Breastfeeding may protect babies from post-vaccine fevers, according to a new study in the journal Pediatrics.

It’s not uncommon for an infant’s temperature to climb soon after immunization, Dr. Alfredo Pisacane of Universita Federico II in Napoli, Italy, and his colleagues note.

“Immunization is something like a ‘mild’ disease,” Pisacane explained via email, “and the immune system responds with local (pain, redness, swelling) and systemic (fever, decreased appetite) reactions.”

Babies will receive three rounds of shots during their first year of life, he added. “Post-vaccination fever is usually mild and of short duration. Nonetheless, 1-2% of infants can have high fever, which can represent a stress for them and their families.”

Breast and bottle-fed babies are known to respond differently to vaccines and to illness, Pisacane and his team explain, so they decided to investigate whether breastfeeding might protect against fever after a shot by having 450 moms keep track of their baby’s temperature for a few days after immunization.

Once babies had received the first or second set of two combination vaccines (against diphtheria, tetanus, pertussis, hepatitis B, polio, Haemophilis influenzae type b, and pneumococcal infection), mothers took the infant’s rectal temperature that evening and daily for three more days.

One hundred twenty infants were exclusively breastfed at the time of immunization, 154 were partially breastfed, and 176 were bottle-fed. Babies receiving the vaccine for the first time were about three months old, on average; those having their second set of shots were about six months old.

One-quarter of the exclusively breastfed babies, 31 percent of the partially breastfed babies, and 53 percent of the bottle-fed babies developed fevers of at least 38 degrees Celsius (100.4 degrees Fahrenheit) after being immunized, Pisacane and his team found.

For 90 percent of the entire group, fever occurred in the first day after immunization; three-quarters had fevers lasting just one day. Just eight of the infants - four partially breastfed, and four not breastfed - had fevers above 39 degrees Celsius (just above 102 degrees Fahrenheit).

Risk of fever for the breastfed babies was 54 percent lower than for the bottle-fed babies, while partially breastfed babies were at 42 percent lower risk. The apparent protective effect of breastfeeding remained even after the researchers accounted for factors like mother’s education and the number of other children in the home.

Breast milk could reduce the production of inflammation-promoting proteins released after immunization, the researchers note, while breastfeeding itself could also comfort feverish children and encourage them to eat. Pisacane and his team point out that bottle-fed babies have been reported to consume fewer calories after immunization than breastfed babies do.

“When infants are sick and after a vaccination shot, they need not only water, food and a calm environment, but also to be protected,” Pisacane told Reuters Health. “They need the warm body of their mothers. Breastfeeding provides all what an infant does need during illness.”

He added, “Also, partial breastfeeding is useful to protect infant health and to ensure a warm relationship between a mother and her infant.”

SOURCE:  Pediatrics, online May 17, 2010.