Whoever owns, keeps or harbors a dog or cat within the boundaries of the corporate limits of the City, shall by July 1, 2017, have such dog or cat properly vaccinated or immunized against rabies with a vaccine capable of producing immunity for two years and shall every second year thereafter have such dog or cat revaccinated with a vaccine capable of producing immunity for two years. After July 1, 2017, whoever obtains an unvaccinated dog or cat shall at once have such dog or cat properly vaccinated against rabies with a vaccine capable of producing immunity for two years and shall have such vaccination repeated every second year with a vaccine capable of producing immunity for two years; provided, however, that dogs and cats need not be vaccinated before the age of three months, but must be vaccinated by the age of six months. No license shall be issued for any dog, unless the applicant exhibits a certificate by a veterinarian showing compliance with the provisions of this section.