Got a cold? It could protect you from other viruses — but only for a bit

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Infectious disease experts say having one virus like a common cold could keep others at bay, as each bug effectively takes turns over the fall and winter.

Respiratory syncytial virus, or RSV, infections are stabilizing across the country and flu is picking up sharply, according to the Public Health Agency of Canada. 

Canadians are mingling and travelling freely again. The mixing of people with each other gives scientists a rare opportunity to watch how the different respiratory pathogens we carry interact after a pandemic.

Until now, most virus research has focused on just a single pathogen at a time, whether in an individual patient or a whole population.

Here's a look at the early science into why we likely won't see multiple viruses hitting adults at the same time — and who may be more vulnerable to a double- or triple-whammy.

Though the idea of viruses interfering with one another has been discussed since the 1960s, the 2009 H1N1 influenza pandemic gave scientists some further clues about it.

Dr. Guy Boivin, a virologist and professor of pediatrics at Laval University in Quebec City, wrote a commentary earlier this year reviewing the evidence on viral interference — competition between respiratory viruses interfering or blocking each other's spread.

"It was notable that the [H1N1 flu] pandemic virus emerged in France two to three months after its emergence in the other European countries," Boivin said. "That was related to a rhinovirus outbreak at that time. This small epidemic of rhinoviruses delayed the pandemic H1N1 virus in France."

Rhinovirus is a type of a common cold virus.

When it comes to waves of different respiratory infections like COVID, RSV and flu circulating in Canada, Boivin said he expects some overlap. But he also thinks it's unlikely they will all peak at the same time, because catching one bug can offer short-term protection against other viruses.

Dr. Ellen Foxman, an immunologist at the Yale School of Medicine in New Haven, Conn., studies antiviral defences at her lab, including how viral interference happens.

"Having one virus activates antiviral defences in your body," Foxman said. "That can protect against other viruses too, at least for a short span of time."

Foxman said it's possible that having one infection makes you less likely to get another at the same time. For instance, if human airway tissues are infected with rhinovirus and then the H1N1 flu is introduced a few days later, the influenza virus won't grow.