AILSA CHANG, HOST:
A disease that we thought was eradicated in the U.S. almost 20 years ago is now spreading rapidly. We learned this week that the measles virus is on the rise. And if the trend continues, the U.S. is on track to have the worst outbreak on record since the disease was thought to have been eliminated in the U.S. in 2000. Measles can be fatal. It can cause deafness blindness and even brain damage.
Dr. Anthony Fauci is the director of the National Institute of Allergy and Infectious Disease. He joins me now to talk about what's behind this spread. Welcome.
ANTHONY FAUCI: Good to be with you.
CHANG: So why are the numbers going up at such a startling rate right now?
FAUCI: You know, it's really the unfortunate situation of people not vaccinating their children. And the level of coverage in a given community, when it falls below a certain critical level, you get the kinds of outbreaks that we're seeing, particularly in places like New York City and the Williamsburg section of Brooklyn, where the percentage of a given community - and this is a relatively closed community, a Hasidic Jewish community in that area - that are not vaccinating their children at a rate that would provide that broad umbrella of protection that we call herd immunity. And...
CHANG: Right.
FAUCI: ...When someone enters the community, a visitor from outside - in this case it was someone who went to Israel and came back from Israel - who is infected, then you have the kinds of outbreaks that we're seeing.
CHANG: I want to make sure I understand this phrase that you just used, the phrase herd immunity. Is it basically the minimum number of people in a community that should be vaccinated in order to prevent the spread of a disease?
FAUCI: Right. A virus does not get any momentum in a community when you have a high percentage of the people who are vaccinated. With measles, that critical level of herd immunity is somewhere around 93 to 95 percent...
CHANG: Oh, so it's quite extensive.
FAUCI: ...Of the community.
CHANG: Yeah.
FAUCI: It really needs to be very high. When you drop down to the 80s or even the 70s or even lower, where it is now in that community, that's exactly the explanation of why we're seeing the outbreaks that we're seeing.
CHANG: If you could just put the most recent outbreak in context for us - I know that a lot of outbreaks have happened in smaller communities of people that have a high rate of people who are not vaccinated.
FAUCI: Right.
CHANG: Do those outbreaks threaten people who are vaccinated?
FAUCI: No. If you are vaccinated, you as an individual are going to be safe. If you are in a community in which you're not vaccinated but there's a low percentage of people who are vaccinated, you're not going to be protected, which is exactly what's going on. But if you're fully vaccinated, if you have the two components, which is usually given from 12 to 15 months of age and then a booster at 4 to 6 years, you are protected and durably protected.
CHANG: Do you feel like we are losing the battle against the spread of measles?
FAUCI: Well, if things continue the way they are now, I do think that that is an unfortunate consequence of what's going on right now - because if people continue to under-vaccinate in communities, we're going to see more outbreaks. And I think the more important point is that people sometimes incorrectly and inappropriately think that to get infected with measles is a trivial disease. It is not. It can be very dangerous because if you look at the history of measles prior to vaccinations that were available throughout the world, there were a couple of million deaths per year with measles.
In the United States, in the mid-1960s, there were about 2 to 3 million cases of measles and about 500 deaths per year. So we should not consider measles as an insignificant disease. And that's the reason why we're so frustrated when we see the outbreaks that are occurring throughout the country, particularly now - currently, the large outbreak in New York City.
CHANG: Anthony Fauci is the head of the National Institute of Allergy and Infectious Disease. Thank you very much for joining us today.
FAUCI: Good to be with you. Transcript provided by NPR, Copyright NPR.