We’re in the midst of yet another COVID-19 wave, while also approaching the season for flu, RSV, and other pathogens that typically spread in the colder months. And we’re doing so with more barriers to common safety measures than any winter since the pandemic started, as the Trump administration restricts vaccine access amid other threats to public health.
To offer guidance on finding and interpreting infectious disease data during these confusing times, managing editor Betsy Ladyzhets talked to Caitlin Rivers, an epidemiologist at Johns Hopkins University’s Bloomberg School of Public Health and author of the popular newsletter, Force of Infection, as well as the recent book Crisis Averted: The Hidden Science of Fighting Outbreaks. Rivers’ newsletter provides regular updates about trends in COVID-19, flu, RSV, and other common infectious diseases, along with commentary on public health issues.
Rivers discussed which data sources she relies on for her trend updates, interpreting data for day-to-day decisions, questions she still has about COVID-19 patterns, how the Centers for Disease Control and Prevention (CDC)’s data pages could better acknowledge Long COVID, ongoing bird flu concerns, and more. This interview has been lightly edited and condensed for clarity.
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RSSBetsy Ladyzhets: So I wanted to start by asking a more straightforward question: What data sources do you use as you’re writing your updates?
Caitlin Rivers: The main data sources I use are the CDC’s data sources. For COVID-19, I use wastewater, emergency department visits, and test positivity as my three primary indicators. And I have similar sources as well that I use for influenza and RSV, but I also have backup sources because sometimes [a CDC page] isn’t updated on time, or there’s a gap in availability. And so I have a few backup options for all of the pathogens that I surveil, but those are the big three.
BL: Makes sense. I know WastewaterSCAN is a big one for the wastewater data. Do you look at that as well?
CR: Yeah, I use WastewaterSCAN and Biobot, but my first preference is to use the CDC data, because they aggregate all of the wastewater providers [including data from WWSCAN and state and local health departments] and so they have better coverage. But when their source is not available, then I go directly to WastewaterSCAN.
I also really like that WastewaterSCAN includes surveillance for a lot of different pathogens that they don’t send to CDC, or at least are not publicly available from the CDC side. So if I’m checking in on EVD68 [an enterovirus that causes common cold symptoms], for example, or Mpox — it is a great resource for a whole bunch of pathogens. So I appreciate that about them as a source.
BL: They’re so comprehensive, it’s great. What do you see as some of the advantages and disadvantages of some of those different types of data that you just mentioned?
CR: Wastewater is one of the leading indicators, and it’s really good for showing trends, particularly at times of inflection. So when things have been quiet and they’re starting to pick up — or they’ve been high and they’re starting to come back down — I really appreciate wastewater for those periods. But it’s a little bit hard to understand on a one-to-one basis what wastewater means exactly. And so that’s why I don’t use it exclusively. I use it in combination with clinical indicators.
After wastewater, emergency department [ED] visits are my favorite indicator, because it’s comparable across pathogens and across the time of the year. So you can have a really good sense of how COVID is looking compared to flu, or how this season is looking compared to last season. And that’s not as easy to do with wastewater. And then the third that I look at … is test positivity. And again, that’s a leading indicator, and it’s good at showing times of change. I use it to fill out my understanding about those periods of time.
BL: That was something else I wanted to ask about, is those periods of change. I noticed you wrote in your update last weekend [on August 31] that trying to identify when a season is starting or when a wave is starting, and then also when it’s peaking, is really difficult. I was wondering if you could talk more about why that is so difficult, and also how you try and think about doing that.
CR: Yeah, seasonal onset and peak week are the two hardest to forecast or to analyze, in my opinion, because they’re times of change. [In comparison] it’s really easy, if it’s early in December and flu has been going up, and I can feel pretty confident it’s going to be going up again next week. But when you’re really looking at those times of change, the data are lagged, and so you’re having to understand, “Okay, a week ago it was this, what does that mean for now?” And often the indicators are subtle, so you’ll see, a slight slowdown, and maybe you see ED visits dropping. But is that just a blip, or is it going to go back up again next week? It’s subtle.
