At the three-year mark, coronavirus continues to evolve even as it produces significantly less severe illness.
Moderna and Pfizer are currently running trials for a fresh crop of booster vaccines, but it is unclear at the moment whether the nation will fall into an annual inoculation pattern similar to the one used with the flu or some other less-regular schedule.
Of course, the behavior of the SARS-CoV-2 virus in the real world will play a large role in dictating the response going forward as what was once a pandemic settles into an endemic state, always infecting enough people across the globe at any given moment to never truly disappear.
The true question is how this virus might or might not evolve to bring about a fresh surge of cases.
UC San Diego evolutionary biologist Joel Wertheim, whose work helped to trace the early emergence of the virus in China, discussed its likely path in the coming year and what would have to happen for it to go back to causing severe spikes in cases.
What follows is a lightly edited transcript of his answers:
Q: This winter has been very different from last in terms of coronavirus activity. Whether you look at wastewater or testing or total hospital patients, we have seen lower peaks and less strain on health care capacity despite new XBB Omicron subvariants circulating. What’s your read on why this has been the case?
A:Yes, it has been fortunately mild, and I think a lot of that can be attributed to the previous barrages we have experienced. You know, the viruses that are circulating now sure did a number in China, where they didn’t have as strong a vaccination coverage or previous infection.”
Q: You’re referencing China’s “zero COVID” policy which gave the population less natural immunity?
A: Yes. They didn’t vaccinate as many of the elderly as they had hoped, and their vaccine probably wasn’t as good as the one’s we have been using.
Q: So, what you’re saying is that the reason we have had smaller spikes on the epidemic curve this winter, compared to the last two winters, has a lot to do with the level of immunity already in the community?
A: Yes, from vaccine-induced immunity to maybe one or more previous infections, it means that when the new subvariants arrive here, they’re facing a much different picture than when they arrived in, say, China.
Q: For more than one year now, it has been Omicron subvariants that have continued to dominate. Why have we sort of settled into this sort of Omicron plateau and not seen another major extremely virulent and transmissible branch in the phylogenetic tree as we did with Delta and others?
A: That’s one of the big unanswered questions of SARs-CoV-2, where do new variants come from? With these subvariants that we have seen, first for Delta and now for Omicron, you see this incremental stepwise evolution of the virus as it is transmitted from person to person. But new variants such as the original Delta and Omicron, they have sort of appeared very different and fully formed and, because they’re very different, they’re able to sweep around the world very quickly. One of the leading theories on that phenomenon is that it comes from people who are persistently infected where the virus spends a lot of time adapting to an individual.
Q: Is this often in people with compromised or weak immune systems who just can’t fully clear the virus after becoming infected?
A: That might be a piece of it, but I’m not convinced that it has to be in someone who’s immunocompromised. I think that healthy people may be able to just be persistently infected and what happens is you have this sort of blast from the past, you know, from deep within the viral phylogenetic tree just appearing after all of this adaptation, and all of these mutations, and then it’s just suddenly back on the scene, more efficient at infecting people and getting around pre-existing immunity. There are some theories that maybe we could be seeing a sort of reverse zoonosis with the virus moving back into animals, continuing to evolve, and then jumping back into humans. I favor the theory that new major variants come from persistently infected people but, again, this is really an unknown in terms of COVID science.
Q: Do you see signs that we’re in for another nasty main coronavirus variant emerging in the next year or two?
A: I would never underestimate a circulating virus.
Q: At the end of the day, this is just natural selection on a massive scale, right?
A: Exactly. The more people that get infected, the more opportunities we have for something new to appear. It could take months, and it could take years, but I imagine we will see another large wave at some point in the future. We’re certainly in a very different place at three years than we were at the beginning. Not every year is going to be a bad year, but some certainly will be as SARS-CoV-2 is endemic in humans now and it’s not going anywhere.
Q: Would you say we’re in sort of a flu pattern to some degree where we can expect there to be some background level of infection that spikes in some years and is flat in others?
A: Well, we don’t have nearly as much experience with this virus as we do with the flu. So we don’t know what the cycles are going to be yet. But, yes, it’s similar in that some flu years are really mild and some are much, much worse. As this virus continues to adapt to us, some years it will be better at causing illness and infecting people, and other years, less so.