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. So active immunity can be achieved either naturally through some type of exposure to that pathogen, for example, an infection, which is what we discussed earlier or we can actually induce active immunity artificially via process known as immunization. And immunization involves injecting something called vaccines into our body so what exactly is a vaccine? So, a vaccine is essentially this little test tube that contains some sort of pathogen inside that test tube.