It is well documented that breastfeeding protects full-term newborns and also older babies against infectious diseases such as meningitis caused by bacteria haemophilus influenzae. There have been a few studies comparing infants who were being fed human milk with infants who were on formula. These studies showed that meningitis and sepsis occurred more frequently in those infants who were NOT breastfed. One of the studies can be accessed here; http://www.ncbi.nlm.nih.gov/pubmed/10195681
Many mums understand that breastfeeding is best for them and their babies. However, it is probably even more important to provide young infants with human milk as their main feed who were born prematurely and/or suffer from very low birth weight. There has been an interesting study relating to human milk feedings and infection among very low birth weight infants.
The study showed that the incidence of infection (human milk [29.3%] vs formula [47.2%]) and sepsis/meningitis (human milk [19.5%] vs formula [32.6%]) differed significantly by type of feeding.
The incidence of any infection and sepsis/meningitis are significantly reduced in breast milk-fed premature infants compared with exclusively formula-fed premature infants. This study can be found here; http://www.ncbi.nlm.nih.gov/pubmed/9724686
It may not be easy to breastfeed a premature baby because many of them do not have the feeding skills such as the ability to latch on and suck. However, to give the baby the best immunological protection right from the start, expressing own breast milk should be considered. This is often better than putting the baby straight on to formula.