Viruses evolve and weaken over time — what does that mean for the coronavirus?
AYESHA RASCOE, HOST:
It's too soon to say how the coronavirus, which is the virus that causes COVID-19, will evolve over time. But other viruses that once started strong have waned over time. That's one theory for the common cold. Here to explain why and whether the omicron variant fits into that pattern is Jennie Lavine. She's the senior computational biologist at biotech company Karius. Jennie Lavine, welcome to the show.
JENNIE LAVINE: Hi Ayesha. Thank you so much for having me this morning.
RASCOE: So one theory that we've heard a lot about recently is that viruses tend to mutate to become weaker over time. Is that right? And if so, why?
LAVINE: Yeah, the currency for viruses is they want to be as transmissible as possible. From their sort of evolutionary perspective, they don't really care whether or not they're causing disease in you as long as you're going to transmit it. So if a virus can make more particles, it's probably going to do better. But if at some point, it's making so many particles, you know, replicating so much inside you that it's making you super, super sick, at that point, you might not go out. You might not go to a party. You might not go to work. Worst-case scenario - you might die. That can lead to this relationship between how severe the disease is and how transmissible it is such that when a disease gets too severe, it's not good for the virus anymore.
RASCOE: And so tell us about the history of the common cold. It killed people. Like, when was that? And why did it evolve the way it does today, where it's just the common cold?
LAVINE: Yeah, yeah, so back in the late 1800s, there was a pandemic which was termed at the time the Russian flu. Well, people have gone back now, and there's sort of two lines of evidence that suggest it's possible that that was actually the origin of one of the four endemic coronaviruses. So today it's called Human Coronavirus OC43. You and I and everybody listening to this show has been infected with OC43. The Russian flu killed, like, millions of people. It was huge, huge, huge. And the symptoms were surprisingly similar to what we are seeing today with SARS-CoV-2. It included things like neurological symptoms, things that are not necessarily associated with what we think of as the flu, right? It included loss of sense of smell and taste at times. It's a pretty interesting hypothesis.
RASCOE: This pattern that you're describing - it doesn't apply to all viruses, like HIV. And then there's polio. Why haven't those viruses become less potent?
LAVINE: I mean, some of it is evolution is unpredictable. It's about random changes that occur. And so we can't fully, like, predict what is going to happen evolutionarily. But one of the key aspects is, how is the virus transmitted? If the virus is transmitted person to person like respiratory viruses in general, including SARS-CoV-2 - you need that person to be active and going out and seeing other people. Polio, on the other hand, can survive in the environment to some degree. And this means that it can get transmitted even when you are sick.
RASCOE: That being the case, where does omicron fit into this pattern? Like, is it more contagious because it's weaker or - and not killing its host as quickly?
LAVINE: Omicron is really way, way better at transmitting in this current human population than, for example, delta was in the population that it was transmitting in - not knocking delta here, but I'm just saying omicron is fantastic at transmitting in this population. And one of the characteristics of omicron, it's clear, is that it's very good at evading neutralizing immunity. It's good at evading the antibodies that come in and sort of prevent it from even replicating. What it doesn't evade is a lot of the kind of broader T-cell-based immunity that often will make - you'll still get infected, but the infection will be shorter, and you'll - because you'll clear it with this T-cell-based immunity.
So that's all to say omicron is clearly more mild in terms of the infection fatality ratio, in terms of the hospitalization rate. How much of that is because the virus has evolved to be milder in all the ways we were just talking about in terms of this relationship between transmission and virulence? Possibly - also totally possible it's about the same amount of virulence, but our population has so much more immunity that we don't get nearly as sick. And this is true even in places where the virus has transmitted so much, unfortunately, in the past that there is a lot of population-level immunity even without high vaccination rates.
RASCOE: That was Jennie Lavine, senior computational biologist at Karius. Thank you so much for joining us.
LAVINE: My pleasure. Thanks. Transcript provided by NPR, Copyright NPR.