Here's why flu and RSV are on the rise right now, and how COVID itself may have affected our immune systems.
This year's flu season is shaping up to be particularly bad, with the current weekly number of cases at extraordinarily high levels. Meanwhile, doctors are seeing an increase in respiratory syncytial virus, better known as RSV, which usually causes mild, cold-like symptoms in adults but can be especially dangerous for very young children and the elderly. This increase in RSV has already led to an unusually high number of hospitalizations, especially in young children. These spikes in influenza and RSV infections are happening earlier in the year and at higher than normal levels.
There are many unknowns as to why influenza and RSV are at unusually high levels. "Your immune system is not like a muscle, where if you don't use it, you lose it."
If the culprit isn't that we've been wearing masks for an entire year, then what do we know about why this year's flu and RSV season is higher than usual?
How does our immune system work?
"Our immune system isn't atrophying, it's not weakening, it's functioning on a daily basis," said Sabina Vohra-Miller, founder of Unambiguous Science. As Vohra-Miller points out, although respiratory viruses like the flu declined in the 2020-2021 season, our immune systems are constantly exposed to pathogens in our food and water, most of which never cause disease. As we age, our immune systems will begin to decline, similar to how photos wrinkle as we age.
However, "in children and healthy adults, if they don't have some type of immunocompromised health condition, those photos remain very much intact," Furness said. "It doesn't matter that you haven't had the flu in years, your body will respond to the flu like it did last time."
With a virus like the flu, it can evade the immune system only by changing to the point where it is no longer recognisable, while for viruses and pathogens that change little, like measles or chicken pox, the immune system will be able to fight off the first time, the next time an exposure occurs, even if it's been years.
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 the reason why we are seeing such high numbers of influenza and RSV . “There is some truth to the notion that due to pandemic restrictions curbing all types of respiratory diseases, we are seeing a resurgence of them, generally,” Deonandan said.
However, this resurgence has to do with the seasonality of viruses like influenza and RSV, rather than a lack of infections affecting a person's immune system. As predicted by several scientists in a 2020 paper, the low number of respiratory infections, combined with the seasonality of these viruses, can lead to higher-than-usual infections in later seasons.
Now, with the return from school, "it really reignited the viruses within the school environment," said Pedro Piedra, a virologist at Baylor College of Medicine. All of these viruses circulating among schoolchildren have the knock-on effect of infecting others in their social circles, such as their parents, who then pass it on to their peers.
COVID infections can affect our immune system
This is not a new idea – there are a number of viruses known to negatively impact our immune systems. An example is the measles virus, which can make our immune system "forget" about past infections. As a 2019 study showed, a measles infection can have the effect of eliminating between 11 and 73 percent of the antibodies in our bodies.
It is not yet known how much COVID may reduce the response of our immune system, who may be susceptible and what the effects may be. "Many people have had multiple infections and are doing well," Deonandan said.
To reduce the risk, use precautionary measures
Influenza causes between 12,000 and 52,000 deaths per year and RSV causes between 58,000 and 80,000 hospitalizations per year in children under 5 years of age. While this year is on track to be particularly bad, the risks are well defined.
"None of this is new."
The upside is that there are a number of precautionary measures that can reduce your risk of getting sick or lessen the severity of these symptoms. This includes staying up to date with COVID vaccinations, making sure you get your flu shot, and taking precautionary measures, like wearing a mask, when in a crowded environment.