Let’s do a thought experiment:
Think of every person you interact with on an ordinary day. Every person whose hand you shake. Every person you hug. The people you live with and work with. Then try to imagine every person these people interact with. Every person you meet is a person you could pass an infectious disease to. Every person you meet could pass an infectious disease to you.
Granted, this depends on how infectious the disease is and how the infectious disease spreads, and there are many ways this can happen. But for our purposes let’s stick to the flu. According to the CDC, “[p]eople with flu can spread it to others up to about 6 feet away.”
If you have the flu, and your coworkers and family members are vulnerable, you can spread the flu to them. They in turn can spread it to their coworkers and family members. But if one of your coworkers has gotten the flu vaccine, your colleague may be immune and your coworker won’t pass the flu along.
Now imagine every one of your coworkers has received the yearly flu vaccine. Even though you have the flu, they will likely not pass it on to their not-yet-vaccinated family members. In other words…