Blood already is safe.
But the new genetic technology, which should encompass all blood transfusions by September, promises to make it even safer. Some of the tests can detect as few as 10 copies of a viral gene. Viral genes spread through blood faster than the immune system begins forming antibodies to fight them, a reaction that may not occur until 20 to 80 days after the person is infected. Yet today's blood testing depends largely on tests that detect antibodies in an infected donor. So newly infected donors sometimes slip through.