It doesn't have to be real. People just need to think it's real.
Controlled Fear Response
The tech to freeze dry viruses, completely retaining infectivity is 50 years old.
The powdered virus can be easily smuggled anywhere and released into the air, and is reactivated by contact with mucous membranes.
They can cause strategic outbreaks anywhere and anytime to trigger panic.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC547413/