The immunization schedule constantly changes from year to year. It is updated annually (and sometimes more frequent than that) to adapt to the introduction of new vaccines and the elimination of old ones. It is a daunting task to stay on top of all the new changes, even for medical professionals. You may find this section to be the most technical part of the book, and don't be discouraged if you do not remember everything that is covered in this section. Keep this book as a reference whenever you need a reminder for a specific vaccine or situation.