1. Aylward, B., Lloyd, J., Zaffran, M., McNair-Scott, R. & Evans, P. Reducing the risk of unsafe injections in immunization programmes: financial and operational implications of various injection technologies. Bull. World Health Org. 73, 531–540 (1995).
2. Simonsen, L., Kane, A., Lloyd, J., Zaffran, M. & Kane, M. Unsafe injections in the developing world and transmission of bloodborne pathogens: a review. Bull. World Health Org. 77, 789–800 (1999).
3. Levine, M.M. & Dougan, G. Optimism over vaccines administered via mucosal surfaces. Lancet 351, 1375–1376 (1998).
4. Neutra, M.R., Frey, A. & Kraehenbuhl, J.P. Epithelial M cells: gateways for mucosal infection and immunization. Cell 86, 345–348 (1996).
5. Levine, M.M. et al. Duration of efficacy of ty21a, attenuated Salmonella typhi live oral vaccine. Vaccine 17 (Suppl 2), S22–S27 (1999).