It was the small pox vaccine.  It was "dotted" or injected under the skin to cause a reaction which often became a scab. Fortunately because of worldwide vaccination, this disease no longer exists except in a safe in Moscow and at the CDC in Georgia, USA.
 
Another similar one was the BCG for tuberculosis given in many countries but not here. It left a depressed skin mark but not a scab.
 
Wayne Yankus, MD, FAAP
expert panelist: pediatrics