Lizzie O'Leary: It's The Takeaway. I'm Lizzie O'Leary, host of the podcast What Next: TBD from Slate, in for Tanzina Vega this week. In the earlier days of social distancing, we heard about herd immunity as a means to ending the pandemic, that reaching a certain threshold of the population, gaining immunity through vaccinations or natural infections that the coronavirus runs out to people to spread to and things can go back to the way they were.

Recent reporting from The New York Times found that experts think herd immunity in the US is unlikely. Slipping vaccination rates combined with new variants and vaccine hesitancy makes it less likely we'll reach herd immunity anytime soon. Joining me now to discuss her reporting on the subject is Apoorva Mandavilli, a science reporter at The New York Times. Hi Apoorva.

Apoorva Mandavilli: Hi.

Lizzie: Apoorva, in the early moments and months of the pandemic, we talked about herd immunity as this concept is like the best way to beat the pandemic. How has that changed?

Apoorva Mandavilli: You're right, Lizzie, we did all talk about herd immunity as the goal, and that's because that's how it's worked for a lot of other infectious diseases. For example, for measles, you vaccinate enough people, you get to a point where enough people are protected from the virus that the virus no longer gets around as easily. What's changed now is that the two big things have happened. One is that around December new variants started to come up of the virus that are more contagious and herd immunity is based on a measure of contagiousness. With more contagious virus, the percent of the population that needs to be protected goes up. It was estimated to be 60% or 70% last year, now the number is 80 or more.

Second thing that happened is that as you know, there is a substantial proportion of the population in the United States that is really hesitant, does not want to get the vaccine, may not get the vaccine. Those two things have led scientists to conclude that herd immunity is extremely unlikely.

Lizzie: Yes. You reported that in The New York Times and it was a story that landed with a splash. Should we interpret that as a sort of disappointing sign or is it just that we should have a different goal?

Apoorva Mandavilli: Yes, I wouldn't interpret this as disappointing, I think it's just a different way of looking at it and really what we need to do has not changed at all. What we still need to do is vaccinate as many people as possible so that we really bring down the number of hospitalizations and deaths, and that has not changed. What has changed is that we probably will not be completely rid of this virus when we get to this herd immunity threshold, which is what we had been hoping for. We will probably see outbreaks of the virus for many years to come. How big those outbreaks are will really depend on how close we get to herd immunity, what percent of the population we can vaccinate.

Lizzie: Yes, I guess I think about this in two ways, the public health messaging part of it, and then how we as a society deal with whatever happens next. I wonder if people are going to receive this message and think, wait a minute, they're moving the goalposts on me again.

Apoorva Mandavilli: There is a real danger of that. When I spoke to Dr. Fauci, he was worried about that as well, because that happened to him a few times now that people accused him of moving the goalposts, but I don't think that's what's happening here. I think the goalposts have moved themselves because of the biological behavior of the virus and because of the behavior of the human beings in this country. It's not the experts, it's this is just what has happened because of those two big factors.

Lizzie: What do you think that means we're left with in terms of managing the virus over the next months or years?

Apoorva Mandavilli: We have to keep our eye on the prize. The prize is bringing the numbers of hospitalizations and deaths down, easing the pressure on the healthcare system, and getting to a point where the majority of people who are getting infected are young and healthy so that they're not having severe infections. We want to protect as many of the high-risk people, the elderly, and the people with other conditions that put them at risk as we can so that really the infections that we do see are as mild as they could be.

Lizzie: Just over 30% of the US population has been fully vaccinated. It's a larger number for having had one shot. Talk to me about how quickly vaccine penetration and distribution means for the ability to achieve something resembling herd immunity, or I don't know, what kind of a vaccine percentage you'd like to see.

Apoorva Mandavilli: I think we would need to see 70% to 80% to really start to see herd immunity, but we could probably see effects closer to just 50%. That's sort of what's been happening in Israel. We also reported yesterday, my colleagues and I, that the FDA is expected to authorize the vaccine for adolescents 12 to 15-year-olds. Yes. Then the vaccines for younger kids than that is not going to be that far behind. Even if there are a bunch of adults who are unwilling to get the vaccine, if we can vaccinate as many of those kids as we can, we might still get pretty close to herd immunity, 60% let's say without actually having to crack every single adult into getting the vaccine.

Lizzie: I think one thing that people are trying to understand now is how the US fits into this broader picture. Should we still be aggressively pursuing these vaccination and immunity goals in the US if the virus is still spreading so quickly in other places and how do those things fit together?

Apoorva Mandavilli: There are a couple of different complicated issues there. One is, we do want to be vaccinated as a country. We do want to protect as many of our citizens as possible, but at the same time, I'm originally from India, and Brazil and India are having these enormous, enormous epidemics with just so many infections. There's an ethical issue there as well of do we want to be vaccinating our kids who are not really at high risk when there are high-risk adults dying by the thousands in other countries.

That's a very difficult question to answer for a lot of people because I can see just from responses to social media when this has come up, that people are very divided. There's one side that adamantly believes that this is unethical, but we really should be giving away these doses to the countries who really need them. Then the other side says, let's take care of ourselves first before we start to take care of others.

There is an argument to be made for that as well because as the infections keep raging on in other parts of the world, we might see more variants and some of those variants are going to be more contagious. Some of them are going to evade the immune system. We do want to protect our citizens from those threats as well. It's not really an easy or simple answer.

Lizzie: Apoorva Mandavilli, is a science reporter at the New York Times. Thank you so much for this.

Apoorva Mandavilli: Thank you.

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