  Vaccination is an important measure available for preventing or reducing the
spread of infectious diseases. In this paper, an epidemic model including
susceptible, infected, and imperfectly vaccinated compartments is studied on
Watts-Strogatz small-world, Barab\'asi-Albert scale-free, and random scale-free
networks. The epidemic threshold and prevalence are analyzed. For small-world
networks, the effective vaccination intervention is suggested and its influence
on the threshold and prevalence is analyzed. For scale-free networks, the
threshold is found to be strongly dependent both on the effective vaccination
rate and on the connectivity distribution. Moreover, so long as vaccination is
effective, it can linearly decrease the epidemic prevalence in small-world
networks, whereas for scale-free networks it acts exponentially. These results
can help in adopting pragmatic treatment upon diseases in structured
populations.
