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Infectious disease experts say that having a virus like the common cold could keep others at bay, as each bug effectively returns in the fall and winter.
According to the Public Health Agency of Canada, respiratory syncytial virus, or RSV, infections are stabilizing across the country and the flu is on the rise.
Canadians mingle and travel freely again. The mixing of people together gives scientists a rare opportunity to see how the different respiratory pathogens we carry interact after a pandemic.
To date, most virus research has focused on a single pathogen at a time, either in an individual patient or in an entire population.
Here’s a look at the early science on why we probably won’t see multiple viruses hitting adults at the same time, and who might be most vulnerable to a double or triple whammy.
Several viruses may not affect adults at the same time, but children could face a double whammy or worse. Scientists are exploring how and when viruses interfere with each other. (BSIP/UIG/Getty)
The virus triggers the immune defense
Although the idea that viruses interfere with each other has been discussed since the 1960s, the 2009 H1N1 flu pandemic gave scientists some more clues about it.
Dr. Guy Boivin, a virologist and professor of pediatrics at Laval University in Quebec City, wrote a comment Earlier this year, reviewing the evidence on viral interference: competition between respiratory viruses that interfere with or block the spread of others.
“It was remarkable that the [H1N1 flu] The pandemic virus emerged in France two or three months after it appeared in the rest of the European countries,” said Boivin. “This was related to a rhinovirus outbreak at the time. This small rhinovirus epidemic delayed the H1N1 virus pandemic in France.”
Rhinovirus is a type of common cold virus.
When it comes to waves of different respiratory infections like COVID, RSV and flu circulating in Canada, Boivin said he expects there will be some overlap. But he also believes it’s unlikely they’ll all peak at the same time, because catching a bug can offer short-term protection against other viruses.
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Dr. Ellen Foxman, an immunologist at the Yale School of Medicine in New Haven, Connecticut, studies antiviral defenses in her lab, including such as viral interference happens
“Having a virus activates your body’s antiviral defenses,” Foxman said. “This may also protect against other viruses, at least for a short period of time.”
Foxman said it’s possible that having one infection makes you less likely to get another at the same time. For example, if human respiratory tract tissues are infected with rhinovirus and then H1N1 influenza is introduced a few days later, the influenza virus will not grow.
“It was because the defenses that the tissue activated in response to the rhinovirus also protected against the flu,” Foxman said.
He is currently looking at interference between the virus that causes COVID-19 and other viruses in human respiratory tract samples in his lab.
A view of Bichat Hospital where the French health ministry said a patient was treated for a confirmed case of pandemic H1N1 flu in May 2009. Scientists say another virus appeared to suppress H1N1 initially in France . (Benoit Tessier/Reuters)
Short-term protection
Foxman said the lining of our airways goes into an antiviral defensive state when they sense an invader.
The guard defense is one of several layers of protection of the immune system. One is called interferon: a family of proteins produced by the body’s immune system in response to an invasive viral infection.
As the name suggests, interferon interferes with or blocks the ability of a virus to achieve its purpose of making copies of itself.
Instead, interferon summons immune cells to the site of invasion so they can take up arms against the threat.
But interferon doesn’t stay activated for long, cautioned Dr. Allison McGeer, an infectious disease specialist at Sinai Health System in Toronto.
“It’s not an effect with most viruses and it’s not a big effect,” McGeer said.
Dr. Allison McGeer, an infectious disease specialist at Sinai Health System in Toronto, says the effect of viral interference is small. (Evan Mitsui/CBC)
The opposite can also happen. Some people have double infections or coinfections: two or more bugs at the same time.
Why this is so is not well understood and the degree to which it happens is just beginning to be explored.
McGeer said coinfections occur “not infrequently” among hospitalized children.
Multiple infections of the baby at the same time
Emilie Doré’s six-week-old son, Diego, was one of them. “My motherly instincts told me it was a bad cold with a baby who is too small, too young,” Doré recalled.
Baby Diego was hospitalized at the Montreal Children’s Hospital for four days with multiple respiratory infections. (Submitted by Emilie Doré)
Doré was looking for symptoms in the baby after her two-year-old daughter fell ill. First the baby had some congestion and a cough followed by lethargy and fever.
“I would say the most upsetting and worrying moment was when she had to put him on oxygen because he was having trouble breathing,” said the Montreal mom.
When it didn’t improve, Diego had a lumbar puncture or lumbar puncture. Tests suggested he had RSV, rhinovirus and enterovirus, another common cold virus, as well as possibly meningitis.
He recovered after four days in hospital and is now eight weeks old.
Baby Diego has recovered. (Submitted by Emilie Dore)
Virologists say that at the population level, other factors, such as human behavior of different age groups, population immunity, environmental conditions such as temperature and humidity, and what has happened during the COVID- 19 also influence the triple threat of viral spread.
Separate waves of each virus can still sicken people and increase demand on emergency departments and primary care services at a time when they are struggling with staff shortages and backlogs.
Dr. Gerald Evans, chair of infectious diseases at Queen’s University and Kingston Health Sciences Center, said when people in hospital are tested for respiratory infections now, three viruses can show up.
“We’re starting to get a little signal that people can get infected with both influenza and COVID, and certainly in children we’re seeing influenza and RSV emerging,” Evans said.
“So the impact of this co-infection we still have to figure out. We’re seeing it. It’s small numbers.”