The Food and Drug Administration approved the long-awaited chickenpox vaccine today, just in time for the spring outbreak of the disease. Varivax, produced by Merck & Co., has a 70 percent to 90 percent effectiveness rate. It is expected to be available in doctors' offices within eight weeks. Merck still has to study thousands of vaccinated patients to find out how long Varivax protects and whether booster shots will be needed. "People have been hoping for it for a long time," says TIME medicine writer Christine Gorman. "And while it is not 100 percent affective, it is better than nothing." Four million Americans get chicken pox every year. While most of them suffer relatively mild symptoms, about 90 people die, and 9,300 must be hospitalized.