Are we in a "tripledemic"?
Excerpts from my conversation on the In the Bubble podcast
I recently joined Dr. Bob Wachter on In the Bubble with Andy Slavitt, a podcast that started as a pandemic-focused show that has since evolved to cover news and current events. The show hasn’t forgotten it’s roots though—Bob and I discussed the “tripledemic” of COVID-19, RSV and influenza, and what it all means for you and your family. Excerpts of the first half of our conversation are included below, but I encourage you to listen to the whole podcast.
(Update: just to clarify, Dr. Wachter interviewed me. He is in bold, I am in regular text below.)
Bob: Let’s start with this scary word: tripledemic. Walk us through what this means and what the three viruses are.
Caitlin: “Tripledemic” describes a scenario we may be heading into this winter where we are facing not just COVID-19, but also a resurgence of influenza and RSV or respiratory syncytial virus. And the idea is that these three viruses may give us a bit of a walloping this winter. And so I’m watching the science closely to see how this season gets started.
Does a Covid infection protect you against flu or RSV and also does vaccination for one protect you against the others?
Covid infection does not protect you from flu and it does not protect you from RSV. Many people think of RSV as a virus that mostly affects children. And that is true, but you also get reinfected with RSV across your life. So it's would not be out of the question to get all three in a single season. And similarly, vaccination for one does not protect against either of the other two.
We’ve been told for the last few years that the immune system is incredibly smart and clever and adaptive. Why isn’t it smart enough that if you have immunity against one thing, you have immunity against another?
Viruses are smart too. And they have all sorts of ways of getting into your body and making you sick. And they also change very quickly. That’s why we have to get re-vaccinated for influenza every year, because the virus changes in such a way that your body doesn't necessarily recognize it from year to year.
So of the three viruses, which one is the one that concerns you the most right now?
Hmm, it depends on who you are. For children and older adults, RSV is really concerning to me right now. We're in the largest RSV wave that we've seen in at least four years, maybe longer. It's a virus that is very hard on small children and for people who are older. And so that right now is the biggest threat. But looking ahead a couple of weeks to months, it looks like this will be the year that influenza will make a big comeback.
Starting with the flu, what are you seeing as you look at the current data about the flu? Is this a particularly terrible year or is it a normal-bad flu year?
That's right, we have had a two or three year vacation from influenza, and that has set us up to have a big wave. Normally, a sizable fraction of the population gets infected with influenza every year, and the people who get infected may retain some immunity going into the next season. And that means that during a normal season, there aren't as many people who are “available”, if you will, to get infected.
But because we've skipped the last few flu seasons, there's been a buildup of the susceptible population. And that puts us in a bad spot for flu to really sweep through this year. And indeed, that is what we are seeing. We're about a month or two ahead of our normal flu season and we're already ranking to be one of the worst flu seasons of the last few years.
I will say we don't yet know about the severity of influenza this year. Certain flu seasons cause more severe illnesses than others and the data are not in yet to determine where we are in that scale.
Is that because of variants, that each year the variants we are confronted with are different than the year before?
The strain selection that goes into our seasonal that flu vaccine is done months in advance. The process usually happens spring [ahead of our flu season]. And that makes it a bit of a guessing game. Experts convene to determine what strains they think should go into the seasonal flu based on what has happened in the southern hemisphere and based on what they're seeing in early surveillance data. And that process, because it needs to be done so far in advance in order to have time to manufacture and distribute the vaccines, sometimes does not get it 100% right.
But I will say the two strains that we're seeing in the US right now are H3N2 and H1N1 and both of those are in the seasonal flu vaccine this year. So we can't say for sure that it's a good matchup, but based on what I'm seeing right now, I feel pretty good about it.
What do we know about flu vaccine uptake in a usual year?
Flu vaccine, flu vaccine in a normal year, the uptake is not great. It's around 40% of adults and in children it’s a bit higher [at 50-60%]. That leaves a lot of room for improvement. I think people are not always excited to get it because they hear that it may not work, and you have to get it every year. Why bother? I'll tell you I've got my flu vaccine and I make sure my family does too because it really can save you from a week or two of feeling very crappy.
Is the flu vaccine indicated for everybody?
It's indicated for everyone [over the age of 6 months], yes.
