Some infections (e.g. tetanus) do not generate herd immunity even at high vaccination rates. Why?

• Atetanus vaccine produces weaker antibodies than other vaccines
• Btetanus is not contagious between people - it is caused by a soil bacterium entering wounds; herd immunity only applies to diseases that spread person-to-person
• Ctetanus evolves too rapidly for memory cells to remain effective
• Dtetanus is exclusively a childhood disease so adult vaccination cannot contribute to herd immunity

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