No more infections. No more hepatitis. No more pneumonia and influenza. No more venereal disease. No more children’s contagions. Good-bye to malaria, meningitis, and maybe, one day, the common cold.

Before the 20th century ends, science may bid good riddance to most, if not all, diseases caused by viruses and bacteria. Spurred by the successes of vaccine treatments over the past decades, biologists and chemists are creating amazing new vaccines that stop those germs invading and growing in our bodies.

What exactly is a vaccine? Simply put, a vaccine is a dose of just enough of a particular germ to trigger your immune system but not make you sick. Into each vaccine scientists put all or part of the particular germ against which they want to protect you, but first they weaken, dismember, or kill that germ in the laboratory. Once you swallow or take shots of this altered germ, the pieces tell your body to make anti-germ proteins called antibodies. The antibodies stave off the deadly germs from getting a foothold in your body.

Keep in mind that vaccines prevent infectious disease; they do not cure it. Scientists are using new technology to improve old vaccines, such as those in whooping cough and influenza, making them safer and more powerful. And they are fashioning new vaccines for diseases against which we have no protection. Vaccines for genital herpes and chicken pox, for example, are two of a dozen under development.

Elena Jenkins, 10, of Nutley, New Jersey, owes her life to the new, experimental chicken pox vaccine from Japan. Five years ago, she came down with leukemia, which doctors stopped with drugs and radiation. But, like all leukemia victims, Elena became acutely susceptible to chicken pox. In normal children, only a mild rash covers the skin; when the disease attacks a person who has had leukemia, it can kill horribly by peeling away all the skin and invading the brain.

Elena’s parents, Linda and Bob Jenkins, lived in dread that Elena would catch chicken pox. “We were afraid her brother would bring the disease home from school,” recalls Mrs. Jenkins.

In May 1981, Dr. Ann Gershon, then of New York University Medical Center in Manhattan injected Elena with the new vaccine, which is made from live, weakened viruses. A year later, Elena broke out in a mild case of chicken pox and survived.

Dr. Jonas Salk, who in 1955 invented the first vaccine that cut down the crippling polio virus, said that modern technology opens the way “to control more and more of the major infections and parasitic diseases.” That technology includes these developments:

•   Growing viruses and bacteria in test tubes to produce the raw material of vaccines

•   Altering the genes of viruses and bacteria so that they cannot produce disease but can stimulate antibodies

•   Isolating pieces of germs that can trigger immunity against the whole germ.

Before he died, Dr. Salk told me, “If there is a will to do so, there will be a way to develop vaccines.”

This scientific know-how was slow in coming. In 1796, Edward Jenner, an English doctor, observed that milkmaids who caught cowpox from cows did not catch the deadly smallpox. Dr. Jenner got the idea that rubbing pus from the cow’s pox into people’s skin might somehow protect them from smallpox. Thus began vaccination, which comes from the Latin word for cow, vacca.

Dr. Jenner didn’t know it, but the pus contained the cowpox virus, now called vaccinia. (Like all viruses, vaccinia is a tiny germ, so small that 100,000 of them can fit onto the period at the end of this sentence.) And because this cowpox virus is a weak “cousin” to the smallpox virus, the cowpox antibodies stopped the smallpox germ.

Much of vaccine technology today is based on Dr. Jenner’s principle – that is, using weak “relatives” or altered germs to fight more powerful viruses and bacteria.

However, most infections do not have such close “relatives” as do cowpox and smallpox, so scientists have to weaken strong viruses in the laboratory.

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