowdish also cautions against waiting too long to get boosted. Several studies conducted since Omicron first appeared in November 2021 have shown a considerable waning in protection offered from vaccines about three to four months following a third dose.
According to a , the efficacy of three Pfizer vaccine doses against symptomatic disease brought about by Omicron was 67.2 per cent after two to four weeks. However, at 10 weeks post-vaccination, three doses of the vaccine were only 45.7 per cent effective against symptomatic COVID-19 illness. published by the U.S. Centers for Disease Control and Prevention earlier this year revealed that vaccine effectiveness against hospitalization fell from 91 per cent at two months after receiving a third dose, to 78 per cent at four months after.
鈥淭he data is pretty clear that the farther out from whatever your last dose was ... the more chances you have of getting infected,鈥 Bowdish said. 鈥淸After] you get your dose, then you've got a good three months where you can reasonably expect to be very highly protected, both from serious infections and also from symptomatic infections.鈥
This waning effectiveness of vaccines is even more pronounced in the elderly, Labos said. As people get older, they don鈥檛 generate a particularly robust immune response following exposure to COVID-19 infection or vaccines, meaning any immunity that鈥檚 generated as a result tends to wane more quickly, he said. Therefore, protection from fourth doses would provide them with a greater benefit compared to those who are younger and healthier, said Dr. David Carr, an emergency physician at the University Health Network in Toronto.
鈥淲e know that the most important risk factor for severity of illness is age,鈥 Carr told CTVNews.ca in a phone interview on April 20. 鈥淲hen you look at the people who are the most vulnerable, who need to be the most careful, who are going to be the last ones to take off their masks and the first ones to get their vaccines, it only makes sense that we prioritize the elderly.鈥
In terms of finding the 鈥渟weet spot鈥 for COVID-19 fourth doses after infection, Labos would recommend waiting between three and six months. However, those who are older in age should aim to be vaccinated on the shorter end of that window, closer to three months rather than six months, he said. This is provided the person has already waited the appropriate amount of time after their most recent vaccine dose. Based on NACI guidance, Canadians are advised to get their fourth dose of the vaccine at least six months after their third dose.
鈥淵ou have to weigh the fact that the longer you wait, the more benefit you can derive from the booster, but the longer you wait, the more your previous immunity might wane,鈥 he said. 鈥淪o striking that balance is a little bit complicated.鈥
Currently in Canada, about 54.3 per cent of are vaccinated with their primary series and a booster dose. Many jurisdictions in Canada have already made fourth doses available to Canadians younger than 80 years of age.
IMPLICATIONS OF HYBRID IMMUNITY
Those who have already received three doses of the COVID-19 vaccine and have also been infected with the virus possess a form of hybrid immunity, which Bowdish described as 鈥渢he best of both worlds,鈥 as both factors are contributing to a longer-lasting immune response against COVID-19.
鈥淗ybrid immunity does create a significant advantage,鈥 Carr said. 鈥淚t means your body's reacted to two different types of exposures, a full exposure and a partial [exposure], and there are gains from that.鈥
As a result, Labos said it鈥檚 possible that these people may have a sufficient amount of protection for the time being, meaning a fourth dose may not be necessary for several months.
鈥淚t is conceivable that with three doses, you'll have good immunity, six to nine months out,鈥 Labos said. 鈥淭hat is not outside the realm of possibility.鈥
However, this immunity varies from person to person, Bowdish said, and data stemming from studies that explore hybrid immunity are limited. These are some of the reasons why it鈥檚 still advised that Canadians get their recommended vaccine doses, regardless of whether they鈥檝e already been infected with the virus, she said.
鈥淪ome people have excellent hybrid immunity that we expect would protect them, and some people do not,鈥 she said. 鈥淭hat heterogeneity makes it really hard to make recommendations, so we tend to always err on the side of protecting the most people possible, which is recommending everyone get all their doses.鈥
Ultimately, Carr encourages Canadians to consider their individual risk factors when determining when and whether to get their second booster shot, if they are eligible. Despite general recommendations on fourth doses, there鈥檚 no 鈥渙ne-size-fits-all approach,鈥 Carr said.
鈥淓veryone has different health conditions and risks and anxieties and risk tolerance,鈥 said Carr. 鈥淚t's not a simple answer.鈥
For those who are considered high-risk and primed for their fourth dose, meaning it鈥檚 been at least three months after their infection and six months since their last vaccine dose, Labos would advise getting a fourth shot.