And it’s important. That’s the other reason it’s difficult, because those are two points of interest that people care about: when is a new wave starting, and have we passed peak? The easiest thing to do is to wait and see, but it’s not helpful after a while. If you wait three weeks to say, “Oh, peak week was three weeks ago,” that’s not going to be as helpful for people who are really trying to use this information to navigate.
So I do try to make the calls, but I also try to be transparent about what I’m seeing. [I’m] really explaining, “Here’s why I think this,” and then conveying uncertainty when I feel it, so that people can make their own judgments or get a sense of how to interpret the information I’m offering
BL: I wonder if part of the challenge, too, is that, especially the peak weeks often correspond with holidays when we get extra data delays. We just passed Labor Day weekend, and often, in the winter, [peaks happen around] Christmas and New Year’s.
CR: Absolutely, it’s such a pain. It’s always around the Christmas holidays or the winter holidays, … and there’s often no updates that week, or they’re delayed. It is definitely super frustrating. This past winter, during the presidential transition, when President Trump was inaugurated, there [were] no data updates for a week.
BL: Or not full data updates? I think the wastewater [data were] updated … but not some of the other stuff. Or some metrics were updated on some dashboards, but not others.
CR: It wasn’t normal. It was in the height of flu season. We had kind of passed peak, but I was still keeping really careful watch. And so I went to all 50 state [health department] websites to look for flu data, and I found that there was actually a rebound. We were having a second peak. If I hadn’t put in the effort to go site by site, then we would have missed [this news] or it would have been delayed. [I was] able to share the information of something really important happening.
If I hadn’t put in the effort to go site by site, then we would have missed [this news] or it would have been delayed.
Caitlin Rivers
BL: How do you find that people are interpreting and using these data, or using the updates that you write? I’m curious what kind of feedback you get from your readers on this stuff.
CR: I have a general readership, so [it includes] all sorts of people. But the two largest constituencies, I think, are healthcare workers who use the information in their practice — I have a lot of pediatricians, for example, who keep on top of trends so that they can take better care of the kiddos —and the second largest constituency is people who are medically vulnerable. They’re immunocompromised, they’re older adults, they have a health condition, or they have a loved one that is experiencing those challenges, and they use that information to make decisions about their lives, like whether to attend a gathering, or whether they’re going to mask if they haven’t been doing so. Really figuring out ways to keep themselves safe.
BL: Along those lines, a question that I get sometimes — particularly about wastewater data, but I think it also applies to the other types of data — is interpreting from the broader geographic areas that we actually have data for to your more specific circumstances. Wastewater surveillance is not happening everywhere, so sometimes it’s not in your specific county or your city, but maybe it’s like, in one that’s a couple hours’ drive from you, or elsewhere in your state. Or with emergency department visits, those are state by state, or test positivity is region by region.
What advice would you have for people in looking at those numbers that are maybe a little bit of a broader region, and then thinking about more individual decision-making?
CR: It’s true that some indicators are really only available at the regional level. … I think state data tends to be pretty reliable in terms of making qualitative decisions about your everyday life, and so I feel comfortable using state data even for local happenstance.
But there are a few other tidbits of information that you can use to fill in the blanks. Urban areas tend to lead in terms of new outbreaks or new changes in disease activities. So if you’re urban, maybe you’re a little bit more on the cautious side in terms of interpreting state data. Rural areas tend to experience [changes] later. And then children are always first. If you have children in your life, I would again, lean a little bit more on the cautious side when looking at the data, because they’re going to be hit first.
BL: That makes sense. Are there things that you personally do, if you’re comfortable talking about it, how you might adjust yourself based on some of these data points?
CR: I wear a mask when incidence is high, when there’s a lot going around. I always, always, always wear a mask when traveling, regardless [of disease levels], because [when traveling] you come in contact with so many people from all over the world.
And actually, during the Omicron wave back in 2021 [through early 2022], I kept my kids home from school past the end of winter break because I just knew that they were going to get sick, and I didn’t want that. So I have made those kinds of decisions for my family. But I know that people who are dealing with more health-wise have to make those kinds of decisions all the time, and there it’s a much more challenging position.
BL: It’s interesting, I’ve heard from readers who say the COVID updates are not so helpful anymore because they just assume [disease spread is] high all the time and they are always masking. But I think so much of that is an individual call that people make, and is tough when we have less public access to [data] than we maybe did a few years ago.
