>> Dr. Melinda Wharton: In the United States in 2013,
it's easy not to think much
about measles because we really don't have to.
It's pretty much gone in the United States,
but that's a really remarkable story; and that's what I'm going
to tell you about for the next 15 minutes or so, how scientists
and public healthcare officials and healthcare providers
and individual families made the decisions and took the actions
that led to measles pretty much disappearing
in the United States.
Now, the first thing you need to know about measles is
that it's a pretty bad disease; and almost all the people
who get it are children.
Now, many times it's -- it's not complicated.
There's a fever, there rash, there's cough,
there's watery eyes; but the child fully recovers and --
and is not too sick; and after that is immune.
But sometimes there's implications.
Ear infections are pretty common, so is pneumonia;
and sometimes there's serious neurological problems,
and some people who get measles die.
The next thing you need to know
about measles is it is really, really contagious.
How contagious is measles?
Well, let me give you an example.
There was a measles outbreak in a children's hospital
in the late -- in the late 18 -- in the early 1890s,
and in this hospital there were 62 children who were two years
of age or older at the time the measles outbreak took place.
Five of those children had already had measles,
so they were fine.
They didn't get measles again.
They were immune.
But of the 57 other children,
55 of them got measles during that outbreak.
Only two children managed to evade infection.
There was another interesting observation
out of this outbreak.
There were also 113 children under age two in the hospital,
and 78 percent of them ended up getting measles.
But not one of the children under six months
of age got measles; and that's
because if the mother has had measles before,
antibody gets passed to the baby and the baby is protected
for those first months of life.
So that's -- that's how contagious measles is.
In a setting like this,
almost everybody who's susceptible ends
up getting infected.
Now, historically there were island populations
where measles may have not been there for -- for decades.
And when -- when the virus finally came,
there could be really devastating outbreaks
with terrible consequences.
There was an outbreak like that in Fiji in 1875;
and the estimates are that 40,000 people died,
probably more than a quarter of the population.
This photograph was recently published in the Fiji times,
and it's the site of a mass grave from that era.
Now, you know that was the 19th Century.
Medical care is better now.
Do people still die from measles?
Well, yes, they do.
There's been a measles outbreak going on in France
in recent years; and health authorities there report
that there've been more than 22,000 cases
and there've been 10 deaths reported;
for a death to case ratio about 1 in 2200.
Even with modern medical care, people with die of measles.
Of course, without it, the risk is higher.
It's also more likely to be fatal for very young children,
for malnourished children, and for people
who don't have normal immune systems.
So what happened in the United States?
Well, for a very contagious disease like measles
that basically everybody gets, on average the number of cases
of disease are going to be about the same in a year on average
as the number of people who are born.
And so not all those cases get -- get reported, get --
get diagnosed; but what we had
in the United States before the 1960s were hundreds of thousands
of cases of measles reported each year.
We also had during the 1950s, tens of thousands
of hospitalizations and hundreds of deaths.
So that's what was going on in the United States.
Look what happened in the early 1960s, disease went much,
much lower very abruptly.
And the reason that happened was we had a vaccine for --
really for the first time that we could prevent measles with;
and it was -- it was pretty widely used.
And -- and over the next couple of decades,
many states implemented school immunization requirements.
So in order to go to school, a child had to have proof
of measles immunization.
And there were parts of the country
where basically all the kids in school were vaccinated.
Is that enough to make measles to go away?
Is that enough to stop this person-to-person transmission
for a disease that's that contagious?
Well, if we think about how disease spread,
it goes from person to person to person.
Right? And on average if each case of measles results in more
than one case of measles -- if the person managed to spread it
to more than one person --
the number of cases is going to increase.
If on average each case of measles only spreads to less
than one person, the number of cases decreases;
and if that pattern can be sustained over a long period
of time, the disease will go away.
It won't -- will no longer spread in that population.
How much of the population needs to be immune
in order for this to happen?
