Vaccines are certainly useful. Getting sick easily is a problem of one's own constitution, which may be that the body has poor adaptability to changes in the external environment and has nothing to do with vaccines. The function of vaccine is to improve the body's immunity to a pathogen. Each vaccine is aimed at the pathogen of one or several diseases and cannot directly improve physical fitness. Of course, the more vaccines, the better. You can choose some vaccines for childhood diseases and endemic diseases.