CR: There’s a lot of decision fatigue that I hear about, too, like constantly having to make adjustments. I do hear from readers who have just decided, “I would rather take that decision off the table and feel confident, then kind of go on and off.” But other people do like to have that flexibility. So it has turned out to be very individual.
BL: Another thing I wanted to ask about with wastewater data is, there are some folks on social media, and there’s also the Pandemic Mitigation Collaborative, is the name of one dashboard, that model SARS-CoV-2 infections from wastewater surveillance numbers. Personally, I don’t cite them, because I feel like that type of modeling is very difficult, and there are a lot of uncertainties with it. I’m curious if that’s something you ever look at or cite, or what you would advise about looking at those sorts of updates.
CR: Yeah, it’s not something that I look at, either. This is called “burden of disease” in epidemiology, and it’s pretty well-established for influenza: if you see so many hospitalizations, what does that imply about the number of infections in communities? But that hasn’t been well-established for COVID, and I wouldn’t want to just use wastewater to make that analysis. It would have to be a constellation of indicators, and so that’s not something that I rely upon personally.
BL: That makes sense. I know they [the CDC] do burden estimates during the winter season for flu and also for COVID, but the COVID one is such a wide range … We’re still figuring out how to do that.
CR: [Figuring out] what the multipliers are? Yeah, that’s the hard part.
(Editor’s note: In the CDC’s 2024-25 burden estimates, flu actually has a wider range than COVID-19; that winter saw an unusually severe flu season.)
BL: Are there other differences, or other ways that you think about COVID differently as compared to other pathogens like flu and RSV that have been around for much longer, and where we understand the seasonality better?
CR: The big difference is that COVID peaks twice a year. There are other pathogens that peak twice a year, but they’re not major respiratory pathogens, and so that is definitely a departure from flu and RSV that [peak once a year]. But there are plenty of similarities. They all hit children first, and young children and older people are at highest risk of severe illness.
BL: I guess it’ll be interesting to see whether we continue to get COVID [both] in the summer and the winter as it’s been in the last few years, or if that changes over time.
CR: I think so. I think we’re gonna see twice a year permanently, but we’ll see.
The big difference is that COVID peaks twice a year. There are other pathogens that peak twice a year, but they’re not major respiratory pathogens.
Caitlin Rivers
BL: Another about burden of disease: I sometimes put in my own updates, given that I’m writing for a more Long COVID-focused audience, that dashboards like the CDC’s, they often don’t include long-term impacts of infections. Not just Long COVID, but we also know that things like myalgic encephalomyelitis, can follow the flu, in perhaps smaller numbers. I’m curious how you think about those kinds of long-term outcomes. We know they’re very hard to track, but I think for many people, that’s an important motivator for trying to avoid infections as well.
CR: They are hard to track, but it’s so important. The basis of epidemiology is getting a good accounting of the burden and the impact of disease, and it doesn’t stop when the acute infection is over. You have to look at the long-term consequences, or the life cycle, [the disease’s impact] across the lifespan. I do think those kinds of analyses, or bringing that kind of lens to the data, is super important, because those are consequences that real people experience and live with.
BL: As we go forward and we continue to see these kinds of outcomes, what are some ways that the CDC or other public health organizations might better incorporate that [long-term outcomes]? People in the Long COVID community, especially those who have started having symptoms more recently, often talk about feeling like they didn’t know, or they didn’t really have a warning [that chronic illness could happen to them]. So I think [about], how do we better incorporate this into public health communications?
CR: I have an epidemiological lens, so I’m sure that there are colleagues in other fields who would have their own ideas about how to share from a communications perspective or health behavior perspective. But on the CDC’s COVID website, for example, they have data aggregated about MIS-C, the multi-system inflammatory disease that affects children. I don’t think there’s anything like that for Long COVID.
And so even just bringing together the data and making it available at the places where people are already looking for information about COVID, I think would be helpful for helping people to understand that it is a problem, and also the magnitude of the problem.
BL: The CDC does have some Long COVID data, but it’s in different locations.
