When we read about deadly infectious diseases, we often feel life is unfair. After all, why can’t our body fight of the invading microorganisms and keep us safe? In reality, however, our body possesses amazing defense capabilities: our immune system routinely protects us from a vast army of pathogens—the organisms that can cause diseases. While our immune system excels at eliminating a previously-encountered pathogen, it also tries its best when it does encounter a novel pathogen. In this essay, I will provide a brief overview of how our immune system works and how it relates to vaccine development.1 Elimination of pathogens (Courtesy: https://www.britannica.com/ ) Our immune system can be broadly classified into two systems: the innate/general resistance system and the adaptive system. The innate system may be able to eliminate a pathogen on its own or it can stimulate the adaptive immune system to become involved in eliminating the pathogen. Let’s see how the innate/general resist