Oregon Health & Science University’s latest forecast suggests COVID-19 hospitalizations will stay at extremely high levels until early October. Peter Graven, lead data scientist at OHSU, joins us with details.
This transcript was created by a computer and edited by a volunteer.
Dave Miller: This is Think Out Loud on OPB, I’m Dave Miller. We start today once again with Peter Graven. He’s the Director of the Office of Advanced Analytics and the Lead Data Scientist at OHSU. Throughout the pandemic, his modeling about COVID-19 case rates and hospitalizations has been singled out by policymakers as one of their reasons for imposing or reimposing various public health measures, like mask mandates and restrictions on public life. Now that the surge in cases driven by the delta variant seems to be slowing down, we thought we’d check in with Dr. Graven to get a sense for what he is expecting next. Peter Graven, welcome back.
Peter Graven: It’s a pleasure to be here.
Miller: Is it safe to say that the delta surge is easing?
Graven: You know, the forecasting has been pretty pretty accurate here. We did see a peak that arrived around September 1st, and we’re seeing a decline in the primary metric that I look at, which is that hospital census, the number of people in hospital beds across the state of Oregon. We are seeing a decline in that level. Now, that still means there’s a lot of transmissions happening to even maintain that level of census, but it is certainly not getting worse and it appears to be declining.
Miller: So what’s your sense for what hospital capacity will look like in the coming weeks?
Graven: Well we are hoping to see some improvement throughout October. Hopefully towards the end of November we would expect to get to lower levels that we’d seen prior to the surge. But in the meantime what we’re really looking at is a whole bunch of beds that have had COVID patients that haven’t had other types of patients there. And because of that, a lot of procedures have been postponed or delayed. And a lot of other care has been kind of put to the side. And so we know that there’s a lot of pent up demand for what’s needed in our hospital. They’ve all been full. If you ask them, they’re going to feel like they haven’t felt much relief yet. But it’s getting better slowly.
Miller: And is it fair to say that we’re still then, and for the coming weeks it’s likely that we’re still going to be at a higher rate of hospitalizations than we have been at any other point in Oregon in the pandemic?
Graven: That’s right. I don’t see us coming down to even the previous peak for another few weeks at least. And that was from the fall and winter surge. And then another few weeks after that until we get down to the spring surge, which was another high level of census. And really what that means is, when the census is coming down, it means that there’s new admissions happening every day and there’s people being discharged every day. And it’s just that you’re having a little bit more discharge than admission. Unfortunately, some of those discharges because people are dying as well, and that’s, and that’s part of the equation.
Miller: What is responsible, if you can identify it, for the slight drop that you are seeing?
Graven: I relate it to two main things. One is that we did take some real actions here in the state to slow down transmission. I know none of us wanted to, but when Delta hit, it turned out we weren’t at the vaccination level we needed to be, and we needed to put our masks back on because there’s just too many susceptible people.
So, the mask policy, we did see a good impact from that. Our mask rate went up, and we also got the corresponding decrease in transmission. So I think that was effective.
Miller: If I could stop you, I’m just curious how you are able to make that causal link. I mean obviously, the mask mandate went into effect, and I suppose that anecdotally or maybe with data, you’re able to know or approximate how many Oregonians are following it. But how do you then say that to some extent the drop in new infections is directly tied to Oregonians wearing masks?
Graven: Doing a good causal study is hard. And the reality is you’re gonna want to do comparisons across lots of states. I’m kind of doing that casually, in the sense of saying Oregon peaked earlier than we would have expected and we saw other states peak given how we’re increasing. I see that at the same time that the mask wearing rate got up to over 80%.
Miller In other words, there were other states that didn’t impose mask mandates and their case rates continued to climb. So that’s a marker of, of the mask mandate working.
Graven: Exactly. But your question is right, which is, to really tie these together directly requires more data analysis that will take place later, when we have a longer string of data to look at. But in the meantime, I’m seeing all the signs that it was helping. But masks aren’t perfect either. And so there’s still transmissions, in particular amongst people who are not wearing masks and who were unvaccinated. And that’s part of it, even if you get to an 80 or 85% mask wearing rate, if the 15% that aren’t are unvaccinated, you’re still going to have some transmissions. And we’re still seeing that today.
Miller: Is it possible to see among that population you’re talking about there, people who aren’t vaccinated and who are against wearing masks, how close are we to the virus running out of people to infect? Because that population has gotten infected?
Graven: My latest modeling shows that about 25% of people are susceptible. What that number is looking at is both people have been previously infected and people have been vaccinated in the overlap between those two. And with that, we’re down to less than a quarter of people are still susceptible. Remembering that this also subtracting out people who, even though you got vaccinated, I have to take out 5% or so because the efficacy of the vaccine may not actually prevent the transmission. And so when we look at it that way, we are at around 25%. The more recent estimates of R0, which kind of dictates how fast it is and the herd level we have to get to, means we have to get down to about 15%. And for those who are listening closely, last time I said it down to about 10%. So that’s slightly higher than before. And we’re gonna be slowing down as we get into that, and that’s what we’re seeing now. We have been infecting a lot of people over the last two months. And that does make it a little trickier for the virus to spread.
Miller: Can you remind us what the R0 is?
