Advances in oral vaccine delivery options

Vaccines have been one of the most far-reaching and important public health initiatives of the 20th century. Yet as we move into the 21st century, millions of people still die from vaccine-preventable diseases such as measles and tetanus, and complex diseases, such as malaria and HIV, for which we have no vaccines. New vaccines that can be administered orally, are stable at ambient temperature, and can be produced cheaply, have the potential to transform health policy and practice in both developed and developing countries. Although oral delivery is the preferred route of administration, it is inefficient for the delivery of ‘naked’ antigens. Delivery of a vaccine via the oral route in a sufficient dose to induce a protective immune response depends on overcoming the loss of antigen integrity that occurs during intestinal passage. Several strategies have been employed to prevent this loss of antigen(icity) and improve the delivery of vaccinogens by the oral route. These include live vectors, transgenic plants, and particulate formulations such as microparticles, liposomes, and virus-like particles. Although many of these systems have progressed to clinical trials, the most promising results are seen where strategies are combined. Prime-boost schedules and combined technologies are likely to be a critical component of future oral vaccination schedules. Further technological breakthroughs may also be required before strong protective immune responses can be consistently induced in humans. Nonetheless, the potential of future oral vaccination strategies is readily apparent.