I'm Brian Lehrer. This is my daily politics podcast from WNYC Studios. It's Tuesday, May 4th.

With us now, New York Times reporter, focusing on science and global health, Apurva Mandivili, her widely read article

that was published yesterday is called Reaching Herd Immunity is unlikely in the U.S., experts now believe.

We'll also touch with her on the announcement yesterday that the Pfizer vaccine is likely to be

approved next week under the current emergency use authorization rules

that's in effect for adults for 12 to 15 year olds. So 12 to 15 year old vaccination eligibility

apparently on the near horizon. Apurva, we always appreciate when you come on with us. Welcome

back to WNYC.

Nice to be back, Brian. Remind people how you define herd immunity for the sake of this article and what real herd immunity would do, and then we'll get into the numbers and what they mean for

our risk. So what's herd immunity and what would real herd immunity accomplish?

So the term herd immunity actually just refers to the, the level of immunity in the

population to a virus or a bacterium or whatever the pathogen is. And what we are really talking

about when we say heart immunity is this number called the herd immunity threshold,

which is some percent of the herd immunity threshold, which is some

percent of the population that we have to get to where the virus starts to run out of hosts to infect.

And so its progress just becomes very slow and we see very few cases. So that's the heart

immunity threshold that we've been trying to get to. And you report that officials used to think 60 or 70 percent vaccinated or recovered from

the virus with antibodies would provide herd immunity.

Now they think 80 percent.

Why is that?

So a couple of different things happened.

One is that in December, we started to hear about this more contagious variant B117 that was circulating in the UK.

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