There are a lot of serious diseases that can be prevented with shots, indeed a very very very (I don't know how I can stress this enough) small percentage of people get some bad reactions to the shots, but shots are extremely helpful in preventing you from getting many of the diseases that plagued the pre-modern world. I know that a lot of people in this forum have a hatred for doctors and main stream medicine, and yes doctors sometimes are wrong, and there are many things that conventional wisdom is wrong about as well, but you have to take it as a grain of salt. Main stream medicine is wrong about a great deal of thing, but they are also right about many other, and vaccination is one of them. People here like fasting who like fasting should probably appreciate the workings of a vaccine since the vaccine is nothing, but a modified or weaker version of a disease carrier. What makes the vaccine effective is the ability of your body to produce antibodies to fight off that disease. One part of fighting a disease is creating antibodies so if your body already posses the knowledge of how to produce antibodies your body will be able to fight the disease as soon as it enters your body, therefore the disease will not be able to compromise your body and prevent it from fighting it off as it otherwise would if you hadn't taken the vaccine.
Anyway about fasting and taking the vaccine. I would not recommend fasting. Fasting puts a lot of strain on your body and so does the vaccine. I would fear what the combination of both could do to you.