If the rabies vaccine is given by the four-dose method after exposure, only four doses are given for the entire course and can be effective. However, if the rabies vaccine is given by the five-dose method, only the first four doses may produce rabies neutralizing antibodies, and the amount of rabies neutralizing antibodies may reach a relatively high value. However, without a fifth dose of rabies vaccine, it is likely that the neutralizing antibodies will not be maintained for very long. With five complete doses of rabies vaccine, the corresponding neutralizing antibodies are maintained for a relatively long period of time, usually about three years, and at least more than one year. If four doses of rabies vaccine are given, there may be a subset of people for whom the neutralizing antibodies last for a shorter period of time. The rabies incubation period is less than one year. If the rabies vaccine allows the body to produce antibodies down to negative, but the rabies incubation period is particularly long, it is possible that rabies will not be prevented at this point, so it is recommended that the last shot be given.