The scar association is well established. Smallpox vaccine deposited on skin was inoculated by making multiple small punctures, and the resulting local reaction (a vesicle/pustule that scabbed over during 7-21 days of healing) commonly left a small circular scar on the upper arm.

The bifurcated needle, invented by Dr. Benjamin Rubin at Wyeth Laboratories and adopted by the WHO in 1968, uses two prongs that hold a droplet of vaccine and was pressed against the skin approximately 15 times to make multiple punctures. It became the primary tool for the WHO's global eradication campaign from 1968 to 1980.

However, it was not the only method used. Peer-reviewed reviews (e.g., Baxby, Vaccine, 2002) note that earlier and concurrent techniques included the rotary lancet, jet injectors, multiple pressure with a regular needle, and the simple scratch method, which remained popular until the end of the vaccination era. Many older adults in the U.S. and Europe (vaccinated before the mid-late 1960s) received vaccine via one of these earlier techniques, all of which could produce a similar circular scar because the underlying skin reaction was the same.

Death toll: The CDC, WHO-affiliated sources, and Our World in Data cite roughly 300 million smallpox deaths in the 20th century alone, with estimates of about 500 million over the past several centuries. "Hundreds of millions" is well within the accepted range.

Eradication: On 8 May 1980, the 33rd World Health Assembly officially declared smallpox eradicated. It is the first (and to date only) human infectious disease to be eradicated.

Vaccination discontinuation: Routine childhood smallpox vaccination ended in the United States in 1972 and was similarly phased out in many other countries during the 1970s.