Yes, vaccines curb COVID-19 transmission — but that’s not enough to protect those without a shot

However, this does not mean that the vaccine can fully protect the unvaccinated – billions of people in total globally – especially in regions with low vaccination rates.

“Most vaccines work very efficiently to prevent transmission from the infected person to the unvaccinated person,” said Akiko Iwasaki, professor of immunobiology at Yale University School of Medicine.

In the various countries where vaccination efforts are being implemented on a large scale, there are some other clear trends emerging: Severe cases of COVID-19 are declining With high vaccination rates; ‘Breaking infections’ among fully vaccinated individuals It is rare and usually mild; Cases of serious illness – which lead to hospitalization or death – are now It is more common in the unvaccinated population.

All of this underpins the protective power of this first crop of vaccines at a time when much of the world is reopening, including Canada.

With so many unvaccinated people around the world, and due to the transmissibility of different species like Delta, this virus continues to spread, Iwasaki said.

“The whole concept behind herd immunity is to provide that protection to unvaccinated people by having enough immunized people around,” she said.

“But I don’t think we can be complacent, because this kind of herd immunity really requires vaccinating large numbers of people within a given population. And many places haven’t achieved that yet.”

Few cases of COVID-19 between full vaccinations

In Canada, cases of COVID-19 have fallen sharply in recent months, The data shows only a small percentage of these They are among the fully vaccinated Canadians.

But with more than half of the population not fully immunized, millions are still at risk of infection.

While many experts who spoke to CBC News say that vaccinated individuals help reduce transmission to those who are not yet protected, the exact mechanism behind why COVID-19 vaccines are likely to be reduced isn’t entirely clear.

Vaccines act less as a wall or shield completely preventing the virus from entering your body, said Angela Rasmussen, a virologist with the University of Saskatchewan’s Vaccines and Infectious Diseases Organization, and more like a complex army to fight back once these invaders arrive.

For example, she said, imagine someone coughing in your face. You will inhale some virus particles whether or not you have been vaccinated. But for those who are protected by the vaccine, what happens next is what makes the difference.

Watch | Vaccination rates in the United States are slowing as the number of cases rises:

Vaccination rates for COVID-19 are starting to slow in the United States even as the number of cases has risen, mostly in areas where vaccine uptake has been low. Officials are trying to stimulate a vaccine, but say more drastic measures may be needed. 1:58

Iwasaki said the immune systems of vaccinated individuals fight off the virus faster, giving it fewer opportunities to multiply, and reducing any symptoms like coughing or sneezing that would help transmit it.

“These kinds of activities, we know, drive and expel the virus much better than if you were just breathing,” she said.

Rasmussen said that because fully vaccinated individuals are usually able to clear an infection so quickly, it is “incredibly unlikely” that they would produce enough virus to infect others.

More research is needed to measure the effect on transmission

Rasmussen said that while these are the principles behind how vaccines can prevent infection and transmission, getting data from the real world to quantify how much to reduce the spread of the virus is difficult, with more research needed as SARS-CoV-2 persists. . evolve.

The team behind one of the recent studies on vaccine protection in Israel acknowledged the challenges, saying their research has several major limitations. Individual behavior, political decisions such as lockdowns, and factors such as immunity after infection have played a role in muddying the waters — making it difficult to know how much vaccines are stopping the virus’ spread.

However, after taking all of this into account, the researchers found “observable evidence that vaccination not only protects vaccinated individuals but also provides reciprocal protection for unvaccinated individuals in the community,” according to Peer-reviewed summary note in the June issue of the scientific journal Nature.

The team analyzed vaccination records and test results collected during the rapid vaccine rollout in 177 communities, and found that vaccination rates in each region correlated with subsequent declines in infection among unvaccinated young adults.

“On average, for every 20 percentage points of vaccinated individuals in a given population, the proportion of positive testing for the unvaccinated population decreased by nearly double,” the researchers wrote.

Another recent study from Public Health England, which was published as a file Correspondence in the New England Journal of Medicine Last month, it was found that three weeks after people received a single dose of the Pfizer-BioNTech or AstraZeneca-Oxford vaccine, transmission of the virus at home was reduced by 40 to 50 percent.

Watch | An ICU doctor in Saskatoon describes regretting the death of an unvaccinated COVID-19 patient:

Dr. Hassan Al-Masry, an intensive care unit specialist based in Saskatoon, said one patient who died of COVID-19 was regretting not having received a vaccine against the virus. 0:45

The spread of the virus thanks to the variables

But while vaccinated individuals may help protect those who did not receive the full set of injections, these efforts go too far.

Across Africa, where vaccination rates are among the lowest in the world, variants such as delta, alpha and beta are spreading rapidly, leading to high infection rates and stressing hospital systems in various countries.

The World Health Organization said Thursday that the entire continent has seen a 43 percent rise on a weekly basis in Covid-19 deaths, with at least six countries now facing a shortage of intensive care beds.

“We really need to get things in order soon, because the simple fact is that areas that may actually have been delayed somewhat from the pandemic so far are now taking a very hard hit,” said Jason Kendracchuk, associate professor of viral pathology. at the University of Manitoba.

“South Africa is an excellent example where they have low vaccine coverage. This is the most prosperous country in Africa, they’ve already been hit by the gamma variant, and now they’re being hit again by Delta.”

The delta variant, which is thought to be significantly more transmissible than other widely distributed variants and the original strain of SARS-CoV-2, is also circulating even in highly vaccinated countries such as Israel, the United Kingdom, the United States, Canada and It now accounts for nearly 75 percent of cases in Ontario alone.

However, in all of those countries, daily deaths have decreased significantly since the vaccination efforts began.

unprotected transmission

However, there remain pockets of unvaccinated individuals – whether due to eligibility, hesitation or lack of access – and there is a stark division in how this virus is now affecting people’s lives, with unprotected individuals bearing the brunt of its spread.

In the United States, for example, nearly all COVID-19 deaths are among those who have not been fully vaccinated, According to an Associated Press analysis.

There are growing concerns about that High number of cases in states with low vaccination rates — like Missouri, Arkansas, Nevada, Louisiana, and Utah — could be a harbinger of more hospitalizations and deaths in those specific regions, even if the United States as a whole avoids a massive spike.

“If there’s a large proportion of people who are not vaccinated — and that’s exactly what we’re seeing in the United States — these are going to be the people who are primarily driving transmission, these are going to be the majority of cases, those are going to be the vast majority of hospitalizations and deaths.”

listen | What can the rest of Canada learn from the wave of COVID-19 in the Yukon?

It’s a similar situation in Canada as well.

In Saskatchewan, COVID-19 patients who were recently admitted to the county’s intensive care units have not been vaccinated. In June, 15 people died from the virus, and officials said none of them had been fully vaccinated.

And the spread of the variable gamma outbreak that swept through the heavily fortified Yukon provides a cautionary tale. As of June 6, the area had recorded fewer than 90 cases, but that has since risen to more than 460 – the largest outbreak the North has seen – and they are largely among those not fully vaccinated.

Kindrachuk said intermittent vaccine coverage could mean these disparities persist in the coming months, because communities with lower vaccination rates “do not have this protective barrier” against more transmissible variants even if overall vaccination levels rise.

“Ultimately, the vaccines were working very well,” he said.

“It’s rather a question of, how do we distribute it globally to the regions where we’re seeing high transmission and reduce that number?”