Rabies does not show signs of infection in humans for about 45 days, and I assume that is where you are confused. Typically, an individual has around 10 days following exposure to be vaccinated for rabies. The single dose vaccine is effective for between 3 and 10 years depending on the strain. For animals such as cats and dogs, most vaccines are good for 3 years, although many local laws require yearly shots despite manufacturers claiming this to be unnecessary.