He thinks it has a higher risk of long term side effects. It's nearing anti-vax territory although he does admit the efficacy of vaccines and doesn't overplay the current knowledge on side effects. It's the boogeyman of possible future side effects associated with spike proteins that he's playing into. He thinks continued use of ivermectin is safer than vax plus boosters. And he thinks they're of similar efficacy so he's choosing ivermectin.