The finding comes from a study of babies in Buenos Aires, Argentina, by Dr. Fernando Polack, from Vanderbilt University in Nashville, Tennessee, and colleagues.
Boys may derive some protection from breastfeeding, noted Polack, but this study may have been too small to sufficiently identify this benefit.
Still, the results mirror previous research conducted in Argentina and the United States, Polack said, and when taken together indicate that "mothers of girls should pay close attention to the importance of breastfeeding to protect their infant's lungs."
The investigators assessed how breastfeeding altered the risk for pneumonia and hospitalisation among 323 infants who developed an acute respiratory infection at an average age of 4.6 months.
Overall, 77% of the infants were breastfed, Polack's team reports in the Pediatric Infectious Disease Journal.
Viral pneumonia developed in 23% of the formula-fed girls versus 5% of the breastfed girls. Hospitalisation was necessary more frequently among formula-fed girls (38%) compared with breastfed girls (18%).
These associations held after taking onto account other risk factors for respiratory infection such as tobacco use at home, siblings 10 years old and younger, living in a crowded environment, age younger than 3 months, the presence of other viral infections, and a history of asthma among family members.
Any benefit for boys, on the other hand, was not significant from a statistical standpoint in this study.
Polack's group calls for larger studies in different ethnic groups to investigate how breastfeeding impacts girls and boys. They also suggest aggressive promotion of exclusive breastfeeding, as well as active monitoring of non-breastfed girls.
Do you believe that "breast is best"? Would you recommend breastfeeding over bottle feeding babies?