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CDC director on new isolation rules

ARI SHAPIRO, HOST:

It took less than a month for the omicron variant of the coronavirus to account for nearly 60% of the cases in the U.S. That's according to estimates by the Centers for Disease Control and Prevention. Yesterday, the CDC issued updated guidelines for people who test positive, and they include a big change - people with no symptoms can now isolate for just five days instead of 10 if they wear a mask around others for the next five days. CDC Director Rochelle Walensky is here to explain the thinking behind this new guidance. Welcome back to ALL THINGS CONSIDERED.

ROCHELLE WALENSKY: Thanks so much, Ari. Glad to be with you.

SHAPIRO: What ultimately changed your mind on cutting the isolation period in half?

WALENSKY: Well, there were actually a confluence of events, I think, and a confluence of science. First of all, we are standing on the shoulders of now two years of science and a lot of information that we've gleaned from wild-type variant, from the alpha variant, from the delta variant and now what we are learning from the omicron variant. And what we have learned during all this period of time is that early in the course of illness, in the one to two days prior to the onset of symptoms and in the two to three days after the prior onset of symptoms is really when the vast majority of transmission occurs. So in that five-day window is really where most of that transmission is happening. So really...

SHAPIRO: How new is this science? Is this a decision that could have been made some time ago?

WALENSKY: Well, you know, really, what we're trying to do here is this confluence of events. This is the science that we have seen. And of course, there is a bit of transmission that still can occur in those last five days. But what we started to see over this last several days is what's going to happen here with omicron, with a really large anticipated number of cases. And as we've seen that, we also want to make sure that we can keep the critical functions of society open and operating. We started to see challenges with that, you know, with airline flights and other areas. We started first with doing the health care workers last week to make sure that we could make - keep our hospitals functioning safely and open.

SHAPIRO: So I hear saying that while the science is a factor, the science isn't operating in a vacuum. There are economic and societal concerns beyond just health and safety. Given that people can still shed the virus after five days, why not mandate masking or even require people to test negative before they end isolation?

WALENSKY: Yeah, I really am glad you asked that question. So of course, we can't take science into a vacuum. We have to put science in the context of how it can be implemented in a functional society, so we always do that. Your question, though, is really important. And that is, you know, the vast majority of transmission happens in that first five days. And there's probably a little bit that might happen after those five days, which is why we've really put in the strong recommendation to mask those last five days. And I will reiterate that this guidance only works if people follow it and mask for those last five days. But the question of a test, I think, is a really important one.

And what we've learned from the science is that we know that a PCR test can remain positive for up to 12 weeks after your initial infection. So if we're looking for that to guide us, it won't work. The antigen test is another question that has arrived, and interestingly, we actually do not know the predictive value of the antigen test later in the course of disease with regard to transmissibility. And the fact...

SHAPIRO: Predictive value meaning whether you can infect somebody else, even if you test positive on one of those tests.

WALENSKY: Exactly. And in fact, the value of those antigen tests we've learned is when you have symptoms, first of all, when we can diagnose you and also when you use them serially, like you do in a test to stay in a school setting or in a higher education setting.

SHAPIRO: I do want to ask you about the availability of at-home rapid tests. But before we get to that, this guidance applies to asymptomatic people. And I wonder if that's a subjective standard, particularly when people are facing lost income or their bosses are pressuring them to get back to work. Are you trusting people who've tested positive to act in good faith and attest that they are asymptomatic?

WALENSKY: Well, we're trusting them to get the test to begin with. We're trusting them to stay home and to isolate for those first five days. We're trusting them to protect each other and one another and to wear a mask in those last five days. And yes, we're trusting them to also include their symptoms as part of that calculus. So yes, I think that we as a society need to trust people to do - to follow all of the components of this guidance.

SHAPIRO: Yeah. On the subject of testing, we're seeing lines around the block in some cities. The Biden administration has, of course, ordered hundreds of thousands of new tests. But how long do you think we are going to see these shortages that we've been seeing all through the holiday season?