CR: It’s separate, yeah. Zooming out a little bit, that’s always been a problem, from my perspective, with the way that CDC shares respiratory virus information. It’s changed in the last year or so, but historically, you had to go to the flu page, and then you went to the RSV page, and then you went to whatever. And not only do you have to come to the realization that you need to do all that Googling — it’s a lot of steps. It’s a lot for people to navigate themselves.
I think the more that we can push out information and reach people where they are, like their inboxes, in the case of my newsletter, the more likely it is that we make it easy to digest and accessible.
BL: Yeah. [The CDC now has] that “respiratory virus page” that has COVID and flu and RSV, right?
CR: Yes, that’s brand new. That’s definitely started since I started my newsletter. I think it’s a great development.
(Editor’s note: While the CDC continues to characterize SARS-CoV-2 as a “respiratory virus,” there is extensive evidence that it impacts every organ system.)
BL: Are there other changes that you’ve seen or ways that communications have sort of changed in the last few years? The public health emergency for COVID ended a couple of years ago, so that was obviously a big shift.
CR: The end of the public health emergency meant the end of several different data sources, which I think was a shame. It did become a little bit harder to have a comprehensive understanding of what’s happening with COVID.
People often ask me if the current administration means that the data has degraded or is no longer reliable, and I actually haven’t seen that. I’ve found that it is still updated regularly and it’s still high quality, so I continue to have confidence in it. But what has changed, and has come and gone over the years, is effort put into public communications. Are there CDC press conferences? Is there a social media presence that is aimed at the regular American? Are there easy-to-digest resources? … Right now, I’m seeing a pullback in that kind of information.
The end of the public health emergency meant the end of several different data sources, which I think was a shame. It did become a little bit harder to have a comprehensive understanding of what’s happening with COVID.
Caitlin Rivers
BL: I also wanted to ask you about bird flu, which has been less in the news recently, but we still have people asking about this. How are you following data on that at the moment, and [do you have] any recommendations for people who are interested in keeping up with it? We also published an article recently focused on farm workers being at higher risk, and ways to help them, like donating masks or trying to get information out.
CR: The first thing to know is that it’s seasonal. We haven’t been hearing about H5N1 so much in the news recently, and that’s because it’s out of season. Peak season in birds tends to be late winter, early spring. And of course, the more birds that are possibly infected, that are traveling the flyways, the more opportunities there are to spill over into other animals. And so I expect it will come back and be back in the news come wintertime.
It’s true that farm workers, veterinarians, people who are in contact with animals, particularly dairy cows, are at higher risk of infection. [H5N1] remains rare overall, but those are the populations that we worry about most. Masking, hygiene, surveilling, and doing disease control in animals — those are all going to be the strategies that help to reduce risk. That’s the current situation,
Longer-term — I’m an epidemiologist that specializes in high-consequence events, and the big fear is that H5N1 mutates to become easily spread between humans. Right now, it is not easily spread between humans, but flu loves to change. Can’t trust it for a second. The big fear is that it gains that ability, and so that’s why it’s something we [epidemiologists are] watching so closely, even though it’s a rare illness right now,
BL: I know last winter, because there was a higher than average flu season, there was the big concern about, maybe, infections coinciding between seasonal flu and H5N1. I imagine that will be a concern again this year, once we get into flu season again.
CR: Yeah, co-infection is the big risk, [both] in animals and in humans. One question I get a lot is, “How do we know that H5N1 isn’t secretly circulating during flu season? How can we be confident that the cough and the sore throat isn’t H5N1?”
I’m actually not that worried about that, because there’s a lot of genomic surveillance that goes on for influenza, and it types and subtypes it. We have a pretty good look at the kinds of subtypes of influenza that are circulating.
BL: And that happens for COVID, too. I actually noticed the CDC just started doing variant updates again for COVID with an updated schedule [once a month as opposed to every two weeks]. So that was good to see. I was worried that they would just stop.
CR: I think that program is pretty well supported. There’s a lot of recognition that genomic surveillance is important for COVID, and I think it’s important for the interested average person, too, because you can get a sense of how well — maybe I’m overestimating how curious people are, as an epidemiologist —
BL: Maybe our readers, more so than the average [person].
CR: You can kind of get a look at whether what’s going around matches what’s in the vaccine. And so I always find that interesting to do that comparison.