Well, measles is very contagious;
so with that 95 percent of the population needs to be immune
in order to not have measles be able to continue to spread
on average from person to person to person.
So what happened in the United States?
Well, we had pretty good coverage among school-age
children; and certainly in some schools almost everyone
was vaccinated.
But were outbreaks of measles in the 1980's, and it turned
out that we actually did not have a large enough population
of young people to be immune from measles
to keep these outbreaks from happening.
Even in a school where everybody was vaccinated,
we could still have an outbreak of measles;
and that's because the vaccine didn't provide 100
percent protection.
Not everybody who got vaccinated was protected.
Maybe 90 percent, 92 percent; but not everybody.
And so in a high school with 1000 kids,
everybody could be vaccinated; and there still could be 50
or 80 or 90 kids who were still susceptible,
and we could still have outbreaks.
And that's what happened in the 1980's.
So in 1989, we started giving a second dose of measles vaccine,
either before school or during school, in order to get
that level of immunity higher among kids in school.
So did that make the problem go away?
Did measles go away then?
Actually, it didn't.
We had a big resurgence of measles between 1989 and 1991,
that wasn't in those school-aged kids.
It was in the kids who weren't in school yet.
We did a very good job of getting kids that first dose
of measles vaccine before they started school; but we didn't do
such a good job of getting kid vaccinated on time,
around the time of their first birthday.
And remember, as soon as maternal antibody wears off,
children are going to be susceptible
until they get vaccinated.
And if we don't get them vaccinated on time,
we could have an outbreak; and that's what happened during
that period of 1989 through 1991.
There were more than 55,000 cases; 11,000 hospitalizations;
and 123 deaths; so we had a problem.
There was a big, national effort to get children vaccinated
on time that continues to now, as well as implementing
that second dose recommendation.
And with both of those things, getting the first dose given
on time to more kids and getting the second dose recommendation
for kids in school, measles went way, way down.
And by the middle or late '90s,
there were just a couple hundred cases a year.
Had we actually managed to --
to have the level of population immunity
that meant we no longer had that person to person
to person transmission, had we been able to eliminate it?
Well, we weren't sure.
Certainly a lot of the cases we were seeing
in the United States were associated with travel.
There were travel histories.
People had traveled.
They had spread measles to other people.
So -- so that -- that was certainly a big part of it.
And we also knew that state
and local public health officials worked really hard
to identify suspected cases of measles and work them up
and see what was going on.
But were we really sure we had broken
that chain of transmission?
Well, it turns out that different measles viruses
that are in different countries are a little bit different
from each other.
They're different enough
that you can tell them apart in the laboratory.
They can -- they fall
into different genotypes is what they're called.
Now, they're all close enough to the same
that the vaccine prevents all of them;
but they can be distinguished in the laboratory
by genetic typing methods.
And what we found was that the viruses we were seeing
in the United States reflected travel and importation
of measles virus from other places.
That virus that had caused the big resurgence
in the United States during the period 1989
through 1991 was gone.
It wasn't in the U.S. anymore.
That's not what our measles cases were caused by.
They were caused by importation from other countries.
So in 2000, a group of outside experts reviewed the whole
situation and all the information we were able
to collect and concluded that we no longer had ongoing
transmission of measles in the United States.
We had managed to break that chain,
which is really pretty remarkable.
But of course, we're still at risk.
You know, the virus can come back anytime a plane lands.
It can be imported.
It's important to maintain a high level
of population immunity.
People still need to be vaccinated.
It could come back.
It's come back in some other places.
But -- but we've been able to keep the lid on it,
and that really is attribute to a lot
of people doing a lot of hard work.
So what happens when a disease disappears?
Well, one thing that happens is that doctors don't think
about it anymore; and they may miss the diagnosis.
They may not recognize it.
They may have never seen a case; so when they do see one,
they may not make the diagnosis.
It may be delayed for a long time.
They may admit the patient
to a hospital thinking it's something else;
not implement infection control precautions; have spread;
have delays; so that's one thing that happens.
