Here you have a really nice explanation about bacteria, virus and how cells in our body are affected by them.
What’s a vaccination… Check this video and you will understand better.
Why do you think we have to treat and kill some bacteria in the milk berore packing it. This is the uperisation processs. Uperization is a method of sterilizing milk by injecting steam under pressure to raise the temperature to 150 °C. The added water is evaporated off.
If you want to know a little bit more about uperisation, or different ways to kill bacteria on the milk follow this link. It’s in spanish.
DIFERENCIAS ENTRE LECHE UHT, UPERISADA, PASTEURIZADA Y ESTERILIZADA