BL: Yeah, I’m curious to what extent you think about this — [it seems] variants sometimes are related to a new wave, where you see something new coming in and becoming a dominant variant, outcompeting others. And then maybe that contributes [to a wave], along with the seasonal behavior. I think people were saying last summer, that that was why last summer[‘s COVID-19 wave] appeared to be higher than average.
CR: I think there’s three main factors that drive waves. I think that new variants is one of them, but there’s two others. The second one is waning immunity, and so we know that both infection and vaccination confer fairly short-lived immunity for COVID, and so people become susceptible again fairly quickly. And then the third is this seasonal component, which is not fully understood. Sometimes you’ll hear, “Oh, people are inside more in the summer, and then they’re inside more in winter.” That doesn’t quite hold water for me, like, I’m inside almost all the time.
BL: [There’s something about] different parts [of the country]? Like, if you’re in the south, you’re inside more in the summer? I also don’t know — we’re not fully there yet with being able to explain it.
CR: And if that were a major driver, why don’t we see that for influenza? I don’t know. I don’t think we fully understand the drivers behind seasonality [with COVID-19], but there is clearly something going on there.
BL: You mentioned vaccines, which I wanted to ask about, too, of course. There’s so much uncertainty and concern about the COVID vaccines for this fall. How are you following the information on this? What are some sources that you would recommend, and advice for people who are trying to get access to vaccines at the moment?
CR: There’s so much cacophony around the vaccine availability right now. I actually like to just look at the FDA and the CDC ACIP [Advisory Committee on Immunization Practices] websites directly to see what the authorization says. … But those are very high effort sources, and so I recognize that a lot of people are not going to want to wade into the approval documentation.
I am very concerned about the vaccine availability for autumn. The approvals on the FDA side have come in, but they’re very limited to older adults and people with underlying health conditions. And it seems likely that ACIP is going to be similarly restrictive. For a listener or a reader who wants to get vaccinated, there will be ways. On an individual level, I think it’s possible to get coverage, but on a population health level, I’m very worried that people are not going to be able to get easy access to that protection.
On an individual level, I think it’s possible to get [vaccine] coverage, but on a population health level, I’m very worried that people are not going to be able to get easy access to that protection.
Caitlin Rivers
BL: I know one thing that has just started happening is certain states trying to make it easier. I mentioned this in my own update yesterday [on September 2], but the New Mexico public health department put out a ruling that said, “We want pharmacies in New Mexico to not restrict access to COVID vaccines.” I’m curious if you’re seeing more of that or how that kind of thing can make a difference, given how state-by-state our public health infrastructure is in the U.S.
CR: Every little bit helps. And so I’m certainly supportive of those kinds of efforts to clarify policy and open up new avenues. But I keep thinking about the experience with Paxlovid, which was supposed to be administered by pharmacists, and that people wouldn’t necessarily need a prescription. And it was a mess. There were the best of intentions in terms of making it accessible. But in practice, people had a really hard time getting it.
I see the same kinds of structural barriers here for the COVID vaccine, where maybe it’s technically possible, but in practice, there’s a lot of pharmacists out there. There’s a lot of CVSs out there. There’s a lot of quirks of the system to navigate. And if you’re just someone who wants to get vaccinated and can’t jump through a hundred hoops or argue with the pharmacist…
BL: Or get a prescription from a doctor, if that’s going to be required in some place[s]…
CR: It’s so hard. Don’t get me going. It makes me so frustrated. To make people go to the doctor … That’s so counterproductive.
BL: Same. It’s just so frustrating. Is there anything else that you would want people to know as we’re starting to head into the fall and winter, when COVID is going to keep going around, but we’re also going to get flu and all the other stuff?
CR: Yeah. I know that [SARS-CoV-2] reinfection is really important for people to avoid, for people with Long COVID, because it can really exacerbate symptoms. But I do think it’s worth paying attention to the range of seasonal respiratory viruses, because influenza and RSV also can be quite severe. I personally prefer to take a pan-pathogen look at what’s going around for safety.
I know that [SARS-CoV-2] reinfection is really important for people to avoid … But I do think it’s worth paying attention to the range of seasonal respiratory viruses, because influenza and RSV also can be quite severe.
Caitlin Rivers
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