How can a person with antibodies against a virus can be infected again?

A person with antibodies against a virus can be reinfected for several reasons. First, the virus may mutate, leading to a variant that the existing antibodies do not recognize effectively. Additionally, the immune response may wane over time, reducing the level of protective antibodies. Lastly, certain viruses can evade the immune system through various mechanisms, allowing reinfection despite previous exposure.