I am insanely curious as to your background with your intense emotions about this.
Babies continue to have antibodies that were transmitted trans-placentally until like 18 months of age (this has ramifications for checking for some infectious diseases in infants). Yes, the IgA they get through breastmilk can help them fend off some illnesses and ideally every baby should be breastfed for at least a year, but that doesn't always happen for a variety of reasons (inability to store breastmilk, needing to go back to work, not having support at work to pump, difficulty producing, etc). And babies do eventually develop their own immune system--there would be no reason to give them vaccines so early if they did not respond to them at all, and most all people have sufficient titers against Hep B after the third dose, even if it was done at 6 months of age....
And 'finding a proper substitute' can be very dangerous in this day. Supposed 'breastmilk' that you can buy on ebay and elsewhere is often laced with cow's milk, and donor milk banks are few and far between in the US (I'm fortunate to train at an institution with one, and the response to opening the bank a couple years ago was so overwhelming that we're looking to start selling it outpatient, but it is far more expensive than formula).
The recommendation is to give breastmilk or formula through 1 year of age (I assume this is what
@Dr. Death was intending to say since formula is bottle feeding...). Then you can switch to cow's milk (whole milk). You can start feeding other things between 4 and 6 months of age, but up until 6-8 months, formula or breastmilk should be providing most of the nutrition in the infant's diet. Not sure where you are getting your information...