New Kind of Vaccine Raises Hopes

Vaccines are the most effective way to fight infectious diseases.They wiped smallpox off the planet, nearly eliminated childhoodkillers such as whooping cough and measles and dramatically reducedhepatitis and tetanus in adults.

But conventional vaccines have many shortcomings. Poliovaccine, for example, sometimes causes the disease it is meant toprevent; the diphtheria-whooping cough-tetanus shot occasionallytriggers allergic reactions so severe that children suffer braindamage. And vaccines have failed to stop some of the graver threats,including tuberculosis, herpes and the human immunodeficiency virusthat causes AIDS.

Now a revolutionary new type of vaccine …