鈥淚f you鈥檙e somebody who is eligible for a fourth [dose], I would get it because it is going to give you that extra degree of protection in a setting where there's a lot of community spread of COVID and there's very few restrictions in place for limiting its spread,鈥 he said.
For those who are currently infected but have already had three doses of a COVID-19 vaccine, Labos suggests waiting at least three months and reassessing personal risk to determine whether or not they should get vaccinated with a fourth dose then, or put it off until the fall. By then, experts will be able to assess whether new variants have emerged and if that may offer better immunity, Labos said. It will also allow for more time to observe what the long-term immunity of third and fourth doses of the COVID-19 vaccine looks like at a population level.
Carr also recommends that people speak with their family doctors about personal risk factors and ways to mitigate their chances of contracting COVID-19, he said. This includes past medical history, previous COVID-19 infections, and aspects of their lifestyle that could place them at higher risk of infection.
鈥淭hey have to look at their continued exposure [to COVID-19], risk tolerance and their individual health to make those decisions, [which] they can offload with their practitioners,鈥 Carr said.
With files from The Canadian Press and CTV's Heather Butts.
-------
With the emergence of a new COVID-19 variant of concern, labelled Omicron, CTVNews.ca wants to hear from Canadians with any questions.
Tell us what you鈥檇 like to know when it comes to the Omicron COVID-19 variant.
To submit your question, email us at dotcom@bellmedia.ca with your name, location and question. Your comments may be used in a CTVNews.ca story.
Donald Trump has said he wouldn't be a dictator 鈥 'except for Day 1.' According to his own statements, he's got a lot to do on that first day in the White House.
Applause erupted over and over at the Canada Life Centre in Winnipeg Sunday as the son of Murray Sinclair, a former judge, senator and chair of the Truth and Reconciliation Commission into residential schools, spoke about his father.
A children's book written by British celebrity chef Jamie Oliver has been withdrawn from sale after it was criticized for causing offense to Indigenous Australians.
The union representing some 1,200 dockworkers at the Port of Montreal has overwhelmingly rejected a deal with their employers association.
A man who was critically injured in a police-involved shooting in Hamilton late Sunday afternoon has died in hospital, says the province鈥檚 police watchdog.
Prime Minister Justin Trudeau announced voters in Cloverdale鈥擫angley City will pick their next member of Parliament on Dec. 16.
Donald Trump's Mar-a-Lago club has been brimming in the last 48 hours with two kinds of people: those angling for a job in the president-elect鈥檚 incoming administration, and those trying to influence him into hiring their picks for the top spots.
Tenty-five of the 43 monkeys bred for medical research that escaped a compound in South Carolina have been recovered, officials said Sunday.
A government-funded report released to 麻豆影视 highlights 'systemic racism' against dozens of Black executives within the federal public service, including allegations of abuse, violence and harassment that, in some instances, led to suicide.
The union representing some 1,200 dockworkers at the Port of Montreal has overwhelmingly rejected a deal with their employers association.
A government-funded report released to 麻豆影视 highlights 'systemic racism' against dozens of Black executives within the federal public service, including allegations of abuse, violence and harassment that, in some instances, led to suicide.
A man who was critically injured in a police-involved shooting in Hamilton late Sunday afternoon has died in hospital, says the province鈥檚 police watchdog.
Police in Newfoundland say a man was electrocuted Saturday by a downed power wire about 10 kilometres north of St. John's, N.L.
Applause erupted over and over at the Canada Life Centre in Winnipeg Sunday as the son of Murray Sinclair, a former judge, senator and chair of the Truth and Reconciliation Commission into residential schools, spoke about his father.
Nova Scotia's New Democratic Party says a candidate criticized by the Centre for Israel and Jewish Affairs for "troubling" and "damaging" social media posts is no longer running for the party in the Nov. 26 general election.
Donald Trump's Mar-a-Lago club has been brimming in the last 48 hours with two kinds of people: those angling for a job in the president-elect鈥檚 incoming administration, and those trying to influence him into hiring their picks for the top spots.
Much of the U.S. federal workforce is on edge and bracing itself for the likelihood its ranks will be purged when President-elect Donald Trump takes office.
Donald Trump has said he wouldn't be a dictator 鈥 'except for Day 1.' According to his own statements, he's got a lot to do on that first day in the White House.
Thousands of Spaniards marched in the eastern city of Valencia on Saturday to demand the resignation of the regional president in charge of the emergency response to last week's catastrophic floods that left more than 200 dead and others missing.
