A man wears a mask, as most people around him did, while the Toronto Raptors play in Toronto on March 24. Government-led public health measures, such as vaccine passports and mask mandates, are being repealed across the country, and the public is being informed about personal risk assessment and management. Nathan Denette / The Canadian Press
People who have not been vaccinated against COVID-19 contribute disproportionately to the risk of infection among those who have been vaccinated, according to a new study published as Canadians go through a pandemic phase with few remaining public health measures.
The authors of a modeling study published Monday in the Canadian Medical Association Journal say the increased risk undermines some assertion that vaccine choice is best left to individuals and supports “strong public action to increase vaccination.” the use of vaccines and restricting access to public spaces for unvaccinated people, as the risk cannot be considered “appropriate”. ”
While most governments have reduced the collection and reporting of COVID-19 data, available indicators – including wastewater monitoring – show transmission levels in Canada higher than at any other point in the pandemic before last year’s Omicron BA.1 wave. winter. Hospitalizations are also increasing, with more people being hospitalized now than ever before winter.
Meanwhile, government-led public health measures, such as vaccine passports and a mask mandate, are being lifted across the country, telling the public to assess and manage personal risk.
The trio of researchers from the University of Toronto’s School of Public Health in Dala Lana created a model of respiratory viral disease, presenting people as either susceptible to infection, infected and contagious, or recovered from an immune infection. These wards were then divided into two subpopulations, with 80% of people vaccinated and 20% not vaccinated.
They then simulated scenarios to accept different amounts of mixing, taking into account the human tendency to interact with people like themselves. They also adjusted the values to capture the different dynamics of the Delta and Omicron variants, the latter of which was just emerging at the time.
Lead author David Fissman, an epidemiologist and professor at DLSPH, said the group has found that vaccination status and the way these groups mix interact in important ways.
“Especially when you have a lot of mixing between vaccinated and unvaccinated people, unvaccinated people actually get protection from vaccinated people who act as a buffer – but that comes at a cost to the vaccinated,” said Dr Fisman, who co-authored the study with PhD student Afia Amoako and epidemiologist in infectious diseases and mathematical modeling Ashley Tweet.
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As the groups became more divided, the final size of the epidemic decreased among the vaccinated group, but increased in the unvaccinated group due to the loss of buffering through interaction with vaccinated people, the researchers found.
“The only counter-intuitive finding is that even when the risk of vaccination decreases, the relative contribution of unvaccinated people to vaccine risk actually increases,” said Dr. Fisman.
When the groups are largely divided, lower immunity among the unvaccinated group increases the number of cases directly caused by an infected individual – a measure called the reproductive number. As this group experiences a “roaring epidemic,” the little contact they have with vaccinated people increases the risk disproportionately, Dr. Fissman explained.
“It’s rising more and more the more you disperse the groups without completely separating them,” he said.
Researchers note that there is enough precedent to regulate public health, which protects the wider community from the spread of communicable diseases, even if that protection comes at the cost of individual freedom. A person who refuses treatment for tuberculosis, for example, can be legally detained in a hospital to protect society.
“We also note that the use of legal and regulatory instruments to prevent behaviors and practices that pose a risk to the general public also extends beyond communicable infectious diseases, such as laws restricting indoor cigarette smoking,” the authors write.
Vardit Rawicki, a professor of bioethics at the University of Montreal and Harvard Medical School, said the study added additional support to the rationale behind many of the public health measures that were in place, such as discretionary vaccine passports.
The ethics of the various measures, she said, include an analysis of the weight and benefits of carrots against a stick and depends on the current situation: How much virus is circulating in the community? How much risk does this pose to society? Is the health system able to respond enough? What is the price of individual freedoms?
In some scenarios, it may no longer be ethically justified to impose certain measures if they are exceeded by the cost of individual freedoms, said Dr. Rawicki, who is also president of the International Bioethics Association.
“But there is a third dimension to the balance, and that is that the more you give back the weight of those of us who are young and capable and can handle the infection well and get vaccinated, the more we create a society, the more dangerous it is for us.” the vulnerable, the elderly, those with comorbidities, the immunocompromised, those who cannot be vaccinated for medical reasons, young children, ”she said.
“We are turning the dial again to increase the freedom of the majority, but we are increasing the burden, risk and concerns for the vulnerable, who are a minority. And this is a value-based decision that we make as a society.
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