Podcast: Can You Get Reinfected?

The Brazil variant raises a scary question—and reminds us that herd immunity matters across borders.

An unexpected second wave of the virus has hit Manaus, Brazil—and brings with it new worries about reinfection. Staff writer James Hamblin explains to producer Katherine Wells what’s going on there and what it could mean for the rest of the world.

Listen to their conversation on the podcast Social Distance, along with a special airing of the first episode of The Experiment, a new show from The Atlantic and WNYC Studios:

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What follows is a transcript of the episode, edited and condensed for clarity:

Katherine Wells: The last time we spoke, we talked about the variants. And we didn’t know much, but it seemed like it was possibly going to be fine. But now I read what you wrote recently about the variants, and it seems like it’s not fine.

James Hamblin: Well, it’s complicated. Right now, the variants mainly pose a threat to unvaccinated populations. And the vast majority of the world is not vaccinated and will not be for maybe a year.

The city of Manaus in the rainforests in Brazil was one of the hardest-hit cities early on. They had those scenes where the hospitals were overwhelmed and there were mass graves. There were catastrophic losses—and, by estimates of scientists in Brazil, about 75 percent of the people there were infected by the virus.

Wells: So that’s herd immunity, right?

Hamblin: Well, you would think that. And after they had this very bad surge in April and May of last year, and it became their winter. And [then] they were able to open up without it getting worse. They had some restrictions in place, but they were through the worst of it.

Wells: And so, because they went through a winter without being locked down and didn’t have a huge outbreak, that suggests that there’s a high level of immunity in the population there?

Hamblin: Yeah, with 75 percent of the population infected at one point and not seeing a big outbreak in their winter, the assumption was those things taken together meant that they were through the worst of it. [But] then, in the last month, they have been overwhelmed once again, and even worse than before. The public-health officials there say it came on even faster than before—and again, in the very same city.

Wells: So the population that went through this horrific thing nine months ago is going through it again, even though most people got the virus the first time?

Hamblin: Yes. So, how is that happening? And I think there are three things to consider. One is the data might have been in error, and they didn’t have quite 75 percent of people being infected. But it wouldn’t be too far off, and even if it were pretty far off, it still shouldn’t have led to what we’re seeing.

The second is waning immunity. It’s been nine months since that first surge. How many of these people—especially if they had a mild or asymptomatic case—how many were just less immune now? Immunity seems pretty durable, and more severe illness seems correlated with a longer-lasting immune response. We haven’t seen waves of reinfection, and that is what appears to be happening here.

But then there’s this third variable which complicates that—which is this variant in Brazil. We know that variant has mutations that can help it evade the immune system. So it seems to likely be a combination of people’s immunity waning and this different strain being somewhat effective at evading existing immune mechanisms. Now, that doesn’t mean this strain would affect every population the same way. It could have been a sort of perfect storm of circumstances here. But that’s what we really need to understand.

Wells: That seems really troubling. Do we know anything about whether this Brazil variant can infect people who’ve had a vaccine?

Hamblin: There’s no evidence of that. And none of these vaccines are perfect. But when you get a whole population that’s vaccinated, they should be effectively perfect. And they are perfect at preventing severe disease so far. So it shouldn’t be scary to people who’ve been or are planning to get vaccinated. I don’t think that changes the game—but it does remind us that we have so far to go in the world. There are places in the world that we were assuming were going to be pretty safe because they’d been through the worst of it. But this raises questions about whether they’re going to go through another nightmare scenario. I don’t think it’s likely in the U.S. and other wealthy countries. But there is a lot of the world that won’t have access to the vaccine until 2022, possibly even 2023.

We focus on the U.S. a lot. And these variants sort of remind us that getting people around the world vaccinated is not just about moral obligation or empathy. The nationalist approach to vaccination is not in anyone’s national interest. Because if the U.S. got to 100 percent vaccination and there were 30 countries that were at 10 percent vaccination—because every time the virus is transmitted, it mutates—you’d still have this capacity for new strains to develop. If you just let it run wild over a lot of the world, it very well has the capacity to someday come back in a form that can work around our vaccines.