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The fourth doses of COVID-19 vaccines are being distributed to more Canadians eligibility is open nationwidebut research suggests there are limitations to the impact they can have on the highly contagious BA.5 Omicron subvariant that feeds Canada’s first summer wave.
After increasing pressure from healthcare staff and the general public To access additional vaccinations, some provincial governments have extended the eligibility of immunocompromised and older Canadians only to anyone over 18 years of age.
But the measure contradicts the National Immunization Advisory Committee (NACI). recent recommendations that a second boost should only be given now to those most at risk for severe COVID-19, while younger Canadians could wait until the fall.
The data show that while a third dose offers a significant increase in protection against infection, hospitalization, and death: a fourth dose only offers a marginal benefit against severe COVID-19 for most, including short-term protection against infection, even in vulnerable groups.
“This fourth dose adds a small, modest decrease to the risk of developing a serious illness,” said Angela Rasmussen, a virologist with the Organization for Vaccines and Infectious Diseases (VIDO) at the University of Saskatchewan.
“But I think it’s also limited what we can expect from him; I don’t think we can expect that wave to stop.”
BA.5 has caused an unexpected seventh wave in much of Canada, which is approaching 40 percent of cases and leads to aa significant increase in hospitalizations for COVID-19because of his ability to evade protection both by vaccination and by previous infection.
MIRAR | When is the best time to get a fourth vaccine against COVID-19?
When should you receive your fourth vaccine against COVID-19?
Dr. Zain Chagla, a specialist in infectious diseases, explains who should receive a second booster of the COVID-19 vaccine and when.
4th dose of protection against short-term infection
A recent study from Israel published in New England Journal of Medicine (NEJM) found that while protection against infection and severe COVID-19 increased after a fourth dose in those over 60, the effectiveness of the infection vaccine began to decline after a few weeks.
A second study from Israel published in British Medical Journal (BMJ) found that while people 60 and older gained additional protection against hospitalization and death in the three weeks following a fourth vaccine, protection against infection “declined rapidly.”
Healthcare workers looked specifically at another Israeli study published in NEJM who found that a fourth dose provided only a marginal difference in infection rates compared to those with a third injection, and only a slight difference in the severity of advanced symptoms.
A new Canadian study published in BMJ analyzed the effectiveness of a fourth dose to Ontario long-term care residents. He found that the blow initially improved protection against infection and severe COVID-19, but the duration of that protection “remains unknown.”
“Science around this right now has only clearly demonstrated the benefits of this fourth dose of the vaccine for groups that (NACI) has outlined,” Dr. Fahad Razak, an internist at St. John’s Hospital. Michael of Toronto and scientific director of Ontario. COVID-19 scientific advisory board, he said The current on July 7th.
“That they are older individuals and immunocompromised or high-risk individuals.”
A patient receives a dose of the Pfizer vaccine against COVID-19 in London in 2021. (Alberto Pezzali / The Associated Press)
Research suggests that while there are some people who do benefit from a fourth dose, including long-term care residents, the elderly, and other vulnerable groups, there are no data to show a clear benefit for to those under 60 years of age.
Dr. Zain Chagla, an infectious disease physician at St. Joseph’s Healthcare Hamilton and an associate professor at McMaster University said older, immunocompromised Canadians can benefit from a fourth dose, but younger groups get “a very minimal benefit.”
“I don’t think there’s a big benefit here. It certainly won’t change the dynamics of the pandemic in terms of less disease. Really, to take advantage of it, almost everyone would need to receive the fourth dose. “, he said.
“And even then, look, their immunity will decrease in six to eight weeks and you’ll see that they really won’t be protected from infection anyway and BA.4 and BA.5 will still be here. In six to eight weeks.”
Canada is still missing its third dose absorption
Although now the expansion of the fourth doses to more Canadians could have a limited impact on the trajectory of the BA.5-driven wave across much of the country, the biggest problem lies in the abysmal absorption of third doses. across the country.
