Down the Gullet
Another obvious route for noninjectable vaccines is-down the hatch. But oral vaccines face tough obstacles. They must survive the harsh environment of the stomach and intestines. In addition, the digestive tract sees a lot of “immunological challenges from food,” says Peter Nara, president of the International Society for Vaccines and director of R&D at the Maryland start-up Biological Mimetics. As a result, the lining of the tract tends to overlook immune stimuli such as vaccines. Any vaccine operating there is “working against City Hall,” according to Nara.
Despite these hurdles, new vaccines against diseases as disparate as typhoid fever and stomach cancer will soon be swallowed. One of the first will most likely be RotaShield, developed to protect young children from the severe diarrhea caused by rotaviruses. Nearly 1 million children die yearly from rotavirus infections in developing countries, and its oral form may make RotaShield easier to distribute in those regions. In the United States, 3 million cases of rotaviral diarrhea account annually for 500,000 doctor visits, 100,000 hospitalizations and 100 deaths, costing the health care system $1.4 billion in direct and indirect costs.
Albert Kapikian and his colleagues began tinkering with the oral rotavirus vaccine in 1980. “We never even considered the possibility of an injected route,” says Kapikian, head of the epidemiology section of the Laboratory of Infectious Diseases, part of the National Institute of Allergy and Infectious Diseases. Making an oral vaccine for an intestinal virus “was a natural way to go.”
To save the vaccine from destruction in the stomach’s acidic environment, children in early studies drank milk (an acid-neutralizer) a half-hour before vaccination. In its final form, the vaccine is freeze-dried, then mixed with a small amount of a salty buffer that protects it. In the gut, the virus multiplies long enough to generate protective mucosal antibodies-the only side effect is a mild, brief fever. “The proof is in the pudding-or the protection-which has been excellent,” says Kapikian; the vaccine reduces the incidence of severe rotaviral diarrhea by up to 90 percent. Licensed by Wyeth-Ayerst Laboratories, RotaShield is awaiting FDA approval. The vaccine, which will be recommended for all children at 2, 4 and 6 months of age, has already gained the endorsement of the Centers for Disease Control, the American Academy of Pediatrics, and the WHO.