This year’s flu season looks set to be particularly bad, with the current weekly case count at extraordinarily high levels. Meanwhile, doctors are seeing an increase in respiratory syncytial virus, more commonly known as RSV, which generally causes mild, cold-like symptoms in adults but can be especially dangerous for the very young and the elderly. This RSV spike has already led to an unusually high number of hospitalizations, especially in young children. These spikes in flu and RSV infections occur at an earlier time of year and at higher than normal levels.
There are many unknowns about why flu and RSV are unusually high. One thing is certain, though: “Just because we were wearing masks all this time, it didn’t mean we were harming our immune system,” said Raywat Deonandan, an epidemiologist at the University of Ottawa. “Your immune system isn’t like a muscle, where you lose it if you don’t use it.”
If the culprit isn’t us wearing masks for an entire year, what do we know about why the flu and RSV season is higher than normal this year?
How does our immune system work?
Our immune system is used much more than we realize, even when we don’t get sick. “Our immune system isn’t atrophying, it’s not weakening, it’s working on a daily basis,” said Sabina Vohra-Miller, the founder of Unambiguous Science. As Vohra-Miller points out, even though respiratory viruses like the flu were down in the 2020-2021 season, our immune systems are constantly exposed to pathogens in our food and water, the vast majority of which are never the result of illness.
Our immune system also has a very long memory, where it “acts like a photosystem,” says Colin Furness, an epidemiologist at the University of Toronto. “It’s very permanent.” Our immune system learns to recognize specific infectious agents it has seen before.
As we age, our immune system will begin to decline, similar to how photos wrinkle as we age. However, “in children, and in healthy adults, if you don’t have any kind of immunocompromised health condition, those pictures remain very much intact,” Furness said. “It doesn’t matter that you haven’t had the flu in years, your body will react to the flu the way it reacted last time.”
With a virus like the flu, it can only evade the immune system by changing beyond recognition, while with viruses and pathogens that don’t change much, like measles or chickenpox, the immune system will be able to fight it off the next time it happens. an exposure occurs, even if it was years ago.
Influenza and RSV are seasonal
While not being exposed to respiratory viruses for a year won’t affect a person’s immune system, the unusually low number of cases during the 2020-2021 season may be part of why we’re seeing such high numbers of flu and RSV. “There’s some truth to the idea that because of pandemic restrictions holding back all kinds of respiratory illnesses, we’re seeing a resurgence overall,” Deonandan said.
However, this resurgence has to do with the seasonality of viruses such as the flu and RSV, not a lack of infections that compromise a person’s immune system. As a number of scientists predicted in a 2020 paper, the low rate of respiratory infections, combined with the seasonality of these viruses, could lead to more than usual infections in later seasons.
Right now, with school back in business, “it has really revived the viruses in the school environment,” said Pedro Piedra, a virologist at Baylor College of Medicine. All of these viruses circulating among school children have the ripple effect of infecting others in their social circles, such as their parents, who then spread it to their peers.
COVID infections can affect our immune system
One factor that may be contributing to this year’s unusually bad flu and RSV seasons is the effect of a COVID infection on our immune system. As early evidence suggests, this may play a role. “There are a number of papers suggesting that COVID infection could reduce our ability to fight future infections from different species,” Deonandan said.
This is not a new idea: there are a number of viruses that are known to negatively impact our immune system. An example is the measles virus, which can cause our immune system to ‘forget’ previous infections. As a 2019 study showed, a measles infection can cause between 11 and 73% of our body’s antibodies to be destroyed.
It is not yet known how much COVID can reduce our immune system’s response, who may be susceptible and what the effects may be. “A lot of people have had multiple infections that are fine,” Deonandan said. “It’s only possible that some of the individuals will become infected or re-infected, and that compromises their ability to fight off future infections.”
Use precautions to reduce your risk
The flu causes between 12 and 52,000 deaths per year and RSV causes 58,000 to 80,000 hospitalizations per year in children under the age of 5. While this year is on track to be a particularly bad year, the risks are well established. “Respiratory viral infections, before the pandemic, during the pandemic and after the pandemic, will have a significant impact on our health,” Piedra said. “None of this is new.”
The upside is that there are a number of precautions that can reduce the risk of getting sick or reduce the severity of these symptoms. This includes staying up to date on your COVID vaccinations, making sure you get your flu shot, and taking precautions, such as wearing a mask, when in a crowded environment.
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