A Shot in Time; the Technology Behind New Vaccines

Article excerpt

Infectious diseases have revaged the world's population for thousands of years. Prevention has a shorter history. In the 10th century B.C., the Chinese documented the practice of injecting pus from the smallpox pustules of a sick person into a cut on the hand of a healthy person. This induced form of smallpox was often less deadly -- though no less infectious -- than the original.

In 1796, English physician Edward Jenner noticed that dairymaids who caught cowpox -- a similar disease found in cows -- did not develop the more disfiguring, deadly smallpox. He soon developed the first safe, practical, preventive vaccine (from the Latin vacca, or cow) for smallpox and predicted the eradication of the would take 180 years: The last case of wild smallpox was reported in Somalia in 1977.

Today, vaccines are among the safest, most cost-effective, and powerful tools for preventing disease. In 1990, the World Health Organization's Expanded Program on Immunization (EPI) reported that 80 percent of the world's children were immunized against measles, diphtheria, pertussis (whooping cough), tetanus, tuberculosis, and polio. Just 20 years ago, when the program started, less than 5 percent of children were fully immunized.

The very success of EPI carries the germ of failure. Because some infectious diseases have become so rare, parents in developed countries often neglect to take their children in time after time for vaccinations and booster shots: Complete immunization in the United States calls for a total of 17 shots and six visits in the first 15 months of life.

Although some 87 percent of U.S. children are fully immunized by the time they enter school, at age 2 only about 44 percent have received their full course of vaccinations. In the developing world, too, reaching children with additional doses poses a substantial problem.

Twenty percent of the world's children remain unimmunized. "Between 6 and 8 million children a year die of diseases that are theoretically preventable if we could either deliver the vaccines we have or make new vaccines to prevent these [infectious] diseases," says Col. Jerald C. Sadoff, director of the Division of Communicable Diseases and Immunology at the Walter Reed Army Institute of Research in Washington, D.C.

So researchers seek a 21st century "magic bullet." Working with a number of experimental techniques, they envision successfully developing a safe, effective, single-dose vaccine, given at birth, that can protect the world's children against a host of deadly ailments.

In 1990, the World Health Organization, the United Nations Children's Fund, the United Nations Development Fund, the Rockefeller Foundation, and the World Bank sponsored the Children's Vaccine Initiative (CVI) to pursue this goal.

The CVI wants to move technologies for new or better vaccines from the laboratory bench to the bush. It seeks affordable vaccines that require fewer doses, can be given earlier in life, can be combined in novel ways (reducing the number of shots and visits required), remain stable at tropical temperatures (reducing dependence on refrigeration), and are effective against new diseases.

"There's not a single aspect of this that would require a quantum leap in information or knowledge that we can see," says William H. Foege, director of the Task Force for Child Survival and Development at the Carter Center in Atlanta. "The question is whether we have the tenacity to go after it."

Vaccines mimic the organisms that causes disease, alerting the immune system that certain viruses or bacteria are enemy agents. Because of this advance warning system, when the "real" organism invades the body, the immune system can marshal a response before the disease has time to develop.

Ideally, the body will both make antibodies that bind to and disable the foreign invader (humoral immunity) and trigger white blood cells called T cells to attack cells in the body taken over by viruses (cellular immunity). …