In 2020, and once more in 2021, the dreaded twindemic by no means got here. The concern amongst specialists was {that a} winter COVID surge layered on prime of flu season—and even, in worst-case eventualities, a flu outbreak of pandemic proportions—would push already strained hospitals to the brink. Fortunately, we received fortunate. Flu season merely didn’t materialize in 2020: America recorded solely about 2,000 circumstances, a jaw-dropping 110 occasions fewer than it had the season prior. Related traits held for different respiratory viruses. In 2021, cases had been means up from 2020, however nonetheless means down from typical pre-pandemic years.
Now our luck appears lastly to have run out. Flu season has solely simply begun, and already the U.S. has recorded an explosion of cases. An enormous wave of RSV is hitting the nation, together with smaller parallel surges in rhinovirus and enterovirus. The results of all that is what my colleague Katherine J. Wu has called “the worst pediatric-care disaster in a long time.” In the meantime, COVID circumstances and hospitalizations stay low across the nation relative to earlier phases of the pandemic, however the coronavirus continues to kill about 350 Individuals day by day. The concern now shouldn’t be a twindemic however a “tripledemic.”
What this implies for you is that your physique is prone to encounter a number of completely different virological foes this season—maybe even on the identical time. Whenever you board a airplane, or see a present, or eat out, you’re dealing with a extra diverse swirl of viruses than lately. How must you count on your physique to manage?
Earlier than delving into immunological arcana, it’s price making one factor completely clear, on the threat of stating the plain: Having a chilly won’t shield you from COVID. COVID won’t shield you from the flu. Nor the flu from RSV. Completely different viruses penetrate the physique’s defenses in several methods, and sadly, as spectacular as our immune system is, it doesn’t have some common potential to fend off all seasonal pathogens just because it detects one. The identical goes for vaccinations. A flu vaccine won’t inoculate you towards COVID, and a COVID vaccine won’t inoculate you towards flu; defending towards each viruses requires each vaccines.
The immune system is famously difficult, nevertheless. As my colleague Ed Yong has written, immunology is where intuition goes to die. When folks’s our bodies face two completely different pathogens, whether or not concurrently or in fast succession, all types of dynamics consider. And extra complicated nonetheless, these dynamics can differ drastically from one particular person to the subsequent. Some folks have situations that go away them immunocompromised. Others should take immunosuppressive medicines. Genetics come into play. Elements that nobody but understands come into play.
When a pathogen finds its means into your physique, the preliminary phases of the response are a part of what’s known as the innate immune system—a constellation of cells, boundaries resembling our pores and skin, and reflexes resembling coughing that work in live performance to thrust back international invaders. The innate immune system shouldn’t be significantly discerning. It distinguishes solely between what’s a part of the physique and what’s not, then assaults the latter. An infection by one pathogen is unlikely to spice up the innate immune system’s response to a different in something however probably the most marginal means. “You may be somewhat bit revved up, and your immune system would possibly work somewhat bit quicker, however there’s no particular safety,” Cindy Leifer, an immunologist at Cornell College, instructed me. “You’re nonetheless going to get the entire an infection. It simply may be rather less extreme.”
These minor advantages, for those who get them in any respect, will possible final solely per week or two, she stated. And even they’re removed from a given. In truth, an infection with one pathogen can generally go away you extra weak to an infection with one other, Annabelle de St. Maurice, a pediatric-infectious-disease specialist at UCLA Well being, instructed me. Flu, for instance, can improve your threat of sure bacterial infections. COVID can improve your threat of sure fungal infections. At this level, it’s arduous to say how COVID will work together with different respiratory viruses. As a result of we’ve seen so few circumstances of those different viruses over the previous few years, we don’t have a lot of a pattern from which to make inferences.
Whereas the innate immune system hammers away, the physique musters B cells and T cells, which, not like the cells concerned within the innate immune response, are available many sorts specialised to struggle many alternative pathogens. These cells are a part of the adaptive immune system, distinguished from the innate response each by this specificity and by its capability for reminiscence. As soon as they’ve cleared a pathogen, a fraction of the B and T cells known as into motion stick round, in order that if the physique encounters the identical pathogen once more, it could mobilize extra swiftly and extra robustly than it did the primary time.
In sure circumstances, the adaptive immunity conferred by one pathogen can find yourself defending us from one other. That is known as cross-reactive immunity. If two pathogens are sufficiently comparable, the immune system would possibly construct safety towards one by preventing the opposite. We generally see this with completely different strains of the flu. Or completely different COVID variants. Because of this smallpox vaccines can inoculate towards monkeypox. Early on within the pandemic, some scientists hypothesized that previous infections with the common-cold coronaviruses so acquainted to us all would possibly present a level of safety towards COVID. Some research have supplied modest assist for this idea, however the real-world outcomes—hundreds of thousands of deaths from COVID-19—recommend that no matter safety we had wasn’t terribly robust, Donna Farber, an immunologist at Columbia, instructed me.
How cross-reactivity performs out can differ drastically from individual to individual. The response depends on the adaptive immune system recognizing part of pathogen A that pathogen B shares. It’s this matching that enables the physique to mount an immune response to pathogen B, regardless of having by no means encountered it earlier than. If the physique as a substitute acknowledges part of pathogen A that pathogen B doesn’t share, the physique received’t mount a cross-reactive response. Researchers are attempting to know why these dynamics happen a technique in a single particular person and in a different way in one other, however for the second, Leifer instructed me, “I don’t suppose we actually have an excellent deal with on that.”
When the physique occurs to strike upon a near-perfect match between elements of two viruses that in any other case aren’t all that comparable, she stated, it’s “like profitable the lottery.” Until you want these odds, you most likely shouldn’t financial institution on cross-reactive immunity bailing you out this flu season. As a substitute, the fact is that you just’re extra prone to get sick with a number of various things this winter than you had been in both the final one or the one earlier than. Be safe out there. Your immunological superpowers can solely provide a lot safety.
