There is virtually no natural market for vaccines to prevent smallpox (which has been eradicated) or anthrax (which is not contagious) or Ebola (which occurs in vicious but sporadic outbreaks).

• 有些疫苗则根本没有真正的市场需求，像是天花（已经绝迹）、炭疽（不会传染），或是伊波拉出血热（相当可怕但只是偶尔爆发）。