A national program to vaccinate 500,000 health care workers against smallpox got off to a slow start this week when only four people showed up. Connecticut officials had hoped to inoculate 20 doctors and nurses in front of television cameras on the first day, to inspire public confidence. But health care workers didnt show up, after the nurses union warned that Connecticutthe first state to begin inoculationshad rushed the program. The union said health care workers deserved more information about the possibility of severe side effects from the vaccination. President Bush ordered the inoculations so that nurses and doctors could treat people infected by a biological attack without falling ill themselves. Many health workers say they wont get the shots until the government guarantees compensation if the vaccine makes them sick.