Vaccine Responses in Children in Developing Countries

Compared with children in developed countries, children in the developing world show a poorer response to oral vaccines (such as oral polio vaccine), whereas their response to vaccines that are administered systemically by injection (such as measles vaccine) doesn’t appear to be much different.

William Petri from the University of Virginia reported on studies of the possible reasons for why these children respond so poorly to oral vaccination. He and his colleagues found that children with more stunted growth are most likely to fail to respond to oral vaccines, suggesting a possible role of malnutrition. The researchers also found that such children more often have antibodies against bacterial endotoxins. There is evidence that this might cause chronic inflammation in the gut, Petri said, coming from work by Evan Newell of Stanford University and colleagues who looked at peripheral blood mononuclear cells in three year old children who had received the oral polio vaccine in the first months of their life. They found that the children who didn’t respond to the vaccine had an elevated expression of inflammatory cytokines but were also less able to respond to cytokine stimulation.

This suggests that in the children who fail to respond to the oral polio vaccine, bacteria are leaking out of the gut and induce an overstimulation of the immune system, which paradoxically results in suppression of the response to the vaccine. “[It] supports this idea that chronic inflammation in children, perhaps through exposure to bacterial endotoxin in the gut, is causing these different immune cell populations to be non-responsive to cytokine stimulation,” Petri said.   

The leaky gut comes from a condition called tropical enteropathy, Petri said, where there is so much inflammation in the gut that the gut villi fuse together. It is thought to be caused by the onslaught of intestinal infections many children in the developing world are exposed to.