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In the past week, you may have heard about Olympic athletes who are fully vaccinated getting positive Covid tests or people in Provincetown, Mass., or Texas Democrats or the New York Yankees. These are called breakthrough infections, and they’re causing a lot of anxiety about whether the vaccines hold up against the hyper-transmissible Delta variant.

But how concerning are they? And as cases are surging across the country, how much do they matter as a metric of the pandemic when we have a vaccine to protect against severe disease?

STAT spoke with Céline Gounder, a clinical assistant professor of medicine and infectious disease at NYU’s Grossman School of Medicine, host of the “EPIDEMIC” podcast, member of the Biden-Harris Transition Covid-19 Advisory Board, and a member of the class of people we are calling pandemic celebrities.

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This interview has been condensed and edited for clarity.

Dr. Gounder, how concerned are you about these instances of breakthrough infections in people who are fully vaccinated?

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I think we really need to better define what we mean by breakthrough infections. That’s really a catch-all for people who might have an infection with no, or very mild, symptoms, all the way to somebody who might end up in the ICU, or even dead. What concerns me is breakthrough disease — people who have significant symptoms, who are struggling to breathe, who are ending up in the hospital, and we really haven’t seen breakthrough disease with the vaccines.

We’ve seen a lot of criticism in recent weeks about the way the CDC is handling the release of data and tracking of these breakthrough infections. Do you think their actions have been sufficient or is there more information that you think we need to have from from federal regulators?

I really think we should be tracking breakthrough infections. And here’s why. Those people who are still getting infected despite being vaccinated, they may not get sick, but it is possible that they could transmit the infection on to others. And so that’s something we still don’t really have a handle on. There is some evidence from the sports leagues, where they do a lot of testing, that some of these people may, in fact, be contagious. And so that is concerning.

The second reason that we really want to be tracking breakthrough infections is for what we call genomic surveillance, which is where we look at new variants that are starting to emerge and what do those look like? You’re more likely to find new emerging variants among people who have breakthrough infections. We’re sort of flying blind with respect to that, because we’re not assessing those breakthrough infections.

All this talk about breakthrough infections or breakthrough disease has also raised the issue of boosters, whether Americans will be required to go back and get reinjected with Covid vaccine. What are your thoughts on that?

First of all, booster is really not the right terminology here. I think the problem with boosters is when people hear that word, they’re like, oh, well, it’s going to be like a flu shot. I’m going to need to get a shot every year. The way I would frame this is much more like, say, a blood pressure medicine that your doctor prescribes you — where you start at one dose and they might adjust the dose over time. Just because we are still figuring out the best dosage regimen for the Covid vaccine does not mean that the vaccines don’t work, and does not mean you’re going to need a yearly Covid shot.

That’s really interesting. Where do you fall on the J&J vaccine and the current information we have about it? There’s so much anxiety because it’s just one dose. There are people who got J&J who are feeling not fully vaccinated with one shot. What do you think?

So first of all, the CDC is looking at this. In fact, the CDC’s ACIP, which is a group of people who advise the CDC on their vaccination guidelines, is meeting today as we speak to evaluate whether additional doses of vaccine should be given, specifically in this case for people who have immunosuppression. But I anticipate they will be looking at other categories of patients as well.

With respect to the J&J vaccine, I think it’s really important for people to understand that this is a very good vaccine. This is why we thought that one dose would be sufficient. Now, what we’re learning is that, particularly against some of these new variants, that one dose of J&J may not be enough. And I think what you will see over the next month or two are recommendations, at least for some subsets of people who got J&J, that they do get an additional dose of vaccine. The other thing that we’re seeing is when you mix and match different types of vaccine, so say J&J, which is very similar to the AstraZeneca vaccine. If you mix and match that with one of the many vaccines like Pfizer or Moderna, you actually get an even better immune response. So I do think you’re going to see more mixing and matching in the future as well.

So sort of a separate matter: We’ve seen cases on the rise across the United States. And as you mentioned, there’s this important differentiation between what might be a positive test versus what might be symptomatic disease or something more serious. And we know that vaccines are effective at limiting severe disease. But at the same time, cases are going up. How should we look at this when we have a relatively high vaccination rate and a lot of available vaccine for anyone who might want it? How should we perceive these rising case counts? How worried should we be, you know, vis-a-vis last year when there were no vaccines?

We are seeing this decoupling between cases and hospitalizations and deaths. So what we mean by decoupling is we’re seeing the cases shoot up more steeply than we are seeing hospitalizations and deaths shoot up. That said, it remains to be seen whether that decoupling holds because we’re still early in our own surge with Delta. And unfortunately, there are parts of the country that really have very low vaccination rates. And we don’t know how much some of these breakthrough infections among vaccinated people might then be contributing to onward transmission and circulation of the virus among unvaccinated people. So that’s really a black box at this time.

It seems like the rise in case counts has also resurrected the whole mask debate and whether we need to be wearing masks. Do we need to think about going back to wearing them?

So this is a really good question. Many local municipalities are looking at this question right now. I was on a call with several New York City public officials yesterday where they were asking for my advice on this question. I think, unfortunately, with the rise of Delta, which is about a thousand times more infectious than the original strains of the virus, we really do need to think about layering protections. And so what are those layers? Vaccination. But some of the other layers that we should consider would be masking indoors when you’re outside of your household bubble, optimizing ventilation in the home — just opening your window works really well. It works even better than many of those units that you can buy to filter the air. I think people really underestimate the power of opening windows. And finally, socializing outdoors as much as possible to minimize your risk. Those would be the things that I think we do need to be thinking about. At the beginning of the pandemic, the CDC said that a close contact was somebody that you’re indoors with unmasked for 15 minutes or more. The equivalent of that with the Delta variant is not 15 minutes, it’s one second.

Does the indoor/outdoor difference in protection still hold? Let’s say, somebody is worried about their unvaccinated child playing in the playground. Is it OK if they’re not wearing a mask?

The way to think about your exposure is dose times time. So your dose is a reflection of how much virus the person is carrying, but it’s also diluted in the air around them. So if you’re indoors, there’s not a lot of air dilution unless you’re opening up windows and doing that sort of thing. When you’re outdoors, it’s almost infinitely diluted. And so outdoors, your risk is really low. I think the only places that would concern me outdoors is if you’re packed in together with people, say, at an outdoor concert or in an outdoor sports sporting event. But in general, outdoors is really pretty safe.

That is reassuring. How are you looking at where the pandemic goes from here? There were a lot of stories a couple of months ago thinking about how does this pandemic end. But we’re in a fourth surge now. And of course, many countries don’t have access to the vaccine yet. How much longer is this going to go on?

Well, remember, pandemic means around the world, so across multiple continents. So if you’re asking, you know, when is the pandemic going to be over? It’s going to be years before this is over. I think what really worries me as somebody who, for the better part of my career, worked in HIV and tuberculosis, those are pandemics. You’re looking at about 3 million or so people dying from TB a year. A similar number of people dying from HIV per year. And that’s something that’s been going on for decades. And so I think this is going to become another disease of the poor and marginalized as the pandemic continues to evolve.

To listen to the full interview, check out the latest episode of “The Readout LOUD” podcast.

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