You frame it that the reason it might be worse now is that we all had a few flu-free years and our immune systems got a little sloppy when it comes to flu. What do you think the relative absence of masking is doing to flu?
I think masking is effective at preventing respiratory viruses from circulating and what helped for COVID, hat was implemented for COVID, also helped for flu.
But just to return briefly to one point, it's not our individual immune systems that got sloppy, it's that so many people were spared infection that there is now a lot of population level susceptibility. There's some misinterpretation that I see online [that supposes that the large waves of flu are RSV are because] our individual immune systems may not have gotten the workout that they needed to stay healthy. That's not the case. It's really a population level effect that has put us in a position to face a fairly big year.
What do you think of the plan to give once annual COVID-19 boosters?
Think it makes sense from a public communication standpoint, it has been hard for people to keep up with the changing recommendations around vaccines. [Questions like] “which dose are we on? Am I eligible?” And so I think for the purposes of clarity, it makes sense. But I do worry about people who are medically vulnerable and at risk for severe illness, because based on what we've seen so far, a single shot is not likely to protect against severe illness for an entire year. And so I hope that there is some flexibility for people who may need that mid-year booster.
Let’s switch gears to RSV. Tell us a little about what RSV is and what it does.
RSV is a viral infection that spreads very easily through droplets through aerosols and through contaminated surfaces. It can last a long time on surfaces: door handles, metro rails, toys, and that kind of thing. And almost all children are infected by RSV by the age of two. So it's a very common illness. But in those young kids, it can cause breathing difficulties that can be quite severe. And we see similar effects with older adults where it can really impact their breathing.
There is no vaccine against RSV, there is a monoclonal prophylaxis, which is a treatment that prevents severe RSV for the youngest children at highest risk, but it's a therapeutic that's used sparingly and so the punchline is we don't have a lot of pharmaceutical protections against RSV.
So when you say sparingly, I assume these are kids who immunosuppressed or have illnesses that make them vulnerable?
The indications are things like substantial prematurity, underlying lung or heart disease, these are children that are medically vulnerable because of some underlying condition.
You mentioned that a dominant mode of transmission is by touching surfaces. We all remember the early days of COVID disinfecting everything, and over time we were told that was pandemic theatre. Is that a fundamental difference in the way the two viruses are transmitted?
It's really all of the above. And I think this is true for COVID too, it's very difficult to tease out what fraction of transmission comes from these different modes. If you are in close enough contact with someone that droplet transmission becomes possible, while you're also in close enough contact that it could be aerosol and probably you're touching the same surfaces. So it's difficult to say that you're more likely to get RSV from a surface than for COVID-19. But what we can say is that the RSV virus persists on surfaces, it can live on surfaces for hours. And so that does point to sanitation and disinfection as an important risk reduction strategy along with hand washing.
You mentioned a version of the hygiene hypothesis that maybe has a different flavor in kids. The idea that the kids need exposure to viruses to develop a healthy immune system Is that part of the worry, that they haven’t had that opportunity?
No, it really is the buildup of the susceptible population, which is the epidemiological way of saying that because so many people were spared these viral infections over the last few years. there is a lot of opportunity for the virus to circulate there. There is a lot of people who can reach who may otherwise have some degree of protection. And all of that is coming all at once. So in spread instead of being spread out over three years, it's hitting now. And that's why we're seeing so many people getting sick and and children's hospitals being overrun because we're having three years of RSV season smushed into this season.
The at risk groups, you mentioned the young and old. Is it mostly babies who are at high risk?
The highest hospitalization rate is in children under the age of six months, and children under the age of one are also at risk.
Now, this is an important point. In older children and adults, RSV is no big deal often. (Of course, that's not true if you have an underlying health condition.) But, if you're a healthy, working age person, RSV presents like a cold. And it might not make you sick enough to feel like you should stay home or wear a mask, you just have the sniffles. But if that virus makes it into someone who is young, then it can be very severe. And I think that is a good reminder for us all that even if you just have a little bit of a stuffy nose, stay home when you can and wear a mask when you go out, because you may be really protecting the people who are more vulnerable.
To hear the rest of our conversation, including more on RSV and COVID-19, check out the full podcast episode. I’ll be back in your inbox soon with an update on what’s circulating.
Force of Infection is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.