What is one part of a research plan that must be followed when developing a new vaccine?

When developing a new vaccine the researchers will need to find out which receptors play a role in the spread of a virus or bacteria, and look at the molecular shape.

Vaccines contain bacteria or viruses (microbes) either parts of wholes that have been killed or weakened so they don't causes diseases. These microbes work with the immune system to create antibodies against the bacteria or viruses. So if you are exposed say to Measles the body remembers these bacterias or viruses so the body is able to fight of the diseases quickly and you don't get sick.