What Rt value indicates that an outbreak of a viral disease may end soon?

Choose one:
Rt equals zero (Rt = 0).
Rt is less than 1 (Rt < 1).
Rt is greater than 1 (Rt > 1).
Rt equals 1 (Rt = 1).

Rt is less than 1 (Rt < 1) indicates that an outbreak of a viral disease may end soon.