A Bouncer at the Door
The chief target of noninjected vaccines is the body’s vast expanse of mucosal membranes. Combined, mucous cells cover an area equal to about one and one-half tennis courts, lining the respiratory and gastrointestinal tracts, urinary and genital passages-even the eyelids. Mucosal immunity is the body’s front line of defense, since 90 percent of infections start at mucosal sites. Such common infections as pneumonia, sore throats, flu, diarrheal diseases, ulcers and sexually transmitted diseases all begin at mucosal surfaces.
Mucosal immunization prompts the immune system to produce two types of antibodies in different regions of the body: powerful IgA antibodies at mucosal surfaces, and IgG antibodies in the bloodstream. In contrast, injected vaccines trigger only IgG antibodies in the blood. By eliciting the IgA response, mucosal vaccines protect the body against invading pathogens before they reach and damage internal organs. The protection of an IgG-inducing injected vaccine only kicks in after an infection starts.
A mucosal vaccine could take a number of different forms. Nasal sprays, nose or eye drops, capsules, liquids and rectal or vaginal suppositories are all possible vehicles for vaccination-some clearly more practical and palatable than others. Fortunately, says David Burt, vice president of research at Montreal-based Intellivax International Inc., “the mucosal immune system is interconnected,” so vaccines applied at a convenient mucosal site protect other areas of the body as well.
A Shot in the Nose
One of the first vaccines to make it into patients’ nostrils will probably be FluMist, a nasal spray aimed at influenza viruses. Both children and healthy adults may soon get their annual flu “shots” from this syringe-like device with an aerosol sprayer where the needle ought to be. The device delivers a live, but weakened, influenza virus that only grows at the cooler temperatures of the nasal passages. There, the vaccine primes the mucosal immune system to stop disease-causing flu viruses before they can take hold in the nose and upper airways.
FluMist has done well in clinical trials-it provides 93 percent protection against the flu in children, with mild side effects (runny nose or sore throat) that last a day or so. But the new vaccine might also have another-and more positive-side effect. It reduces the rate of flu-related ear infections by 98 percent. Ear infections send American children to the pediatrician more than 31 million times each year, and most of those kids receive antibiotics; vaccinating children against influenza could make a dent in this overuse of antibiotics and the resulting rise of drug-resistant bacteria.
Aviron, the California company that is developing FluMist, applied for FDA approval for the nasal flu shot this summer. The company hopes to make FluMist available in time for the 1999 flu season.