Paris police said Sunday that 4,000 officers and 1,600 stadium staff will be deployed for a France-Israel soccer match to ensure security in and around the stadium and on public transportation a week after violence against Israeli fans in Amsterdam.
Gunmen open fired in a bar in central Mexico killing 10 people and injuring seven, a local official said.
Murray Sinclair鈥檚 family members say the late justice and senator has been laid to rest according to his wishes.
Prime Minister Justin Trudeau announced voters in Cloverdale鈥擫angley City will pick their next member of Parliament on Dec. 16.
Canada's ambassador to the United States 鈥 and co-lead of the federal government's Team Canada war room 鈥 says U.S. president-elect Donald Trump has a different understanding of the bilateral relationship than he did during his first term in the White House.
Just five more minutes of exercise doesn鈥檛 sound so bad, right? Especially when such a small amount may improve your blood pressure, according to a new study.
Researchers say taking a peek inside a person's brain is as difficult as understanding the universe or discovering the ocean in its entirety.
B.C. health officials say they have detected Canada's first-ever case of H5 avian influenza in a human.
Bernadett 'Bett'鈥 Szab贸, a 19-year-old Hungarian sex worker, was murdered in the Dutch capital in 2009. Now, more than 15 years after her death, police are hoping to uncover new information about her killing.
In 1916, Harold Wrong plucked a flower from the fields of Somme, France and tucked it into a letter he mailed home to Toronto. For decades, the type of flower sent remained a mystery.
Elwood Edwards, who voiced America Online鈥檚 ever-present 'You鈥檝e got mail' greeting, has died Tuesday at his home in New Bern, N. C. He was 74.
Taylor Swift came out on top at the 2024 MTV EMAs on Sunday, walking away with best artist, best U.S. act, best live act and best video for 鈥淔ortnight鈥 (featuring Post Malone).
Chu shared on his Instagram Stories that he and his wife Kristin Hodge welcomed their fifth child on Saturday, writing that he 鈥渃an鈥檛 believe this happened while the movie is premiering.鈥
On Thursday morning, Dave Penny officially ended a suggested hundred-day isolation period that followed his diagnosis and stem cell treatment for non-Hodgkin's Lymphoma. On Thursday night, Penny returned to a stage at a downtown St. John's bar, regaling a small crowd with songs and stories with a distinctive Newfoundland flair.
Shannon Davidson was let go from her executive role at a marketing firm last year after a merger led to cuts. She knew she wasn't done with her career yet, but finding her next workplace in her mid-50s was a daunting prospect.
Bitcoin on Sunday hit a new record above US$80,000. The world鈥檚 largest cryptocurrency surged in the run-up to Tuesday鈥檚 US presidential election, rose sharply immediately on election night after it became clear Donald Trump would win and has continued rising in the days since his victory.
Contract negotiations resume today in Vancouver in a labour dispute that has paralyzed container cargo shipping at British Columbia's ports since Monday.
Doom spending, or the practice of spending money to soothe fears about broader issues like politics or the economy, shows up everywhere from YouTube and TikTok videos to Reddit to personal finance discussions and data in surveys.
A Vancouver designer is making waves in the architectural world with an outdoor modular building created to address the city鈥檚 unrelenting housing crisis.
A rare letter signed by three of the U.S. Founding Fathers of the United States is going on sale, and is expected to fetch up to US$1 million when it goes under the hammer next week.\
The Edmonton Oilers may have found the break they were looking for.
No. 15 LSU has been criticized for unveiling a live caged tiger in its stadium for the first time in almost a decade before they were routed 42-13 by No. 11 Alabama in their SEC showdown.
A Maui man who lost a part of his leg to a shark bite is now out of the hospital and thanking those who saved his life and helped him recover.
Select Porsche owners in Canada have been told to stop driving their cars immediately and to seek repairs after an issue was identified that could cause wheels to separate from vehicles.
A driver's trip from London, Ont. to Ottawa to visit their girlfriend ended in a traffic stop for speeding on Highway 417, according to police.
Recall notices have been issued for some Volkswagen models from 2006 to 2019 for airbag safety issues.
A congestion crisis, a traffic nightmare, or unrelenting gridlock -- whatever you call it, most agree that Toronto has a congestion problem. To alleviate some of the gridlock, the Ontario government has announced it plans to remove bike lanes from three major roadways.
For the second year in a row, the 鈥楪ift-a-Family鈥 campaign is hoping to make the holidays happier for children and families in need throughout Barrie.
