Weekend Long Reads: Bitterness Isn't All Bad

by Kevin Schofield

This weekend's "long read" is a collection of three shorter reads: a trio of research papers on COVID-19. The virus — and the vaccines — have now been around long enough that the medical research community has large and diverse enough data sets to start to really understand this virus. Along the way, researchers are discovering some fascinating and mystifying things.

The first paper starts to answer the question as to how long we can expect immunity from COVID-19 to last for someone who contracted the virus and recovered. Previous studies had found that the quantity of COVID-19-fighting antibodies in the bloodstream dropped off considerably in the first few months after a patient recovers, causing the medical community to worry that immunity might be very short-lived (as is the case with many other coronaviruses). This new study found that too, but it sampled again 11 months after recovery — since there is now a large cohort of people who are more than 11 months post-recovery — and found that the drop in antibodies slowed considerably after four months. This is consistent with doctors' understanding of how our long-term immune system works: As we're fighting an infection and in the few months that follow, plasma cells in our bloodstream generate large quantities of antibodies that target the virus. But after that, long-lived plasma cells settle into our bone marrow and generate a lower, steady level of antibodies that can last for several months or years. In the study, the researchers took bone marrow samples from patients and found that, indeed, the patients had long-lived plasma cells protecting them from a COVID-19 reinfection. The researchers also found that our immune system's second line of defense against a reinfection, so-called "memory B cells," were also present several months after a patient recovers. Together this is strong evidence that we humans can generate a strong immunity to COVID-19, after being infected, for at least a year — and perhaps for years.

SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans

The second report is from the CDC's researchers who are studying "breakthrough" infections: People who contract COVID-19 after becoming fully vaccinated. In the first four months of 2021, there were 10,262 breakthrough cases reported in 46 U.S. states and territories. That may sound like a lot, but as of April 30, there were 101 million persons vaccinated in the United States. This is a case of the "law of large numbers": Even when something occurs extremely rarely, if the sample size is large enough then it will eventually happen. And let's not forget: In early January, the United States was seeing about 250,000 new COVID-19 cases per day; by April 30, that had dropped to about 50,000 cases. Over that four-month period there were 10 million new cases in unvaccinated Americans, while there were only 10,000 cases in the vaccinated ones.

The United States is still seeing more than 20,000 new COVID-19 cases every day; that's twice as many cases in a single day than all of the breakthrough cases in the first four months of the year. The COVID-19 vaccines are not perfect, but they are very effective, and the number of breakthrough cases seen so far — even with new variants of the virus in circulation — are even more evidence that vaccinations are working as advertised.

COVID-19 Vaccine Breakthrough Infections Reported to CDC — United States, January 1—April 30, 2021

And now we get to the weird paper. It has been well-documented that humans have a range of sensitivity to bitter tastes, from "nontasters" who experience low or no bitter tastes through "supertasters" who experience greater intensity of bitter tastes. Scientists have not only identified the taste receptors that allow us to taste bitterness, but also the genetic variations in those receptors that correspond to our range in ability to taste bitterness. About 25% of the human population are supertasters, 25% are nontasters, and 50% are in the middle.

What does this have to do with COVID-19? A lot, it turns out. A study of 1,935 patients and health care workers with exposure to the COVID-19 virus, who fit the expected distribution of nontasters/tasters/supertasters, were tracked for possible COVID-19 infection. Nontasters were far more likely to test positive for COVID-19, to be hospitalized for treatment, and to be symptomatic for a longer duration. The numbers are striking: 13.7% of all the study participants tested positive: 55% of the nontasters, 29% of the tasters, and only 5.6% of the supertasters. Of the 55 people hospitalized, 47 were nontasters and none were supertasters. Nontasters had symptoms an average of 23.7 days; supertasters had symptoms for 5 days.

The researchers think they know why this is happening, too. It turns out that we humans have bitterness taste receptors in our nasal passages as well as our mouths; the ones in the nose aren't wired up to give us taste sensations, but when activated, they release nitric oxide as one more part of our body's immune response. The nitric oxide fouls up the ability of spike proteins on foreign bodies such as the coronavirus to unlock and then infect our cells. And since we know that the virus most often enters our body through cells in our nose, this turns out to be a pretty potent defense. According to the paper, supertasters appear to be the majority of asymptomatic or noninfected COVID-19 carriers; nontasters are the ones with the most severe symptoms; and the 50% in the middle account for people who incur a wide range of symptoms but eventually recover.

This is definitely a research study that should be replicated before we take it for gospel, but it's a super interesting result. If it proves out, it could be a critical tool for predicting not only who might contract COVID-19, but who is most likely to end up hospitalized. That could save many lives.

Association Between Bitter Taste Receptor Phenotype and Clinical Outcomes Among Patients With COVID-19

📸 Featured Image: Photo by Alex Guillaume on Unsplash.