Less than half of Canadians they have received a third dose, which research suggests adds important protection against severe COVID-19, a number that has remained stagnant for months amid the growing push to expand fourth doses.
“The biggest problem right now is the substantial number of Canadians who have not received a third dose,” said Dr. David Naylor, who led the federal investigation into Canada’s national response to the 2003 SARS epidemic and he now co-chairs the federal government’s COVID. -19 immunity working group.
“It’s becoming increasingly clear that the bets on the table for this vaccine are three injections, and we need to stop referring to people with two doses as fully vaccinated.”
MIRAR | Why the third and fourth injections of COVID-19 are important right now:
The third and fourth features of COVID-19 are important right now, the expert says
Infectious Disease Specialist Dr. Isaac Bogoch explains who benefits from more than a fourth dose of COVID-19, but also stresses the need for many people to simply get a third injection.
But Naylor hopes that expanding the fourth doses to more Canadians could have an impact on the spread of BA.5 across the country, even if the data does not yet show a clear benefit for younger age groups. .
“For someone younger and healthier who has three shots and has had a recent infection, I can see the logic of waiting to receive a fourth vaccine,” he said.
“There is no doubt that the marginal yields of a fourth dose are small at the individual level for this population segment, but they are at risk of reinfection and broader coverage can help curb population-level spread.”
Chagla said extending the fourth doses to younger Canadians now at odds with NACI guidelines could do more harm than good in encouraging more people to return for a third injection.
“There will be people who will say, ‘Well, I’m on dose two, they already say I need a fourth dose, what good are these vaccines if they don’t protect me from getting Omicron?'”
“With each of those doses coming out, the public image of what vaccines can do changes with them and we need a lot of people to come back for their third dose.”
Rasmussen, of the University of Saskatchewan, said his concern is that many Canadians consider reinforcements “optional” with limited benefit to immunity. He said messages around the third dose should be “hammered home” to increase absorption.
“This third dose provides a significant increase in protection against both serious illness and Omicron BA.1 infection,” he said.
“This fourth dose may be incremental, maybe just a modest benefit, but the third dose I think is very clear. At least with BA.1, it provides significant benefits.”
Vaccines updated on the horizon
Time enhancements to ensure strong immune protection against COVID-19 are increasingly critical with the emergence of the highly contagious subvariants of Omicron BA.4 and BA.5, as well as a new worrying subvariant that causes an increase in called India BA.2.75.
While Canadians opting for a fourth dose of the original strain of the vaccine can now only be protected for several weeks from infection, updated bivalent vaccines that combine the original vaccine with Omicron protection are also on the horizon. .
Modern bivalent vaccine it is one in which many are putting their hopes. But experts fear that targeting the original Omicron strain may not be enough research showing a lack of cross-protection immunity against very different variants of BA.2.12.1, BA.4 and BA.5.
“The usual argument for waiting is that we can get better vaccines in the fall. However, data on bivalent vaccines are less convincing or complete than many of us had expected,” Naylor said.
Bivalent vaccines target the ear protein of the virus. They are different from newer and more innovative platforms with new goals or delivery modes such as intranasal enhancers o coronavirus vaccines.
“It has been a cup game to guess what the virus will do next, and those receiving a fourth dose in the near future will still be eligible for any new formulation from mid-October or so.”
These new vaccine technologies may stimulate a more robust immune response, due to the fact that they stimulate another arm of the immune system or target several different coronaviruses.
“We don’t know when these paradigm-shifting vaccines will be available, but it could take some time, especially if we wait, as seems prudent, for very good data on their effectiveness and safety,” Naylor said.
“For me, this reality plus the ongoing spread of BA.5 together argue to move forward with a fourth shot even if it’s more of the same with modest marginal returns.”
MIRAR | The summer COVID-19 wave is causing concern:
The summer COVID-19 wave is causing concern
The increase in cases has led some provinces to declare a seventh wave of COVID-19, which is raising concern for many health workers.
But Chagla said Canadians need to start thinking about the protection that COVID-19 vaccines offer in a different way than they did before. There will be “limits” to what they can and cannot do …