GEOFF BENNETT: Three years into the pandemic, cases, hospitalizations and deaths are all declining, but questions remain about new variants and whether some people may need a spring booster shot. William Brangham is here with an update on the state of COVID in the U.S. WILLIAM BRANGHAM: Geoff, it's worth noting good news when it occurs. And, on COVID, there is some. The U.S. avoided the worst of a winter surge, and weekly recorded deaths from this virus are the lowest they have been since the early weeks of the pandemic. But it is not all good news. More than 1,700 Americans still died last week because of COVID. And, for the elderly, immunocompromised and those still struggling with the little-understood long COVID, this pandemic is hardly in the rearview mirror. For another check-in on COVID, we're joined again by epidemiologist Katelyn Jetelina. She's at the University of Texas. And she writes the very informative Substack called Your Local Epidemiologist. Katelyn, great to have you back on the "NewsHour." What is your take on where we are in the trajectory of this pandemic? Deaths are down, as I mentioned, but there is this XBB variant that is -- subvariant, that is now dominant in this country. Where are we? KATELYN JETELINA, University of Texas Health Science Center: You know, it's a really good question. I think we're somewhere in between a full-blown emergency, like we saw in the beginning of 2020, and somewhere before an endemic. We're just not at a state where we know what this virus is going to do. And this virus is not being very predictable. Like you said, all metrics are nosediving right now. And that's good news. We expect that to happen with spring because of warmer weather, less holiday gatherings. But COVID continues to do its COVID thing and continues to mutate. It's what viruses do to survive. And we're paying specific attention to XBB offshoots, one in India and one in the U.K. That is causing a little disruption and some smaller waves. And so this does have the potential to disrupt a quiet spring in the U.S., but it's still too early to know for sure, given our complex immunity landscape. WILLIAM BRANGHAM: Speaking of that immunity landscape, it's been about six to seven months since the bivalent boosters became available, which is plenty of time for a lot of people to have lost some of their protection. You wrote about this today. Is there good evidence for a spring booster? KATELYN JETELINA: I think it depends on what you define as good evidence. It's really difficult for us to know how much each booster helps or does not help and incrementally, and get a grip on it prospectively. And so what we know for sure is that protection is robust for younger and healthier people, keeping them out of the hospital, which is great news. The concern is for immunocompromised and older adults with comorbidities. And this is because their immune systems are just not as strong. And it's being -- they're being pulled in multiple directions. And so this is a group where we really want to avoid infection in order to prevent hospitalization and death. And we know these antibodies, like you say, that prevent infection wane pretty quickly and only last about six months. WILLIAM BRANGHAM: And elderly Americans, 65 and older, those are increasingly the people who are still dying of COVID. Isn't that right? KATELYN JETELINA: That is correct. I think the last statistics was about 90 percent of deaths are among those over 65 years old; 96 percent of hospitalizations are among old adults, older adults, with at least one comorbidity, and because, again, their immune systems are just taxed. I think the good news is that very few people are in the hospital today who are up to date on vaccines. So, the vaccines are working. The essential question is, is this going to change in time? And what do we do proactively? WILLIAM BRANGHAM: I want to touch on long COVID, this still mysterious ailment that so many people are suffering from. What are we learning about who is getting it and why? KATELYN JETELINA: You're right. There's millions of Americans right now debilitated, out of work, suffering, with very few treatment options. We are starting to get a better grip on what causes COVID. It seems to be several factors, like, for example, a lingering virus or people harbor the virus in their tissue, which can create damage. I know that other people get long COVID driven by the immune system. Autoantibodies just start attacking the body itself. And then there's also just immune dysregulation, that, even if someone clears the virus, the immune system is off-balance, and so other dormant viruses reactivate and drive chronic symptoms. So, long COVID, we're learning, is really an umbrella term for several causes. And this is important to know because it'll allow us to understand how we can target treatments. WILLIAM BRANGHAM: And, lastly, in the few seconds we have left, on those treatments, there are some that show some promise on long COVID? KATELYN JETELINA: There are. There's about 300 clinical trials right now, and the results are starting to trickle in. For example, we see metformin, which is a very cheap drug. It reduces long COVID about 40 percent. Paxlovid reduces it a bit as well, maybe about 25 percent. So there is good news on the horizon. But we need more answers. WILLIAM BRANGHAM: Katelyn Jetelina, thank you so much for being here. KATELYN JETELINA: Thanks for having me.