While eating lunch at the local café, the pathogens of the COVID-19 virus that were on Scooter’s food entered his body, passing his first line of defence when he ate them. Due to this being a new virus, and he hasn’t had the vaccine, his immune system has had no previous exposure to it, and he is vulnerable to its effects.
The COVID-19 virus starts to reproduce using his cells, giving him some mild cold-like symptoms, indicating that his body has begun to fight it in the form of the non-specific defence mechanism. This is a general response to fight the pathogen and kill it.
Because the third line of defence doesn’t know the unique shape of the antigen yet, the virus can cause some problems to the body while the immune system finds the right antibody. As this happens, he spreads the virus to others.
Eventually Scooter’s immune system finds the right antibody and begins to produce B cells that help to fight it in the specific defence mechanism and memory B cells to help remember the virus in the case of secondary exposure and fight it more quickly. Scooter now has immunity but has spread the virus to hundreds of other people.
Memory B cell
Taylor, however, has already had the COVID-19 vaccine and has artificial immunity to the virus. The vaccine simply injects a weakened or dead coronavirus pathogen into her system, so that it does not begin to reproduce and cause any harm.
The third line of defence will still fight the pathogen though and produce memory B cells to remember the virus. When Scooter and Taylor meet up at a small party, Scooter passes the virus on to everyone there, but Taylor’s body remembers the pathogen and kills it before it causes any symptoms.