More than two years into the pandemic, many in Canada and around the world have remained COVID-19 free – or at least, have not tested positive for it.

In Canada, nearly 3.5 million coronavirus cases have been reported, which is nine per cent of the total population — but what about the rest?

Experts say due diligence with public health measures, the power of vaccination and a little luck have kept many COVID-19 free.

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“To not get COVID, you have to be careful, meticulously careful and also fortunate,” said Colin Furness, infection control epidemiologist and assistant professor at the University of Toronto.

Your location and living arrangement can increase the likelihood of catching COVID-19, with studies showing that marginalized communities are at greater risk of infection.

Genetic factors, that have not yet been identified, could also be playing a role with some people being simply impervious to COVID-19, said Furness.

That can also explain why people have different reactions to the virus and experience varying symptoms.

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International researchers are trying to determine which genes are potentially resistant to SARS-CoV-2, the virus that causes COVID-19.

“There are some diseases that are clearly linked to one gene, but in many cases, it’s far more complicated and there might be multiple pathways,” said Furness.

There are seven known coronaviruses that can infect humans, including the common cold.

Previous exposure to other forms of coronaviruses can keep someone from catching COVID-19, said Dr. Horacio Bach, an infectious diseases expert at the University of British Columbia.

“These people develop antibodies, so when they are theoretically exposed to the virus, they can get rid of it very easily because of what we call cross-reaction,” Bach explained.

A study published in the Nature Communications in January suggested that having higher levels of pre-existing T cells that are created by the body when infected with other coronaviruses, can protect someone against COVID-19 infection.

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Another study published in November 2021 in the scientific journal Nature also showed that health-care workers in the United Kingdom who repeatedly tested negative for COVID-19 were able to fend off the virus because of the presence of T cells from exposure to previous seasonal coronaviruses.

Because much of the research for COVID-19 has been focused on those infected and how to treat them, experts say it is hard to exactly pinpoint why certain people have managed to evade the virus so far.

Getting to the bottom of this question could be a “real game-changer” in fighting the pandemic, said Furness.

“It’s possible that if we could figure out on what basis some people are immune, we might be able to develop effective drugs. We also might be able to just identify who’s at high risk.”