Some of the most prolific photographers behind CTV Skywatch Pics of the Day use the medium for fun, therapy, and connection.
A young family from Codroy Valley, N.L., is happy to be on land and resting with their newborn daughter, Miley, after an overwhelming, yet exciting experience at sea.
As Connor Nijsse prepared to remove some old drywall during his garage renovation, he feared the worst.
A group of women in Chester, N.S., has been busy on the weekends making quilts 鈥 not for themselves, but for those in need.
A Vancouver artist whose streetside singing led to a chance encounter with one of the world's biggest musicians is encouraging aspiring performers to try their hand at busking.
Ten-thousand hand-knit poppies were taken from the Sanctuary Arts Centre and displayed on the fence surrounding the Dartmouth Cenotaph on Monday.
A Vancouver man is saying goodbye to his nine-to-five and embarking on a road trip from the Canadian Arctic to Antarctica.
Weather watchers were treated to an exceptionally rare display on Friday evening as rare cloud formations filled Vancouver skies.
For some shoppers it was Nov. 1, but for others the first hints of Christmas - saccharine treats, festive-fragranced candles and gaudily wrapped gift sets - were being noticed in stores long before the final Halloween decor had been cleared.
Thousands of people are expected to gather in downtown Vancouver on Monday to observe the city鈥檚 100th Remembrance Day ceremony.
A man who was critically injured in a police-involved shooting in Hamilton late Sunday afternoon has died in hospital, says the province鈥檚 police watchdog.
A man is wanted after allegedly presenting himself as a rideshare driver then sexually assaulting a woman from Brampton late last week, say police.
Patrons were inside a movie theatre when a suspect fired bullets at the business鈥 doors on Saturday night, before the cinema was shot at again hours later in a second incident, police say.
A pair of 105-mm howitzers bark constantly as they turn plywood tank targets into kindling kilometres away on the windswept landscape of one of Canada's largest military bases.
Two semis were among the vehicles involved in a multi-vehicle crash that brought westbound traffic along Stoney Trail Northwest to a standstill on Sunday.
More than 700 people danced, ate, and sang to celebrate Diwali Saturday night at the Genesis Centre in northeast Calgary.
An Ottawa boy with a rare disease will be getting the chance to see Taylor Swift in concert after the winner and organizers of an auction held on his behalf gifted the tickets to him.
CTVNewsOttawa.ca looks at Remembrance Day ceremonies in Ottawa.
After months of controversy surrounding a dog park in Ottawa's west end, a solution has been reached to divide the park in half.
The union representing some 1,200 dockworkers at the Port of Montreal has overwhelmingly rejected a deal with their employers association.
Despite some opposition, a motion was passed at the party鈥檚 convention in Levis, Que. over the weekend to create a Quebec constitution.
The West Island Mission hosted its second food drive Sunday amid increasing demand.
Monday is Remembrance Day, a time to honour armed forces members who have died in the line of duty.
Boasting 2,300 square metres of skating space at its new location, Edmonton's Rollers Roller Rink believes it is the largest in Canada.
A woman is dead after a driver crashed a truck through a Boston Pizza in Fort McMurray late Saturday morning.
Here鈥檚 what鈥檚 opened and closed across the Maritimes on Remembrance Day.
Police in Newfoundland say a man was electrocuted Saturday by a downed power wire about 10 kilometres north of St. John's, N.L.
The Royal Canadian Legion Weymouth Branch 67 Remembrance Day ceremony will display its new basement, accessible doors and other upgrades thanks to community support.
A pillar in Canada鈥檚 history was honoured in Winnipeg Sunday afternoon, with thousands showing up to pay tribute to the life and legacy of the late Murray Sinclair.
Winnipeg police have identified two men involved in a stabbing incident earlier this week.
The Winnipeg Blue Bombers whipped the Saskatchewan Roughriders 38-22 in Saturday's CFL West Division final to earn their fifth consecutive trip to the Grey Cup.
Regina author Valerie Crowther is celebrating the release of her book 鈥榃ar Letters: Linking Lives in the Second World War.鈥
It was a somber day at Mosaic Stadium as members of the Saskatchewan Roughriders officially cleaned out their stalls and closed the book on the 2024 season.
Twilight Tech Arcade, an entertainment location specializing in retro gaming, is closing its doors for the foreseeable future.
A man has been charged after a stabbing at an apartment building in Kitchener.
The Guelph Police Service is putting out a warning after two deaths in the downtown area.
