Today, it's unusual for babies and children in the United States to die of pneumonia. But pneumonia still kills many young children in developing countries, in part because their bodies don't always respond effectively to anti-pneumonia vaccines.
New research suggests that a specific change in prenatal care for pregnant women in developing countries may improve their babies' vaccine responsiveness after birth. The work, published in PLOS Neglected Tropical Diseases, is a collaboration between Stanford pediatric infectious disease expert Desiree LaBeaud, MD, and colleagues at the School of Medicine, Lucile Packard Children's Hospital Stanford, Case Western Reserve University and the Technical University of Mombasa in Kenya. The team's findings offer an interesting example of the complex interactions between the maternal and fetal immune systems during pregnancy.
Some background: In recent years, the World Health Organization has expanded the use of childhood vaccines against the two bacterial species responsible for most pediatric pneumonia deaths, Streptococcus pneumonia and Haemophilus influenza type B (Hib).
LaBeaud and her colleagues previously found that when a mother is infected with parasites during pregnancy, her baby doesn't respond as effectively to these antibacterial vaccinations in infancy. In a group of 450 Kenyan women who gave birth between 2006 and 2009, 79 percent had parasitic infections during pregnancy, including malaria, schistosomiasis, lymphatic filariasis and intestinal helminths. Babies born to parasite-infected mothers had weaker immune responses -- specifically, lower levels of protective IgG antibodies -- after receiving antibacterial vaccinations in infancy.
"These effects appeared to be due to an 'imprinting' phenomenon" that skewed the baby's immune response to parasite antigens, the scientists wrote in the introduction to their new study. They proposed that this imprinting -- a phenomenon where the first pathogen an immune system encounters shapes its response to subsequent invaders -- might, in turn, affect how a baby responds to vaccines.
In the new study, the scientists monitored another group of 576 women who lived in rural Kenya and were pregnant between 2013 and 2015. The mothers were tested for eight different parasitic infections; 75 percent had at least one such infection during pregnancy, with malaria the most common. These pregnant women received more aggressive anti-parasitic therapy than the women in the previous study because prenatal care standards in Kenya had changed in the interim.
The babies in the new cohort had stronger immune responses to their infant vaccinations than babies in the earlier study. It's impossible to say for sure whether this was due to the stepped-up anti-parasite treatments in pregnancy, the scientists note, since they did not measure possible confounding factors such as mothers' nutritional status or parasitic infection severity. But, given that medications for parasites have been shown to be safe and effective during pregnancy, efforts to provide these treatments during pregnancy should be increased, they conclude.
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