How did scientists bring back she Spanish Flu?

By replacing the genes for either the 1918 virus’s surface protein

Explanation:

CDC researchers and their colleagues have reconstructed the influenza virus that caused the 1918-1919 flu pandemic.

as many times as you want

supercell thunderstorms are perhaps the most violent of all thunderstorm types, and are capable of producing damaging winds, large hail, and weak-to-violent tornadoes