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.

A possible explanation was mentioned today by Per Brandtzaeg of the University of Oslo who gave an overview of the human intestinal immune system. He said that malnourished children in developing countries may have too many regulatory T cells (or Tregs), which may explain why their immune response to oral vaccines is suppressed.

All of the licensed influenza vaccines and most of the candidates in clinical or pre-clinical development target the hemagluttinen (HA) antigen on the surface of the virus. This is partly because induction of antibodies against HA is a correlate of immune-mediated protection against influenza, making the surface protein a logical target for the production and quality assessment of vaccines.

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).

For the past 50 years, vaccine manufacturers in the United States have used egg-based technology to develop the seasonal influenza vaccine, and they might have stuck to this method were it not for the emergence of the H5N1 virus in Asia. Since its appearance in the mid-1990s, the highly pathogenic strain of influenza, which jumped directly from birds to humans, has resulted in 500 cases and 300 deaths.

In today’s morning session, it was interesting to hear that compared with children in developed countries, children in the developing world show a poorer response to oral vaccines (such as 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.

A healthy gut and good nutrition are important for a healthy immune system and a good immune response to vaccination, so it's 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 for gut immunity, knowledge of which could lead to the development of better vaccines in malnourished children.