Designing a vaccine starts with finding the right ingredients. Every infectious agent has molecules, called antigens, that the immune system could potentially recognize and attack. So scientists must carefully consider which antigens should go into a vaccine.
Scientists know a lot about how to design vaccines, but there are many diseases that haven’t been controlled through vaccination. HIV, for example, mutates quickly and is very good at hiding from the immune system, so it is hard for scientists to figure out which antigens to include in a vaccine.
