History
of Disease

Global
Eradication of Smallpox
In 1950, the Pan American Sanitary Organization, the predecessor to the Pan American
Health Organization, undertook a hemisphere-wide eradication program that by
1967 had eliminated smallpox from all countries of the Americas except Brazil.
In the years just before this eradication process began, two million people a
year were dying of smallpox. (22:V2:11)
The reasons that smallpox could be targeted for eradication when many other infectious
diseases could not include:
1. Humans are the only known reservoir for the disease, therefore, if transmission
from human to human could be stopped, the disease could be eliminated as there
is no animal reservoir that would contribute to continued circulation.
2. Practical diagnostic tools were available to assist in the diagnosis and confirmation
of smallpox cases.
3. A vaccine was available that could effectively protect individuals from disease
for several years (or longer if repeated), therefore, interrupting transmission
was possible.
Two
technical advances laid the foundation for smallpox eradication: (22:V2:13) The
development of a freeze dried vaccine which retained its potency at tropical
temperatures, allowing use of the vaccine in more areas of the world. The second
significant advance was the development of the bifurcated needle for vaccination.
The bifurcated needle had a number of advantages over previous methods of vaccine
administration:
1. The method could be easily taught to almost any individual in 5-10 minutes.
2. Vaccination using this technique resulted in nearly 100% successful vaccine
takes.
3. The dose held between the prongs was about 1/100 the vaccine that was required
by the previous methods of vaccination, therefore, more vaccine was available.
The first proposal for global eradication was made to the World Health Assembly
by the USSR in 1958. (19:12) The Russians proposed a world-wide vaccination program
to be completed in a 3 to 5 year period. Some progress was made over the next
7 years, but the program intensified during 1967 with an influx of money and
resources.
During 1967, the World Health Assembly formed the Intensified Global Eradication
Program with the intent of wiping out smallpox. (8:2) It
was headed by Donald Ainslie Henderson, a former head of disease surveillance
at the Center for Disease Control. Their efforts were funded by a special budget
of $2.4 million per year by the World Health Assembly. The campaign was based
on a twofold strategy:
1. Mass vaccination campaigns in each country (which resided in one of the four
major endemic areas), using vaccine of ensured potency and stability that would
reach at least 80% of the population and that would be assessed by independent
teams. (19:14)
2. The four major endemic areas were Africa (specifically countries south of
the Sahara), Asia (an area extending from Bangladesh through India, Nepal, Pakistan
and Afghanistan), and the Indonesian archipelago and Brazil (which comprises
half of South America). (19:12-13)
The
mass vaccination campaigns allowed health authorities to achieve “herd
immunity.” The theory behind the development of “herd immunity” is:
in diseases that can be passed from person to person, it is more difficult to
pass that disease easily when there are those who are immune to it. The more
immune individuals there are, the less likely it is that a susceptible person
will come into contact with someone who has the disease. (22:V2:16)
The development of a system to detect and contain cases and outbreaks (surveillance-and-ring-vaccination
containment method), (8:2) became the key element in the
global eradication program. William H. Foege was the doctor who pioneered ring
vaccination. He was the first to use ring vaccination on a wide scale in Nigeria
in November 1966, as an act of desperation, because he had run out of enough
vaccine to immunize everybody
in the area of a major outbreak. (15:60) It worked well
because smallpox outbreaks
were choked off by rings of immune people. (15:60)
The last case of smallpox in the United States in 1949. (19:1) The
last known naturally occurring case of smallpox was recorded in Merka, Somalia
on October 26, 1977. Two further cases occurred in 1978 as a result of a laboratory
infection
in Birmingham, England. (8:2) The World Health Organization
officially certified that smallpox had been eradicated on December 9, 1972, 2
years after the last
case in Somalia. (19:14)
Following the declared eradication of smallpox, the 1980 World Health Assembly
recommended that all countries cease vaccination and that all countries laboratories
either destroy their remaining stocks of variola virus or transfer them to one
of two WHO reference laboratories – the Institute of Viral Preparations
in Moscow, or the Centers for Disease Control and Prevention in Atlanta. (15:105)
In 1994, the committee and the World Health Assembly voted unanimously to destroy
all the stocks of smallpox, and they set a deadline of June 30th, 1995. The British
Ministry of Defense and the U.S. Department of Defense began to object to the
plan, and the deadline passed without any action being taken. (15:105) A
new deadline of June 30, 1999 was set, but opposition to the destruction persisted. (15:105) |