The frequency and need for vaccinations will vary. For example, strains of the flu are different every year, so annual vaccination is important. For COVID-19, the need keeps changing. Boosters have been helpful, but new strains keep developing and vaccinations against those can be important. For diphtheria and tetanus, boosters are required every ten years. There are many vaccines that will require only one shot. For these, the immunity they create remains, and boosters are not required. There are other vaccines that become more important as people get older. Vaccines for shingles and pneumococcal virus are essential as people age. These may require one or two shots.