Vaccine makers could lobby the government to make the vaccine mandatory, thereby guaranteeing a revenue stream for the vaccine to reduce the financial risk.
(1) TotallyGenuine drug company realizes that they can still get paid giving out fake shots.
(2) NotEvil drug company buys up it's smaller competitors and stops improving vaccines.
(3) KeyboardScientist makes a viral post that the government is sterilizing people of a particular ethnicity.
With a bit of googling, you can find events very close to all these three.