Government health officials have recalled about 800,000 swine-flu shots for children after discovering that the vaccine has lost some of its potency. The shots, which were meant for children from ages six months to 3 years, were discovered to be less effective than they were at their initial testing but do not pose any danger to those who have already been vaccinated with them, according to officials. "No action is necessary by a parent of a child who received this vaccine," said a spokesman for the Centers for Disease Control and Prevention. The doses were distributed last month by Sanofi Pasteur, a French company that touts itself as the world's top manufacturer of flu vaccines. There is no official explanation for the change in the medication.