Most americans born before 1970 have a permanent scar on their shoulders from the smallpox vaccine. why don't younger americans have one?

I believe the answer is: Smallpox has been eradicated by a worldwide vaccination program

Vaccines develop an immunity toward the virus. In order to survive, virus need to obtain a host so they could replicate. Due to the vaccine, the viruses cannot find these hosts. Because of this, smallpox virus started to gradually decreased and eventually eradicated.

michael joseph jackson was an american singer, songwriter, and dancer. dubbed the "king of pop", he is widely regarded as one of the most significant cultural figures of the 20th century and one of the greatest entertainers of all time.

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"harry t. moore (1905-1951) – civil rights activist, leader, and the first martyr of the civil rights movement. fannie lou hamer (1917–1977) – leader in the american civil rights movement; co-founder of the national women's political caucus and freedom democratic party. james farmer (1920–1999) – congress of racial equality."