COVID-19 vaccine
The adenovirus is the virus that causes the common cold. It does not harm the human body much. Scientists have used the adenovirus in vaccines for many years against many diseases. Scientists take pieces of dangerous viruses and attach them to adenovirus to then inject the adenovirus into the human body. The human immune system learns to recognize the pieces of dangerous viruses. After, it can fight off the real dangerous viruses if the human is ever exposed to them.