WALENSKY: Yeah, this is an area where we are working actively. The government is doing a lot, and we clearly need to do more. We have 20,000 PCR, free PCR sites that are up and available now. And just with the testing crunch in New York City, for example, we have added at least six or seven new federal testing sites in New York. As you noted, more and more rapid tests becoming available online - the FDA is authorizing them - but now also a half a billion tests expected in January. So this confluence of travel and the surge has really led to - the omicron surge has led to a higher demand of testing, and I will add, not just even in this country, but a testing shortage really around the world.

SHAPIRO: Given the shortage in the U.S., do you think that the official number we're seeing right now of an average of 200,000 new cases a day might actually be lower than the reality?

WALENSKY: I think that we are not adequately capturing all of the positive antigen tests and not everybody who tests by antigen. So this is probably an undercount of where we are, yes.

SHAPIRO: On that topic, last week the CDC said that omicron accounted for three-quarters of cases in the U.S. in mid-December. Now your agency says it was actually around 23% of cases in mid-December. That's a pretty big difference. How accurate a picture do you have right now about what's actually going on with the omicron variant?

WALENSKY: Yeah, it's a really important question. So what we do know in our estimates from yesterday are that, you know, it varies across the country. In some regions of the country, it's at 25%. In some regions like New York, we're estimating it at around 88%. Of course, when we're using small numbers and we do these projections, we are using the best numbers that we can and projecting them to our best availability of the data at hand. And as those data improve, as we get more numbers, our estimates get more precise, and that's exactly what happened here.

SHAPIRO: I want to note, I mistakenly said the Biden administration had ordered hundreds of thousands of new tests. Of course, I meant hundreds of millions of new tests.

WALENSKY: Right, yeah.

SHAPIRO: Dr. Anthony Fauci said he thinks it's reasonable to consider a vaccine mandate for domestic flights. What do you think on that point?

WALENSKY: You know, I think any - we consider all policy, you know, potential in policy. Here's what I know. I know that the CDC strongly recommends vaccination for everyone. I know that the CDC strongly recommends boosting for everyone who is eligible. And I do know that if you are in the hospital now, you're 17 times more likely to be unvaccinated than vaccinated. If you are a fatality case right now, quite sadly, you are 20% - 20-fold less likely to be boosted compared to somebody who is boosted. So right now, what we're talking about is ways to get people vaccinated. Certainly, domestic flights has been a topic of conversation, but that is not something we're revisiting right now.

SHAPIRO: On the topic of people who are not vaccinated, when you look at areas that vaccination is lagging, from boosters and adults to unvaccinated kids to adults who refuse to get vaccinated at all, where do you think public health and medical experts should be focusing their energy to make the most difference right now?

WALENSKY: I think we need to listen. We need to talk to people and listen. We need to focus on our most frail and elderly populations, those who are who have underlying medical conditions, because those people are ones who may not yet be - who may be vaccinated and not yet boosted. And it's really critical in the context of omicron to get them boosted. And then I think we need to spend some time talking to parents and to listen. You know, not every parent wants to have all the data at them. They want to sort of give you their concerns and then have you speak to their concerns, and that's the hard work we're doing every single day.

SHAPIRO: If I could end by just asking you to look ahead, even as case numbers skyrocket and hospitalizations go up, many people are looking at South Africa's experience with omicron, and they express hope that this spike may be over soon and may not lead to a proportionate increase in deaths. Does the evidence you're seeing support that forecast?

WALENSKY: Certainly, that would be great news. I think we have to be cautious as we extrapolate what is happening in South Africa with what is happening here because they have so much underlying immunity in South Africa. That said, much of what we're hearing about are mild cases, and that's heartening. But what I would also say is that if people are not vaccinated and boosted, you know, we really can't predict how this is going to go, and the hospitalizations are really focused on, you know, people who haven't been vaccinated yet. So that's really our bottom-line message.

SHAPIRO: CDC Director Rochelle Walensky, thanks so much for your time today.

WALENSKY: Thank you. Transcript provided by NPR, Copyright NPR.