With a "tripledemic" of Covid-19, flu, and respiratory syncytial virus emerging this winter, people's immune systems "can only offer so much protection," and more people are likely to get sick from multiple viruses this year, Jacob Stern writes for The Atlantic.

A 'tripledemic' is on the horizon

Over the last few weeks, cases of Covid-19, flu, and RSV have continued to grow, leading to concerns about a potential "tripledemic" of respiratory viruses in the United States this winter.

Although Covid-19 cases and hospitalizations are still lower than they were earlier in the pandemic, around 350 people are still dying from the disease every day. In addition, new variants that are driving surges around the world, such as BQ.1 and BQ.1.1, are growing in prevalence in the United States, making up roughly 35% of all cases in the country as of Nov. 5.

Flu cases have also been surging in recent weeks, with hospitalizations hitting their highest rates in a decade. According to CDC, nine states, New York City, and Washington, D.C. reported very high activity of influenza-like illnesses for the week ending in Oct. 29, while eight states reported high activity and four states reported moderate activity.

On top of growing Covid-19 and flu cases, RSV cases have also been on the rise, particularly among young children. RSV is a common and typically mild illness, but it can lead to pneumonia and bronchiolitis in young children and can be life-threatening to infants and young adults.

According to CDC data, RSV cases are rising in eight out of 10 HHS regions, with Midwestern states, including Minnesota, Nebraska, Missouri, and Wisconsin, seeing the highest positivity rates. Currently, pediatric hospitals across the country are struggling to keep up as RSV cases continue to rise.

"Pediatric hospitals are in crisis mode right now," said Lisa O'Connor, senior managing director at FTI Consulting. "They are pulling out emergency preparedness policies and activating everything functionally possible from a policy and regulatory standpoint."

Will your immune system hold up against all these viruses?

With so many viruses currently circulating, people can likely expect to encounter one or more of them at some point this winter. "When you board a plane, or see a show, or eat out, you're facing a more varied swirl of viruses than in recent years," Stern writes. "How should you expect your body to cope?"

In general, the immune system is "famously complicated," Stern writes, which means that how one person reacts to a particular virus will not be the same as someone else. Several factors, including genetics or whether someone is immunocompromised, will come into play.

When a virus first enters your body, it will encounter the innate immune system, or "a constellation of cells, barriers such as our skin, and reflexes such as coughing that work in concert to ward off foreign invaders," Stern writes.

However, the innate immune system is not very discerning, and being infected by one virus is unlikely to increase the innate immune system's response to another.

"You might be a little revved up, and your immune system might work a little bit faster, but there's no specific protection," said Cindy Leifer, an immunologist at Cornell University. "You're still going to get the whole infection. It might just be a little less severe."

In addition, an infection by one pathogen can sometimes leave you vulnerable to infection by another, according to Annabelle de St. Maurice, a pediatric infectious disease specialist at UCLA Health. For example, flu can increase the risk of certain bacterial infections, and Covid-19 can increase the risk of certain fungal infections.

Aside from the innate immune system, there is also the adaptive immune system, which includes B and T cells. These cells are capable of remembering past pathogens, which allows the body to respond more quickly and robustly if the same pathogen is encountered again.

In certain situations, adaptive immunity against one pathogen may end up also protecting against another pathogen if the two are sufficiently similar. This cross-reactive immunity has sometimes occurred with different flu strains or Covid-19 variants when the body recognizes a part that is shared by different pathogens.

However, cross-reactivity is not guaranteed and can differ drastically between individuals. Although researchers are trying to understand why cross-reactivity occurs in one person and not another, they don't "really have a good handle on that" yet, Leifer said.

Overall, "the reality is that you're more likely to get sick with multiple different things this winter than you were in either the last one or the one before," Stern writes. "… Your immunological superpowers can only offer so much protection."

How to protect yourself from respiratory viruses

To reduce the risk of infection, health experts have offered several tips, including:

• Wearing a mask
• Keeping physical distance from others
• Washing your hands regularly or using hand sanitizers
• Sanitizing high-contact surfaces, such as tables, desks, and doorknobs if someone in your household is sick
• Getting vaccinated against flu and Covid-19

In addition, if you or your child gets sick, you should stay home from work or school to avoid spreading the virus to other people.

"Whatever people can do to mitigate spread of any virus that would require hospital care I think we should do, because the hospitals are so strained," said Scott Roberts, associate medical director for infection prevention at Yale New Haven Hospital. (Stern, The Atlantic, 11/8)