Buzz
This year's flu season is particularly severe, with weekly case numbers at unusually high levels. At the same time, a surge in respiratory syncytial virus (RSV) cases is being reported. While RSV typically causes mild, cold-like symptoms in adults, it can be more dangerous for young children and the elderly. This surge has already led to a notable increase in hospitalizations, especially among young children. The flu and RSV outbreaks are happening earlier and at higher levels than what’s typical for this time of year.
Though many uncertainties surround why flu and RSV cases are unusually high, one thing is clear: 'Wearing masks all this time didn’t damage our immune system,' explained Raywat Deonandan, an epidemiologist from the University of Ottawa. 'Your immune system isn’t like a muscle that you lose strength in if it’s not constantly active.'
If wearing masks for a year isn’t the cause of this year’s higher-than-usual flu and RSV levels, what do we know about what’s actually behind the surge?
What exactly is the role of our immune system?
Our immune system is constantly at work, even if we don’t feel sick. 'It’s not weakening or deteriorating; it’s active every day,' explained Sabina Vohra-Miller, founder of Unambiguous Science. Vohra-Miller notes that, even though respiratory viruses like the flu were less prevalent during the 2020-2021 season, our immune system is always dealing with pathogens found in food and water—most of which don’t cause illness.
Our immune system has an exceptional memory, 'it functions like a photo system,' said Colin Furness, an epidemiologist at the University of Toronto. 'It’s very durable.' The immune system learns to recognize pathogens it has encountered before.
As we age, our immune system weakens, much like photos fading over time. However, 'in children and healthy adults—unless there's an underlying immunocompromised condition—those 'photos' remain intact,' Furness explained. 'Even if you haven’t had the flu in years, your body will respond to it just as it did the last time.'
For viruses like the flu, the immune system can only be evaded if the virus changes enough to be unrecognizable. But for viruses and pathogens that don’t alter much, like measles or chickenpox, the immune system will be able to combat them again, even after many years.
Flu and RSV follow seasonal patterns
While not being exposed to respiratory viruses for a year doesn’t harm a person’s immune system, the unusually low number of cases during the 2020-2021 season may be contributing to the current surge in flu and RSV cases. 'There is some truth to the idea that pandemic restrictions, which limited all kinds of respiratory illnesses, have led to their general resurgence,' said Deonandan.
However, this resurgence is more tied to the seasonal nature of viruses like the flu and RSV, rather than a weakened immune response from fewer infections. As several scientists predicted in a 2020 study, the low levels of respiratory infections, combined with these viruses’ seasonal tendencies, are likely leading to higher-than-normal infection rates in the following seasons.
With schools now back in session, 'it’s really reigniting the spread of viruses within the school setting,' explained Pedro Piedra, a virologist at Baylor College of Medicine. The circulation of these viruses among schoolchildren creates a ripple effect, spreading to their families and then to their colleagues.
COVID infections may be impacting our immune system
One potential factor behind this year’s particularly severe flu and RSV seasons is the impact of a COVID infection on our immune systems. Early evidence suggests this might be contributing. 'Several studies indicate that a COVID infection could impair our ability to defend against future infections of various types,' said Deonandan.
This isn’t a new concept: there are several viruses known to negatively affect our immune system. For instance, the measles virus is known to cause our immune system to 'forget' previous infections. A 2019 study showed that a measles infection could result in the loss of anywhere from 11 to 73% of our body’s antibodies.
It remains unclear how much COVID may weaken our immune system response, who might be most affected, and the full extent of these effects. 'Many people who’ve had multiple infections are just fine,' Deonandan said. 'But there may be a portion of individuals who get infected or reinfected, and that could compromise their ability to fend off future infections.'
Take precautions to lower your risk
Flu results in between 12,000 to 52,000 deaths annually, while RSV leads to 58,000 to 80,000 hospitalizations per year among children under 5. While this year is expected to be particularly severe, the risks are well-known. 'Respiratory viral infections—before, during, and after the pandemic—will continue to significantly affect our health,' Piedra said. 'This isn’t new.'
The benefit is that there are various precautionary actions you can take to reduce the likelihood of falling ill or to minimize the severity of symptoms. These include keeping up with your COVID vaccinations, ensuring you get your flu shot, and adopting preventive measures like wearing a mask in crowded settings.
