If we are ever reinfected by that same pathogen that contains that same antigen, we have these memory b cells that can now initiate a very quick and a very rapid response. And we actually won't feel the same exact effect that we felt the first time when we were infected by that pathogen. So the process of active immunity is a process in which our body develops immunity, these memory cells to the pathogen by being directly exposed to our antigens. For example, people who are exposed to chickenpox gain active immunity and will be very unlikely to ever feel that same effect they felt the first time when they were exposed. Now, there are two processes by which we can gain active immunity. What we just discussed a moment ago is a natural process.