Smallpox vaccination provides full immunity for 3 to 5 years and decreasing immunity thereafter. If a person is vaccinated again later, immunity lasts even longer. Historically, the vaccine has been effective in preventing smallpox infection in 95% of those vaccinated.
The vaccine stimulates a person's immune system to develop antibodies and cells in the blood and elsewhere that can then help the body fight off a real smallpox infection if exposure to smallpox ever occurs.
Smallpox. The eradication of smallpox through a vaccine is seen as one of the biggest achievements in public health history — but it took several centuries to get there.
The smallpox vaccine is administered in a unique manner. A drop of the vaccine virus (called vaccinia) is placed on the upper arm. The drop is then inoculated into the skin using a two-pronged, stainless steel needle.
No matter how it was administered, the smallpox vaccine left a crater-like scar in the skin because it involved delivering a live version of a related pox virus into the body. The skin around the injection site could then get damaged and scab over, leaving a scar.
On May 14, 1796, Jenner took fluid from a cowpox blister and scratched it into the skin of James Phipps, an eight-year-old boy. A single blister rose up on the spot, but James soon recovered. On July 1, Jenner inoculated the boy again, this time with smallpox matter, and no disease developed. The vaccine was a success.
Smallpox is an acute, contagious disease caused by the variola virus, a member of the genus Orthopoxvirus, in the Poxviridae family (see the image below). Virologists have speculated that it evolved from an African rodent poxvirus 10 millennia ago.
Immunity to smallpox is believed to rest on the development of neutralizing antibodies, levels of which decline five to 10 years after vaccination. This has never been satisfactorily determined, though.
The last naturally occurring case of smallpox was reported in 1977. In 1980, the World Health Organization declared that smallpox had been eradicated. Currently, there is no evidence of naturally occurring smallpox transmission anywhere in the world.
In 1972, smallpox vaccines stopped being a part of routine vaccinations in the United States. The creation of a smallpox vaccine was a major medical achievement. But the vaccine left behind a distinctive mark or scar.
A smallpox vaccine scar is a distinctive mark that smallpox vaccination leaves behind. The scar may be round or oblong, and it may appear deeper than the surrounding skin. Usually, the scar is smaller than the diameter of a pencil eraser, though it can be larger.
In addition, the vaccine was proven to prevent or substantially lessen infection when given within a few days after a person was exposed to the variola virus. Routine smallpox vaccination among the American public stopped in 1972 after the disease was eradicated in the United States.