If most or all vaccines now administered parenterally could be administered orally, the implications for public health would be far-reaching. The availability of an oral vaccine against the pathologic agents of these diseases would result in increased numbers of children being vaccinated. At least that would be the expected consequence of decreasing the cost of the vaccine and the number of health care professionals needed to administer it. There would likely be other benefits as well, not the least of which would be a reduction in spent needles, syringes, and other medical waste. The single largest impediment to development of oral vaccines has been finding a way to get antigenic molecules out of the gut and into the circulation.
Botulinum toxin is a large molecule with multiple functional domains.
The structural elements responsible for cross-membrane transport are clearly separate from those responsible for nerve poisoning. If the toxic domain were removed, the antigenic portion of another molecule might be substituted. In other words, a nontoxic fragment of botulinum toxin might be enlisted as a chauffeur to escort vaccines from the gut to the blood stream. This hypothesis is now undergoing rigorous experimental evaluation. Even though it is too early to know with certainty whether botulinum toxin, or an agent modeled after the toxin, is the long-sought carrier for oral vaccines, no one should be surprised if that should turn out to be the case.