IOWA CITY, IA - AUGUST 11:  A syringe of the H1N1 vaccine, developed by CSL of Australia, is held at the University of Iowa Health Center during trial of the vaccine on August 11, 2009 in Iowa City, Iowa. The University of Iowa Health Center is one of 8 trial sites across the nation conducting human studies on the new vaccine which is looking at optimal dosage levels for a variety of age groups. Getty Images logo Getty Images 4 months ago

IOWA CITY, IA - AUGUST 11: A syringe of the H1N1 vaccine, developed by CSL of Australia, is held at the University of Iowa Health Center during trial of the vaccine on August 11, 2009 in Iowa City, Iowa. The University of Iowa Health Center is one of 8 trial sites across the nation conducting human studies on the new vaccine which is looking at optimal dosage levels for a variety of age groups.