As the stock of influenza vaccine is quickly declining in the United States, the Centers for Disease Control and Prevention (CDC) has indicated that those in the most vulnerable age ranges--especially those over the age of 50 years and children between the ages of six months and 23 months, children and adults with chronic ailments like heart disease, and pregnant women--should take priority in getting flu shots. The CDC did not make a full recommendation about which patients should get the vaccine, so individual physicians and clinics are permitted to make that choice themselves. They do not face an easy decision, however; pediatricians, for example, are unsure whether to give the vaccine to first-time recipients, who then need a booster shot after 30 days, or to vaccinate children who have already received a flu vaccine in the past and therefore only require one shot. Meanwhile, the CDC is trying to figure out how much vaccine is really left, with estimates as low as a two-week supply and 200,000 doses left out of 83 million distributed nationwide.