The underperformance of orally administered enteric vaccines in developing countries was the main topic of discussion today, the last day of the conference. In principle, this underperformance can be addressed by delivering vaccines through different routes. However, conventional intramuscular or subcutaneous immunizations often only induce weak immune responses in the gut where the infection occurs, and therefore protect only weakly against enteropathogens on the mucosal surface.
One question that keeps coming up at the meeting here is the paradox that compared with developed countries, some oral vaccines are less efficient in malnourished children in developing countries, even though such children show an overstimulation of their immune system in the gut.
Bacterial infections of the gut are one reason children in the developing world are malnourished, and malnourishment can lead to a poorer response to oral vaccines. One way to protect from the effects of such infections is to add probiotic bacteria to food, but scientists are just beginning to learn how such bacteria actually protect. Today, Shinji Fukuda from the RIKEN Institute in Yokohama, Japan, reported that he and his colleagues showed how a certain type of probiotic bacteria called Bifidobacterium that can be found in yoghurt can protect mice from dying from an otherwise lethal Escherichia coli (E. coli) infection (Nature 469, 543, 2011).
A healthy gut and good nutrition are important for a healthy immune system and a good immune response to vaccination, so it is not surprising that vaccines have been found to be less efficient in malnourished children. Still, “surprisingly little” is known about the impact nutrition has on the mucosal immune system of the digestive tract, according to the organizers of the Keystone Symposium on Malnutrition, Gut-Microbial Interactions and Mucosal Immunity to Vaccines, which is taking place in New Delhi Nov. 7-11. The meeting focuses on the role nutrition plays in gut immunity, knowledge of which could lead to the development of better vaccines for malnourished children.
Several speakers today discussed the development of new adjuvants, and Norman Baylor of the US Food and Drug Administration (FDA) gave an overview of the FDA’s safety and other regulatory requirements for adjuvants to be licensed for use in humans. “The biggest concern is safety,” he said. “That’s what we really need to demonstrate with these new adjuvants.”