The “flu shot” could one day be a thing of the past, replaced by the “flu sniff.”

Alternative ways of delivering vaccines, either by inhaling, swallowing or eating them, could prove to be better at targeting certain parts of the body – and less likely to strike fear into the hearts of children (and skittish adults) than injections. And when you want to protect against respiratory illnesses, why not go straight to the source of the problem?

In a recent paper appearing in the Journal of Aerosol Medicine and Pulmonary Drug Delivery, Dutch researchers from the University of Groningen and the National Institute for Public Health and the Environment outlined the state of the research on inhaled vaccines.

“The lung is an immunologic powerhouse that remains largely unexplored,” Gerald C. Smaldone, the editor-in-chief of the Journal of Aerosol Medicine and Pulmonary Drug Delivery said in a statement Monday. “Theoretically we should be able to avoid needles and simply inhale our vaccines."

Vaccines delivered through the lungs have been attracting more attention from researchers of late because it seems that they can kickstart immune activity right at the common entry point for lots of pathogens, including the bacteria that cause pneumonia. The lungs are specially equipped to become a pathogen-fighting battlefield, with large surface areas and hordes of specialized cells ready to swarm at a moment’s notice.

Pulmonary vaccines can be delivered via liquid aerosol or dry powder aerosol. Dry powder aerosols are made up of smaller particles than the liquid aerosols, and preliminary research shows that smaller particles lead to deeper penetration of the lung. Some inhaled vaccines in development target specific areas in the lung, while others are formulated to induce specific immune cells. Research in animals also suggests that where the vaccine agent is deposited in the lungs can affect the immune response generated, according to the authors.

There have only been a few clinical studies of pulmonary vaccines in humans, mostly focused on an inhalable measles vaccine.

But “despite the numerous clinical trials that have been performed on pulmonary vaccination with nebulized measles vaccine, no final conclusion can be drawn. The results of these clinical trials are often contradictory,” the authors wrote.

One problem is that the measles vaccine is highly unstable, and many trials have not monitored how it loses its potency through the process of being transformed into an aerosol. Still, the inhaled measles vaccine is likely to have advantages over injection and be especially effective as a booster vaccination, the authors say.

Since pulmonary vaccines are still in their infancy, the data on safety is still somewhat limited, and larger clinical trials are needed.

So for the meantime, be prepared to roll up your sleeve and face the needle.

SOURCE: Tonnis et al., “Pulmonary Vaccine Delivery: A Realistic Approach?” Journal of Aerosol Medicine and Pulmonary Drug Delivery 25: 249-260, October 2012.