CASTELNAU-TURSAN, France — French duck farmer Herve Dupouy has culled his flock four times since 2015 to stop the spread of bird flu but as a wave of deadly outbreaks nears his farm once again, he says it’s time to accept a solution once considered taboo: vaccination. “The goal is that our animals don’t fall ill and that they don’t spread the virus,” Dupouy said on his farm in Castelneu-Tursan in southwestern France. “Our job as farmers is not to gather dead animals.” Like Dupouy, more and more governments around the world are reconsidering their opposition to vaccines as culling...