I think period of protection is extremely important factor when evaluating how effective a vaccine is. Or would you call any of the traditional vaccines effective if we needed to take them multiple times a year? I would not. Clearly such vaccine is not effective on scale.

If the protection only lasts for a number of weeks it is not a vaccine but a prophylaxis, comparable to e.g. Quinine (against Malaria, once upon a time). Vaccines provide protection for a longer period of time, from years (Influenza, TBE) to lifetime (Diphtheria, Whooping cough, Measles, Polio, Pox, etc.).