1.21 jigawatts

US Smallpox vaccinations stopped in 1972. Assuming Marty McFly didn’t get one before the age of 4, he would have been susceptible in 1955.

Smallpox could have returned in 1985 after being completely eradicated, killing thousands.

It would be even worse when it returned in 2015, again out of nowhere.

It would be traced to Marty, who would be sentenced to death for bio-terrorism. Doc Brown’s successful jailbreak would take advantage of the electric chair’s 1.21 jigawatt charge.