Catch 1 Flu, Get 1 Free

Sometimes, having been infected with one virus will grant you immunity against a similar virus—as was famously the case with cowpox and smallpox, which led to the smallpox vaccine being developed.

If you are one of today’s lucky 10,000, then check out: WHO | History of smallpox vaccination, and the only human disease to have been eradicated so far

However, sometimes, getting one virus will just result in it inviting its cousin to come stay too!

The viral bonus (the bad kind)

Researchers (Dr. Alesandra Rodriguez et al.) found that exposure to one influenza strain can weaken one’s antibody response to a different strain encountered later.

Specifically, she and her team examined immune responses to two common influenza A subtypes (H3N2 influenza A and H1N1 influenza A) which frequently circulate in humans and cause seasonal flu.

The reason this happens is more interesting than you might expect, though. It’s not merely a case of “the immune system has taken a beating, so it works less well”. No, this happens even when the immune system has already fully recovered from the first one!

Rather, the effect, called immune imprinting (also known more colorfully as “original antigenic sin“), occurs when your immune system strongly remembers its first exposure to a virus, and reuses that response against related viruses even when it isn’t optimal.

For example, after the first infection, memory B cells rapidly produce antibodies during later exposures, but these antibodies may bind the new virus without effectively neutralizing it and can even interfere with the creation of a new, stronger immune response.

This goes down even to the molecular level, as structural analysis showed that even just a single amino-acid difference in the stalk epitope could dramatically reduce the effectiveness of many antibodies generated.

As a limitation, this was a pediatric study, but it’s expected that this will work the same way the same in older people too—the science just hasn’t been done yet to check.

You can read the paper in full, here: B cell imprinting in children impairs antibodies to the haemagglutinin stalk

So, what to do about it?

We’ve previously written about avoiding respiratory infections in general, for example: Why Some People Get Sick More (And How To Not Be One Of Them)

And for some specific key things to do:

• Being outdoors is better for reducing flu transmission than being indoors
  • In other words, do avoid enclosed spaces with lots of people where possible, because this is a big factor. In fact, while people think of cold weather as increasing the risk of colds and flu, the main real difference comes from “when it’s cold, people spend more time indoors in close quarters together with the windows closed”. You can learn more about that here: The Pathogens That Came In From The Cold
• Facemasks are better for reducing flu transmission than being unmasked
  • Importantly, masks do help, but are more important on an epidemiological level than personal (i.e. they protect society more than they protect the wearer), and they are impractical in many circumstances, and use of them is very low in most countries. So in other words: they’re good! But may be a lost cause at least for the time being. See also: Mythbusting The Mask Debate
• Vaccination is better for reducing flu transmission than being unvaccinated
  • Vaccines are considered the “gold standard” against COVID and many other infectious diseases, for their very high rate of efficacy, clear science, and at least moderately lasting effects (i.e., it’s not something like handwashing*, which must be redone very frequently). Since vaccines are not without their popular misunderstanders, we have written a little about that, here: Vaccine Mythbusting

So, those are important ones, but still not the only things we can do; consider for example: Beyond Supplements: The Real Immune-Boosters! ← most people don’t know these things and the huge difference they make!

Want to learn more?

For a deeper dive into immunity, here you go:

The 21-Day Immunity Plan – by Dr. Aseem Malhotra

Take care!