COVID infection: Still questions about preventing transmission

After more than two years of COVID-19 and millions of cases, the question of why some people get infected and others don’t remains a mystery.

While many factors will determine whether a person gets sick, preventing someone from contracting the virus in the first place is something that researchers are continuing to work on.

Since their launch, COVID-19 vaccines have been shown to effectively prevent serious illnesses requiring hospitalization and death, although their effectiveness declines over time and who gets vaccinated. strains can still contract the virus, as is evident in the winter wave of Omicrons of varying transmissibility.

Health officials also warn of a recent increase in cases, possibly due to a combination of sub-BA.2, weakened immunity and the lifting of some acute pandemic restrictions. province, including regulations on masks.

The latest data from the Public Health Agency of Canada shows that the number of people hospitalized for COVID-19 in Canada is still much lower than it was during the Omicron wave, but the number of hospitalizations is increasing gradually.

Here’s what we know about the factors that can lead to COVID-19 infection and underlying disease, and what recent studies say on the matter.


When it comes to infections and diseases, Dr Donald Vinh, an infectious disease specialist at McGill University Medical Center in Montreal, notes that there are many steps involved.

First, a person needs to be infected, which means they have been exposed to the virus and it has entered their cells.

After that, a person may be asymptomatic, have mild symptoms, or develop a more severe or life-threatening illness.

Vinh is a member of an international organization called the COVID Human Genetic Effort that is trying to understand why some people develop severe illness – and what treatments can help – and why others have it. may not be infected, a problem he describes as the “Achilles heel” of the pandemic.

Pointing to a possible genetic component, he said the virus attaches to a range of proteins on the cell. The theory is that some people may carry different protein variants, making them less attractive to the virus.

“We all have genetic differences. He told in a phone interview on Monday.

Eleanor Fish, a professor of immunology at the University of Toronto and a scientist with the University Health Network, told in a phone interview Monday that many factors will influence transmission.

But the most important feature, aside from the virus itself, is a person’s immune status.

Elderly people have less powerful immune systems than adults and children.

And although children’s immune systems are much less “educated” than adults, Fish says the immune response leans more toward what’s known as innate immunity.

“It’s already primed and activated in certain respects, so they’re better equipped to deal with infections very quickly than adults,” Fish said.

But because children have smaller airways, this may explain why more children are hospitalized with COVID-19, she added, as Omicrons tend to support the upper airways rather than the lungs.

Fish also showed an interferon response, or proteins that help the body create an innate and early immune response to clear the virus.

Some viruses like SARS-CoV-2 have evolved to specifically block or inhibit the production of these interferons, which can lead to more severe infections, she said.

For example, a child’s interferon response can be triggered fairly quickly, but genetic mutations can lead to more severe disease.

Many immune response genes are also located on the X chromosome, which may explain why women have a stronger innate immune response than men, Fish said.

Fish also points to the importance of antiretroviral drugs in the process of helping to stop transmission, especially in vulnerable settings such as long-term care homes.

“I think this is a really important strategy that we’re not taking seriously,” she said.

A recent trial in which volunteers were intentionally exposed to the new coronavirus found that symptoms did not affect the likelihood that an infected person would transmit the disease to others, according to Reuters.

In January, a pre-print study presented some preliminary evidence that the coronavirus loses most of its infectivity after 20 minutes in the air.


Age and pre-existing medical conditions are among the highest risk factors for developing more severe illness from SARS-CoV-2, the coronavirus that causes COVID-19.

Older adults, especially those over 60, account for more hospitalizations and deaths from COVID-19 than younger age groups.

As of April 1, 2022, the Public Health Agency of Canada reports that while more than half of all reported cases of COVID-19 involve people under the age of 60, older people have accounts for nearly two-thirds of all hospitalizations and many of the majority of deaths.

Certain chronic medical conditions, including lung and heart disease, hypertension or high blood pressure, diabetes, kidney and liver disease, dementia, and stroke, can lead to worse outcomes.

People who are immunocompromised due to an underlying medical condition such as cancer or because they are receiving chemotherapy may have a lower immune system. Obese people are also at higher risk.

In Sweden, a study published at the end of March in the medical journal The Lancet, found that the risk of COVID-19 re-infection and hospitalization in people who had previously recovered remained low for 20 years. month. Natural immunity plus one or two doses of the COVID-19 vaccine continued to reduce risk for up to nine months, although researchers say the difference in absolute numbers is very small .

Evidence has also emerged that the body’s T-cell response, which can help fight viral infections as part of the immune system, is effective in mitigating COVID-19 disease.

T cells can be made from previous vaccinations and infections.

A small study from January found that exposure to a common cold virus may provide some protection.

In November, British researchers published a study showing that a small group of healthcare workers, possibly exposed to COVID-19, did not develop antibodies but produced a broad T-cell response. widely, suggesting that the T cells cleared the virus before any symptoms or positive test results were present.

Vinh said that T cells do not necessarily prevent infection but reduce disease.

Some T cells help B cells, which are also part of the immune system, to make more mature antibodies, while others follow virus-infected cells.

As for why some people get very sick and others don’t, he said evidence shows that elderly men in particular have an unstable immune response, for reasons that are not clear, they carry natural autoantibodies that specifically attack type 1 interferon proteins associated with the body. immune response.

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