Which statement about neutralizing antibodies and protection is accurate?

• A. They are used to diagnose acute poliomyelitis.
• B. They reflect mucosal immunity only.
• C. They correlate with protection against paralysis; each serotype requires immunity.
• D. They have no clinical relevance.

Answer: (C)

Neutralizing antibodies to poliovirus are a key correlate of protection against paralytic poliomyelitis, and protection is serotype-specific. These antibodies block the virus from binding to its receptor and entering cells, preventing replication and the viremia that can lead to paralysis. Because there are three distinct poliovirus serotypes, immunity must exist for each one to provide complete protection; having antibodies to one serotype does not protect against the others. Measuring serum neutralizing antibody titers is thus a standard way to assess immunity after vaccination or infection, because their presence strongly correlates with protection against disease caused by the corresponding serotype. While mucosal immunity can help limit intestinal infection and transmission, the systemic neutralizing antibody response is the best-established predictor of protection against paralysis.