with a surge of those infected.

- Measles is back in the US.

- The threat's so severe,

some hospitals arming each entrance with security guards

to screen visitors for symptoms of the virus.

- In the first few months of 2019,

US doctors reported 314 cases of measles

to the Centers for Disease Control.

Now compare that to the number of reported cases

in the year 2000.

Less than 100.

What happened?

Scientists put much of the blame

on the anti-vaccine movement,

which is thriving in some parts of the country.

- Washington state has been called a hotspot

because of its anti-vaccine movement.

- Washington state, where more than 70 cases were reported,

is one of 17 states that allows parents

to object to vaccinating their children

on the basis of personal or moral beliefs.

And with fewer kids vaccinated,

measles is far more likely to spread.

In fact, the disease is so contagious

that 93 to 95% of a population

must be vaccinated to prevent transmission.

Yet, in a number of states,

more parents are seeking nonmedical exemptions

from routine immunizations.

But here's the thing.

Overall, the US is doing pretty well

when it comes to immunizations.

If there is a big vaccine problem,

it's not here in the US, but abroad

in Africa, in parts of Asia,

and in the Middle East.

There were about 20 million infants in 2017

that didn't receive routine immunizations,

such as for diphtheria, tetanus, and pertussis,

or DTP.

And about 60% of them live in 10 countries.

In Nigeria, for example,

only a third of the population

received the third dose of DTP in 2017,

while that rate is closer to 85%

for the rest of the world.

You see, immunization rates are tied not just to beliefs

but to economics.

Poor countries often lack infrastructure like electricity,

which is needed to keep vaccines refrigerated.

Consider South Sudan.

Less than 10% of the population

had access to electricity in 2016,

which might help explain why the country

has one of the lowest immunization rates in the world.

But there are also other factors at play.

Like conflict.

Following the civil war in Syria, for example,

immunization rates for some diseases

fell by nearly 40%,

and that trend is mirrored by other countries

that are also marred with political strife.

Yes, these numbers look bleak,

but they are improving

thanks to an increase in awareness

and funding for immunization efforts,

especially in countries like Afghanistan,

Bangladesh, and Sudan.

And in 2017,

a record 123 million children were immunized

with at least one dose of DTP.

So even as this anti-vaxxer movement

grips parts of the US,

as a global species,

humans are actually closer than ever

to ridding the world of vaccine-preventable deaths.