Inhalant Measles Vaccine Could Save Thousands of Lives

A dry-powder, inhalable, needle-free vaccine has been designed for developing countries, where lack of clean water, sterile needles, and electricity for refrigeration hinder the administration of traditional liquid vaccines.

Researchers from the University of Colorado (Boulder, USA) developed the inhalable form of the vaccine using a patented process known as carbon dioxide-assisted nebulization with a bubble dryer (CAN-BD). In this process, the weakened vaccine, dissolved in water or an alcohol (or both), is mixed intimately with near-critical or supercritical CO2 by pumping both fluids through a low volume tee-valve to generate microbubbles and microdroplets, which are then decompressed into a low-temperature drying chamber, where the aerosol plume dries in seconds.

The process allows the particles to be scaled in the 3-5 µm size range (suitable for lung delivery), without destroying biologic activity. The dried and micronized vaccine is maintained throughout the process at near ambient conditions, thus retaining its bioactivity. The CAN-BD process has been shown to successfully produce stabile dry powders that have passed the World Health Organization (WHO) stability test for one week at an ambient temperature of 37 ^oC.

The researchers are now are working on an inexpensive dry powder inhaler that would deliver measles (or alternatively influenza) vaccines to developing nations. In replacing the injection method of vaccination delivery, the new method also would help reach those who refuse inoculations because of their fear of needles. Human clinical trials are expected to begin in India in 2010, after animal safety studies are completed by the end of 2009. The researchers claim that the vaccine could be produced for about US$0.26 per dose. The study was presented at the 238th national meeting of the American Chemical Society (ACS), held during August 2009 in Washington (DC, USA).

"Childhood vaccines that can be inhaled and delivered directly to mucosal surfaces have the potential to offer significant advantages over injection,” said lead author Robert Sievers, Ph.D., of the center for pharmaceutical biotechnology. "Not only might they reduce the risk of infection from HIV, hepatitis, and other serious diseases due to unsterilized needles, they may prove more effective against disease.”

Supercritical carbon dioxide refers to carbon dioxide that is in a fluid state while also being at or above both its critical temperature and pressure. Carbon dioxide usually behaves as a gas in air at or as a solid called dry ice when frozen. If the temperature and pressure are both increased to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid. More specifically, it behaves as a supercritical fluid above its critical temperature (31.1 °C) and critical pressure (7.39 MPa), expanding to fill its container like a gas but with a density like that of a liquid. Supercritical CO2 is becoming an important commercial and industrial solvent due to its role in chemical extraction in addition to its low toxicity and environmental impact. The relatively low temperature of the process and the stability of CO2 also allow most compounds to be extracted with little damage or denaturing.

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