system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we vaccinate people instead of injecting them directly with antibodies? Is there a particular reason people need to generate the antibodies themselves?
gpt
Antibodies are proteins that will eventually degrade. You could get regular antibody infusions but they would not last as long as having your own immune cells to produce them as needed (which you get from a vaccine). Immune cells can last decades, even entire lifetimes, antibodies last weeks to months at best. 

There is more to the immune system than just antibodies. Vaccines can also activate immune cells called T cells which have many important roles. There are different types of antibodies, with different roles, including antibodies in the mucus membranes which you would not get from an infusion. Additionally, the cells that make antibodies can make better antibodies with each exposure, selecting variants of antibodies that bind antigens best (which is important when the antigens themselves are also changing). 

So yes you could give antibodies, and in some cases we do give antibodies, but vaccines are generally going to be much better.