Graven: Yes, R0 is the metric that is used to describe how quickly a virus can spread. And it’s really a number that can be thought of as: for every person that’s infected, how many people do they give it to during the time that they’re infectious? And so if the R0 is 3, that means that each person getting infected will infect three others. The current estimate for the Delta variant is about 6.5. So that means on average you’re gonna infect 6.5 people, assuming you don’t take any precautions.
Miller: I just want to go back to one thing you said earlier because it does seem like it’s an important piece here. If I understand correctly as you’re doing your modeling, one of the pieces of data that you are including is the percentage of Oregonians who have gotten infected. That is a key piece of this. Not just vaccinations which we pay so much attention to because it’s voluntary and preferable, but also people who have been naturally infected.
Graven: That’s right. Those previous infections, we have an estimate of how many they are based on how many people showed up to the hospital. For every person in the hospital, we know that there is going to be a certain number of infections that basically cause that to transpire. And we’re estimating, so we don’t have a great account of exactly who is infected or not, and I think listeners can understand that. But in terms of the gross population of Oregon, we can make some estimates there, and that does help us to understand how the virus can slow down, as folks are getting infected or hopefully vaccinated.
Miller: I mentioned in my introduction that your modeling has, not alone, but to some extent has led state policymakers to say, “We don’t want to do this, but it’s time for us to re-impose a mask mandate,” for example. I’m curious about the flip side of that. What does your modelling suggest in terms of when it would be appropriate for the state to drop the reimposed mask mandate in public spaces?
Graven: Well, I think the reality has been, we’ve gone through many waves here. And it’s no surprise that it’s a lot easier to take on some of these precautions when you see that things will get better at some point in the future. There’s been forecasts out there that would show that it would just get worse forever and ever. And of course that’s not realistic. And so I do think the forecast helps us to understand we’re going to do a thing for a period of time, and then yes, there is hope at the end, that we’ll be able to lighten up on these. And the metric I would use of course is our hospital census there again. We just don’t have room for other people getting sick right now, so we’re not in that space. Right now, there’s a pent up demand for people who need care. And we need to be able to deliver that. And so we just don’t have room for us to kind of take on more risk.
But there will be a time. My guess is as we move through the fall here, particularly as we move back indoors, which we have to be extremely careful about, if we’re not seeing a lot more transmission, then we know some of that immunity is holding. If people are getting their boosters, and if we’re able to vaccinate kids 5 to 11, I think we should start seeing the benefits of all that. And by January, I think we’ll have good information about what things can be changed.
Miller: So as you noted, one of the pieces there in the possibility of your recommending the mask mandate be lifted by January is children ages 5-11 becoming eligible for the vaccine, potentially in late October maybe early November. We’ve heard conflicting timelines and there are still a lot of things we don’t know. What difference do you think that would make in terms of the modeling that you’re paying attention to?
Graven: In terms of the modeling, kids aren’t a big, huge source of admissions to our hospital space. We’ve luckily had enough space for the admissions we’ve had from children. They do contribute to the transmission, but more generally, I think they contribute to our sense of vulnerability. If we know we have a group of people that can’t be protected by a vaccine, it’s really hard to say we’re fine with letting this risk play out. And I think as people feel like people have had a chance to protect themselves and the people around them, then the mood may change to a place where some of that risk, we’re more willing to accept.
Miller: I’m looking at a window right now, looking at the rainfall, which is obviously welcome for a lot of reasons. But in terms of COVID precautions, it’s different than thinking about rain, putting out wildfires. We’re about to enter the second cold, wet, rainy season of this pandemic. How do you measure fatigue when it comes to people who are not vaccine skeptics, who are totally on board with wearing masks and following public health guidelines, but who are also just getting so tired of this, and are maybe thinking about socializing inside once again, as opposed to being outside. How do you measure fatigue?
Graven: Fatigue is a real thing, and that’s been a pattern I’ve seen throughout the pandemic here and in Oregon in particular. We’re able to hold onto strict policies for some period of time, and then after a while, usually when things start looking better, we say maybe I can take a break. That’s been our pattern. I expect that to continue. We’re humans, that’s what we’ve been doing, and I expect us to do that again. Now the benefit this time is when we do start to relax, we have a much higher vaccinated population. And unfortunately, we also have a higher previously infected population. But both of those are going to help us, so that if we do take steps in that space, we shouldn’t expect as large of a surge as we did. For instance, last year, you may remember we had a huge surge that began right when everybody went back indoors. And so I’m hoping we can avoid that.
Miller: I’ve heard various Greek letters being used to describe some of the post Delta variants that have popped up on public health radar. But so far it seems like nothing has replaced Delta on the global stage as the chief variant of concern. Is that what it looks like from a modeler’s perspective? Or is there something else out there that seems like the key variant to worry about?
Graven: No, it’s still Delta. And so far, we haven’t seen the signs that are problematic of a virus that is growing very quickly in a place that is similar to ours in terms of vaccination levels or previous infection levels. While that’s not happening right now, it is quite likely that we will have a day where we open up the paper to a new variant, where our previous immunity may not provide the same kind of protection. I’m not looking forward to that day, but I’m going to be prepared to model it. In the meantime, we’re gonna need to get used to probably getting vaccinated on a regular basis. Hopefully it’s just annually, like you would with a flu shot. But the time span may change as well.
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