The WHO isn't a great source for breast feeding, because of weird political and historical reasons.
In the 1960s, Nestle started pushing formula hard in developing countries in Africa. And by "pushing," I mean they hired people to dress as nurses and tell women that they should use formula because it was healthier than breast milk. They also gave women free samples, knowing that if they used the samples in the beginning, the women would have a hard time getting their milk to come in later, "hooking" them on the formula.
What made it worse is that the formula was very, very expensive to these people, and often didn't have any instructions printed in a language the mother could read (assuming they were even literate in any language), causing the formula to be routinely under-dosed. Oh, and they often didn't have access to safe drinking water, which is kind of important for formula.
We don't know how many babies died because of Nestle's actions, but it was probably in the millions.
This led to the huge Nestle formula boycott of the 70s. The WHO started pushing breast feeding hard, and created a whole panel to do it, made up of breast-feeding advocates who viewed it as a kind of panacea. That wouldn't have been a problem normally because strong believers in breastfeeding were probably needed to counteract the corporate push towards formula, but there was a big complication: AIDS. In 1981 the first cases of HIV transmission by breast milk were reported, and by the mid-80s, doctors knew for certain that HIV could be transmitted by breast feeding. But the breast-feeding advocates in the WHO wouldn't accept the facts. Even in the 90s the WHO was "debunking" that "myth" in their literature to third-world mothers.
We don't know how many babies died because the WHO told HIV-positive mothers that they should breast feed, but it was probably in the millions.
To this day, the WHO promotes breast-feeding heavily (which is fine, they should) but they play up the benefits of it more than is really scientifically defensible. Their breastfeeding outreach isn't run by impartial people, but by true-believers in the power of breastfeeding. So take their info with a grain of salt.