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Even if highly contagious variants of the coronavirus are spreading, virologists and immunologists say that leading vaccines can not only prevent serious infections, they may also inhibit the spread.
However, this does not mean that vaccinated people can completely protect the unvaccinated — billions of people worldwide — especially in areas with low vaccination rates.
Akiko Iwasaki, professor of immunobiology at Yale University School of Medicine, said: “Most vaccines are very effective in preventing the spread from vaccinated infected people to unvaccinated people.”
In various countries where vaccination is widely carried out, there are some other obvious trends: Severe COVID-19 cases are declining As the vaccination rate rises; “breakthrough infection” in fully vaccinated individuals Remain rare and usually mild; And cases of serious illness leading to hospitalization or death are now Mainly in people who have not been vaccinated.
As most of the world, including Canada, reopened, all this supported the protective capabilities of the first vaccines.
Iwasaki said, but because there are so many unvaccinated people in the world, and because of the transmissibility of variants such as delta, the virus continues to spread.
“The whole concept behind herd immunity is to provide protection for unvaccinated people by having enough vaccinated people around them,” she said.
“But I don’t think we can be complacent, because this kind of herd immunity does require vaccinating a large number of people in a specific population. This has not been done in many places.”
Few fully vaccinated COVID-19 cases
In Canada, the number of COVID-19 cases has dropped sharply in recent months, And the data only shows a small part of it Is one of the Canadians who are fully vaccinated.
But because more than half of the population has not yet been fully vaccinated, millions of people are still at risk of infection.
Although several experts who spoke to CBC News stated that vaccinated individuals are helping to contain transmission to those who are not yet protected, the exact mechanism by which the COVID-19 vaccine may reduce transmission is not fully understood.
Angela Rasmussen, a virologist at the University of Saskatchewan’s Vaccines and Infectious Diseases Organization, said that vaccines are not like walls or shields that completely prevent the virus from entering your body, but more like a complex Once the invaders arrive, they will repel them.
For example, she said, imagine someone coughing on your face. Whether you are vaccinated or not, you will inhale some virus particles. But for those protected by the vaccine, what happens next will be different.
Watch | As the number of cases increases, the vaccination rate in the United States has slowed:
Iwasaki said that the immune system of the vaccinated individual is fighting the virus faster, making it almost impossible to replicate, and minimizing symptoms that help spread the virus, such as coughing or sneezing.
She said: “We know that this type of activity can better promote and expel the virus than just breathing.”
Rasmussen said that because fully vaccinated people are usually able to clear the infection so quickly, they are “very unlikely” to produce enough virus to infect others.
More research is needed to measure the impact on transmission
Rasmussen said that although these are the principles of how vaccines prevent infection and spread, it is actually tricky to obtain real-world data to determine how much they inhibit the spread of the virus. With the continuous development of SARS-CoV-2 , More research is needed to evolve.
The team behind a recent study on Israeli vaccine protection acknowledged these challenges, saying that their study has several key limitations. Individual behavior, policy decisions such as lockdowns, and post-infection immunity are all messing up the water-making it more difficult to figure out how many vaccines have prevented the virus from spreading.
Nevertheless, after taking all these factors into consideration, the researchers did find that “observational evidence shows that vaccination not only protects vaccinated individuals, but also provides cross-protection for unvaccinated individuals in the community.” Their peer-reviewed briefing published in the June issue of Nature.
The team analyzed the vaccination records and test results collected during the rapid launch of vaccines in 177 communities and found that the vaccination rate in each area was related to the subsequent decline in the infection rate of unvaccinated youth.
The researchers wrote: “On average, for every 20 percent of vaccinated individuals in a specific population, the positive test scores of unvaccinated people drop by about twice.”
Another recent study comes from Public Health EnglandAs Correspondence in the New England Journal of Medicine Last month, it was discovered that three weeks after people received a single dose of Pfizer-BioNTech or AstraZeneca-Oxford vaccines, home transmission of the virus was reduced by 40% to 50%.
Watch | Saskatoon ICU doctors describe their regrets about the death of COVID-19 patients who were not vaccinated:
The virus spreads due to mutation
But while people who have been vaccinated may help protect those who have not received the full set of vaccines, these efforts only stop there.
In most parts of Africa, the vaccination rate is the lowest in the world, mutations such as delta, alpha, and beta are spreading rapidly, and the infection rate is soaring, putting pressure on the hospital systems of various countries.
The World Health Organization said on Thursday that across the African continent, COVID-19 deaths have increased by 43% every week, and at least six countries are now facing a shortage of intensive care beds.
Jason Kindrachuk, assistant professor of virus pathogenesis, said: “We need to really contain the situation as soon as possible, because the simple fact is that so far, those areas that may have actually been relieved from the pandemic are now affected. Very serious blow.” At the University of Manitoba.
“South Africa is a perfect example. Their vaccine coverage is very low. This is the most prosperous country in Africa. They have been attacked by the gamma variant and are now attacked by delta.”
The delta variant is considered to be more transmissible than other widely spread variants and the original strain of SARS-CoV-2, even in countries with high vaccination rates such as Israel, the United Kingdom, the United States and Canada, it is also circulating. Now in Ontario alone, it accounts for nearly 75% of cases.
However, in all these countries, the number of daily deaths has dropped significantly since the start of vaccination efforts.
Unvaccinated “driving transmission”
However, there are still a small number of people who have not been vaccinated—whether because of qualifications, hesitation, or accessibility—and there are clear differences in how the virus affects people’s lives now, with unprotected individuals bearing the brunt.
For example, in the United States, almost all deaths from COVID-19 are now in people who are not fully vaccinated. According to the Associated Press analysis.
People are getting worried Increased number of cases in states with low vaccination rates Missouri, Arkansas, Nevada, Louisiana, and Utah-may be a harbinger of more hospitalizations and deaths in these specific areas, even if the United States as a whole has avoided a massive surge.
“If a large percentage of people are not vaccinated-which is what we are seeing in the United States-these people will be the main drivers of transmission, those will be the majority of cases, and those will be the vast majority of hospitalizations and deaths. Case,” Rasmussen said.
Listen | What can the rest of Canada learn from the COVID-19 wave in the Yukon?
10:34What can the rest of Canada learn from the current COVID-19 wave in the Yukon?
A similar situation exists in Canada.
In SaskatchewanThe vast majority of COVID-19 patients who have recently been admitted to the province’s ICU have not been vaccinated. In June, 15 people died from the virus, and officials said none of them were fully vaccinated.
An outbreak caused by a gamma mutation sweeping the world Yukon is heavily vaccinated A cautionary story is also provided. As of June 6, fewer than 90 cases had been recorded in the region, but since then it has soared to more than 460 — the largest outbreak experienced in the north — and most of them have not been fully vaccinated.
Kindrachuk said that uneven vaccine coverage may mean that these differences will continue to exist in the coming months, because even if overall vaccination levels rise, communities with lower vaccination rates “do not have that protective buffer”. Resist more spreadable mutations.
“In the end, the vaccine works very well,” he said.
“The more question is, how can we distribute these viruses globally to areas where we see high transmission and reduce losses?”