00:00
it's this; you may recognize this
photo, you may recognize this disease,
this is smallpox, one of the great scourges
of humankind, one of the great burdens of
human civilization and smallpox is particular,
because it is the first human disease deliberately
eradicated by human beings and we did this
in 1980 in large part due to some innovative
approaches by epidemiologist, heroes I would
argue. So as I mentioned, smallpox was defined
to be eradicated by the WHO in 1980, but attempts
to do so go back decades before then. In 1975
this individual, Rahima Banu, I think she's
from Bangladesh was the last person to contract
natural smallpox and since then we don't know
of any individual who has contracted natural
smallpox, so we're pretty confident the smallpox
has been eradicated. I'm sufficiently old
that I still have a mark on my shoulder for
my smallpox vaccine, it left a large mark.
01:03
But young people today don't have that mark,
they don't have that burden because we have
eliminated the need for that vaccine. I love
this particular quote by Thomas Jefferson
in a letter to Edward Jenner in 1806, he says,
the critical part of this letter's is the
last sentence, "Future nations will know
by history only that the loathsome smallpox
has existed." It is important because Edward
Jenner devised the first workable smallpox
vaccine in the early 1800s and Thomas Jefferson
implies in his letter that due to that vaccine,
we will no longer have the smallpox problem.
But it took another 180 years for us to truly
eradicate smallpox, so clearly the solution
for beating back this disease wasn't simply
the technology of vaccination. It was something
a little more complicated, more profound,
more interesting, and that's where the science
of epidemiology came in. It was a need to
compute the numbers of people who need to
be vaccinated to truly eradicate the disease
and this was made possible because of something
called herd immunity. Herd immunity is when
individuals in a population are immune to
a disease and thus prevent other individuals
who are not immune from getting contact with
that disease. If you think about a herd of
cattle, those at the center of the herd will
never have any contact with anyone outside
of the herd because they're protected by those
on the periphery. So as long as those on periphery
are immuned or have been vaccinated, then the
ones in the center don't need to be, in other
words, not everybody in the herd needs to
be vaccinated, just a certain proportion.
02:44
Epidemiologist stepped in and computed that
proportion that was needed to ensure that
smallpox would be eradicated.
02:53
Let's look at the timeline of smallpox in
human civilization. Going back centuries,
if not millennia, smallpox was a major scourge
of humankind. In the 18th century attempts
at finding a treatment made some great progress
with Edward Jenner creating the first relation
attempts. But back then 400,000 people would
die every year, at least, it was quite the
killer. A third of the survivors though became
blind and so they lived on with disability,
so it is not like just about the disease killing
people, it's not just about mortality. It's
also about the morbidity and it's important
that we keep in mind that when we're looking
at the impact of disease, it's not just the
deaths we care about, it's the effects on
the quality of life that matter. The people
who survive also developed immunity to smallpox,
this is an important consideration when we
talk about eradicating the disease. Once you've
got it, you're not going to get it again,
we can cross you off the list of someone who
needs to be inoculated. So Edward Jenner took
interest in cowpox which was a kind of smallpox
that cattle had and he noticed that people
who are milking cows would be exposed to cowpox
and tended to be immune to smallpox as a result,
so he got the idea that exposure to this particular
infection, cowpox, may imbue an individual
with a kind of immunity to smallpox. So in
the 1950s, the world took notice that maybe
it was time to have a more militaristic administrative
attempt to control smallpox globally. In 1967,
a decision was made by the WHO to attempt
to eradicate and remove this scourge from
the human experience altogether and as I mentioned
in 1980 this was accomplished. The WHO had
eradicated smallpox entirely, a great triumph.
04:39
So to review that timeline, in '67, we began
the eradication process and back then 15 million
people were developing smallpox every year,
but 2 million died every year and today no
one dies anymore from smallpox.