Two new tributes to Canada鈥檚 veterans have been unveiled at the Elmira Cenotaph.
Saskatchewan RCMP are searching for a suspect after a man was seriously injured in a farm-related incident in Montreal Lake.
It was a somber day at Mosaic Stadium as members of the Saskatchewan Roughriders officially cleaned out their stalls and closed the book on the 2024 season.
The Regina Rams claimed the Hardy Cup after a hard fought battle against the Saskatoon Huskies 19-14 on Saturday in the first all Saskatchewan U-Sports western conference final since 2002.
CTVNewsNorthernOntario.ca is livestreaming the annual Remembrance Day ceremony at the Sudbury Community Arena starting Monday at 10:30 a.m.
Donald Trump has said he wouldn't be a dictator 鈥 'except for Day 1.' According to his own statements, he's got a lot to do on that first day in the White House.
Police have arrested a 15-year-old in connection with a break-in and $50,000 in damage done to the Centennial Arena in Elliot Lake in September.
The events will start at 10:15 a.m. with a parade that forms up in front of the Delta London Armories, marches east on Dundas Street and turns north onto Waterloo Street to Dufferin Avenue, the west to the Cenotaph.
Emergency crews responded to the scene on Road 68/Highway 2 east of Thamesford around 7 p.m.
On Friday, the Sarnia Police Service (SPS) received a report of an alleged abduction in the area of Kathleen Avenue and Walnut Avenue.
A group of former NHL players faced off against York Regional Police officers in Newmarket Sunday afternoon to raise funds for Special Olympics programs across the province.
A driver is facing multiple charges after a multi-vehicle collision on Highway 400 early Sunday morning.
The agreed statement of facts was read to the court on Friday in the case of Alex Williams, the 24-year-old jail guard charged last fall with smuggling cannabis and tobacco into Central North Correctional Centre in Penetanguishene.
For Gene Lotz, the spark of curiosity to delve into the history of those who served in war only began when the answers became difficult to find.
One person has been arrested after Chatham-Kent Police Service (CKPS) received multiple complaints about an alleged drunk driver.
An individual is dead following a collision involving a motorcycle in Kingsville.
Environment Canada says heavy rain and winds could cause power outages on Vancouver Island as an "intense" storm system is set to hit the B.C. coast Sunday.
Six deer were struck by vehicles in six different locations in a six-hour period on B.C. highways on Saturday, according to the transportation ministry.
The union for locked-out port workers in British Columbia says the BC Maritime Employers Association cut off talks in less than an hour Saturday, refusing to budge on a final offer that the union has so far rejected.
The emergency department at South Okanagan General Hospital in Oliver, B.C., will be closed for 31 hours this weekend, the second such closure in a week and the third since the start of November.
Police in Kamloops, B.C., are reminding parents and guardians to check their children's Halloween candy after receiving a report of a mother finding a razor blade in one of her daughter's treats.
More than two years after Alannah Brown and Douglas Barker were found dead north of Penticton, police are asking for help identifying a vehicle they believe was associated with the crime.
The Southern Alberta Recreation Association is officially announcing the Town of Taber as next year鈥檚 host for the Southern Alberta Summer Games.
The Lethbridge Hurricanes broke open a close game with three goals in the first two minutes of the third period as they defeated the Warriors 7-3 in a game played Friday night in Moose Jaw.
There might not a lot snow just yet, but many southern Albertans are still itching to get outdoors.
Police have arrested a 15-year-old in connection with a break-in and $50,000 in damage done to the Centennial Arena in Elliot Lake in September.
Mayors of the five largest cities in northern Ontario met in North Bay the last two days to discuss a range of critical issues impacting their cities and the region.
Residents in the Sault expressed concerns ranging from vandalism to privacy invasions during recent consultations on the city's plan to install automated speed enforcement cameras.
Police in Newfoundland say a man was electrocuted Saturday by a downed power wire about 10 kilometres north of St. John's, N.L.
On Thursday morning, Dave Penny officially ended a suggested hundred-day isolation period that followed his diagnosis and stem cell treatment for non-Hodgkin's Lymphoma. On Thursday night, Penny returned to a stage at a downtown St. John's bar, regaling a small crowd with songs and stories with a distinctive Newfoundland flair.
A Memorial University scientist says the mysterious white blobs washing up on Newfoundland beaches are actually gobs of plastic -- and they need to be cleaned up.
The Shopping Trends team is independent of the journalists at 麻豆影视. We may earn a commission when you use our links to shop.聽Read about us.
