Herd immunity protects against diseases with person-to-person transmission. Which disease cannot be prevented by herd immunity?

Correct option is C

Tetanus is not transmitted person-to-person; it results from spores entering wounds. Thus, herd immunity cannot protect against it — only individual immunization works.
Explanation of options: (a) ✘ Measles spreads human-to-human, herd immunity is effective. (b) ✘ Polio also spreads via fecal-oral route, herd immunity helps. (c) ✔ Correct; tetanus is non-contagious, herd immunity has no role. (d) ✘ Rubella is contagious and herd immunity prevents outbreaks.