Medical Corner: Smallpox Defenders

Smallpox is a disease that, in its natural form, has been eliminated from the world through the use of vaccine that made most of us immune. Without a population to infect, the disease stopped occurring in nature.

Now the U.S. government warns that this dread disease might reappear, this time as a weapon of mass destruction. The defense against smallpox is the same vaccine used to eliminate the naturally occurring version. It uses a live virus called vaccinia that triggers our bodies to produce protective antibodies with only minimal discomfort. The military has plans to immunize troops using vaccinia, and civil authorities are planning to offer this vaccination to the general public within a year.

The re-introduction of smallpox immunization is confronting the public with terms for which we have had little use for more than 25 years. A bifurcated needle, rather than the usual hypodermic needle, is used for the inoculation. A successful inoculation is called a "take." A take results in a skin lesion that progresses from a blister two to four days after inoculation to a healed ulcer covered by a scab that appears at 21 days. The vaccine provides a high level of protection from smallpox for three years. It then wanes. After 10 years, revaccination is necessary.

The public discussion appears to involve only health professionals and scientists who are familiar with the sciences of virology and immunology. Aircraft maintainers might conclude that the success of the smallpox immunization program depends on the skills of the medical practitioners and researchers. But the public discussion makes a big assumption. For the vaccine to produce immunity, the vials of vaccinia must arrive in the medical offices without any loss of potency. This assumption has failed many times. In fact, the World Health Organization estimates that 60 percent of vaccines reach their destination with some compromise in their potency.

Shipping vaccines from the pharmaceutical manufacturer to the medical office requires maintenance of a "cold chain" that encompasses all the procedures needed to maintain a biological product at its required temperature from the time of manufacture until it reaches the end user. The smallpox vaccine must be kept between 36 to 46 degrees F. The cold chain depends on adequate refrigeration and precision temperature control. These are technologies that are common in aircraft. Rapid shipment, an essential component in cold chain management, uses air carriers. Cold chain management–with the emphasis on refrigeration, precise temperature control, and air transportation–can easily require the skills of the aviation maintainer.

At this time, the military has the most experience administering the vaccine and managing its cold chain. The U.S. Army Medical Materiel Agency, which coordinated the distribution of vaccine to military units, developed specific procedures and equipment for cold-chain management. Of most interest to the maintainer is the equipment used for maintaining constant temperature. Called a VaxiCool, this device is a commercially available, high-efficiency refrigerator system. Its components include the lid, battery/storage box, compressor and condenser, power input panel, and carrying handle. It uses two 12-volt, 14-amp dry gel-cell batteries. When they are fully charged, the VaxiCool can maintain temperature for up to six days. Keeping the lid closed adds another 16 to 24 hours of constant temperature. It also can use AC power of 90 to 270 volts and power from a car battery/cigarette lighter.

Also within the shipping container is a monitor that records the temperature of the vaccine. Its red light indicates the shipment has exceeded temperature limits. The green light indicates it is within the limits. The end user must review this before administering the vaccine.

With knowledge of the shipping equipment, the aircraft maintainer could easily become the most critical person in the success of a community’s smallpox vaccination program. Imagine a scenario in which the maintainer receives a request to look at a shipping container. The first step is to recognize that the vaccine, like many other biologic products, is very temperature sensitive. Both time and temperature are critical elements in cold chain management. Next, be sure to read the material on the container. Vaccine shipped by the Army has extensive documentation, with appropriate telephone numbers for assistance. The assumption is that civil authorities will ship vaccine using a similar system.

An aircraft maintainer may be requested to troubleshoot the refrigeration system. Something as simple as plugging in accessory power may restore refrigeration, thereby saving an entire shipment.

A smallpox vaccination program is a complicated undertaking. Its success may at first appear to depend on knowledge of the biologic sciences, but the most critical issue is shipment. Shipping container refrigerator systems, like any mechanical system, can require maintenance. The aircraft maintainer has the skills that can save an entire shipment of this needed vaccine from becoming compromised.