Tin foil hat on:

O- is a universal donor. They need those folks alive to harvest more blood in the future. AB+ people are universal recipients which means their blood is useless for everyone else that's not AB+. If you're gonna design a bio-weapon, you wanna avoid killing off O- types because you still need to harvest blood from them in the future.

AB+ types though? They can live off of any blood type donations so they're not reliant on supplies plus their blood is useless for harvesting. If there is a Cartel for blood like Big Dairy, AB+ people are the least dependent on the supplies which makes them the most difficult to control.

Tin foil hat on:

O- is a universal donor. They need those folks alive to harvest more blood in the future. AB+ people are universal recipients which means their blood is useless for everyone else that's not AB+. If you're gonna design a bio-weapon, you wanna avoid killing off O- types because you still need to harvest blood from them in the future.

AB+ types though? They can live off of any blood type donations so they're not reliant on supplies plus their blood is useless for harvesting. If there is a big cartel for blood like big Dairy, AB+ people are the least dependent on the supplies which makes them the most difficult to control.

Tin foil hat on:

O- is a universal donor. They need those folks alive to harvest more blood in the future. AB+ people are universal recipients which makes their blood is useless for everyone else that's not AB+. If you're gonna design a bio-weapon, you wanna avoid killing off O- types because you still need to harvest blood from them in the future.

AB+ types though? They can live off of any blood type donations so they're not reliant on supplies plus their blood is useless for harvesting. If there is a big cartel for blood like big Dairy, AB+ people are the least dependent on the supplies which makes them the most difficult to control.