Flu Shot Frequency. The flu shot takes up to two weeks to take effect and leave you completely immune, so getting it earlier in the season is beneficial. Even though both vaccines can be given at the same visit, people should follow the recommended schedule for either vaccine:
2 (given 4 weeks apart) 1. Is the flu vaccine safe? People of any age who have recently had a haematopoietic stem cell transplant or solid organ transplant.