Another thing that happens is for individual parents,
they may think about the risks and benefits
of vaccination differently.
Back in an era when parents remembered measles,
they might have had it themselves,
they may remember other people being really ill with it,
it was a pretty straightforward decision to make
when it was time to vaccinate your child.
But when the disease is gone, how do you think
about risks and benefits.
Now, the measles vaccine we use is combined
with the mumps and rubella vaccine.
It's MMR, and it's a very safe vaccine.
But -- but like any pharmaceutical product,
there are side effects.
There are risks associated with vaccination.
It's just that those risks are way,
way less than the risk of getting disease.
But if you don't feel like your child is at risk
of getting the disease, is that a risk you're willing to take?
And for some parents they aren't,
and some parents make a decision to not vaccinate their children.
And what that leaves is a situation
where potentially we no longer could have herd immunity
in communities.
So what's herd immunity?
The idea with herd immunity is that a disease is passed
from person to person to person to person;
and there are some people who can't be vaccinated
because they're -- they're too young
or they've got an underlying condition,
and the vaccine's contraindicated;
or they could have been vaccinated
and think they're protected but they're not because they're one
of those people that the vaccine didn't take in.
But those people can be protected if the people
around them are immune,
which keeps the virus from getting to them.
And I've got a little animation I want to show you
that makes this point really well.
So this is a population that's completely susceptible.
Think about that -- that hospital outbreak in 1892.
And so here's what happens when measles comes through.
Almost everybody gets it.
So we go on to a situation in a community
where there's a high level of immunity.
Look here.
All these people who are green, they're all protected.
And there's some susceptible people left.
But see what happens when measles comes through.
Those susceptible people are protected
because they're surrounded
by immune people and break that chain.
So
that person-to-person-to-person transmission doesn't find them.
What happens when susceptibility is higher in that community
when not -- when not so many people are protected?
What we see is that path
of person-to-person transmission finds many
of those susceptible people.
We're not able to protect the people that can't be vaccinated
if a level -- if a level of immunity in the --
in the overall community is low.
What we've seen in recent years are outbreaks of disease
that have occurred in communities
where people have made a decision not
to vaccinate their children.
There was an outbreak like this in San Diego in 2008,
where a child came back from a trip to Europe, had measles,
managed to pass measles on to other children in the household,
in school, and in a doctor's office, where a number
of infants, who actually were too young to be vaccinated,
were exposed to measles.
And people who make the decision not to vaccinate aren't,
you know -- aren't randomly spread through the population.
They tend to go to the same schools,
live in the same neighborhoods; so there is some clustering
of susceptibility that increases risk.
Probably every one of you have heard that there --
know that there are people who are concerned about the safety
of vaccines, about vaccines and autism.
Since this issue first came out more than a decade ago,
there's been a lot of really excellent science that's been
done to address it.
And those studies have been really reassuring.
But we know that some parents do still have concerns.
A recent survey -- in a recent survey parents
of young children were asked what concerns, if any,
do they have about childhood vaccines; and 15 percent
of them said that vaccines may cause autism.
Fortunately, we know that with effective communication skills,
healthcare providers can work with -- can work with parents;
and many of them will make a decision
to protect their child by vaccination.
Now, my focus has been on the U.S.
; but of course, this is a global issue.
We are part of the global community; and any traveler
who comes into this country could bring measles
from anywhere.
We're all connected together;
and as long as measles is anywhere,
the U.S. remains at risk.
Many regions of the United States have already established
measles elimination goals.
Those are the black dates on the -- on the graphic.
And if all of the regions eliminate measles,
it will be gone.
It won't be an easy thing to do, but it's not impossible.
It could be done.
It will take a very high level of population immunity;
and what that means is --
is it's going to take a lot of political will.
It's going to take effective immunization programs
that really get into every community.
And it's going to mean that parents all over the world have
to make that decision to protect their children
by vaccinating them;
but if we do that,
measles can be gone for good.