Earlier this year, California passed a state law banning vaccines containing thimerosal from being injected in pregnant women and children under 3 years old, but reports of flu shot shortages have temporarily overruled the law.
The exemption applies only to children under 3, and will last six weeks to give the pediatric vaccine maker -- Pennsylvania-based Sanofi Pasteur -- enough time to ship an additional half million doses.
"We feel it is important to offer this short-term alternative to parents and health care providers in order to ensure young children are protected from the potentially severe effects of the flu," said Kim Belshe, secretary of the California Health and Human Services Agency, in a statement.
Dr. Randy Bergen, a pediatric infectious disease specialist at Kaiser Permanente, said young children and the elderly are most vulnerable to seriously complications from influenza, and children under 3 who are getting their first flu shots will actually need two doses to receive full benefits.
The mercury preservative thimerosal -- which is roughly 50 percent mercury by weight -- has been used in U.S. vaccines since the 1930s to help prevent fungal and bacterial contamination. However, in the 1990s parents and physicians brought awareness to thimerosal's possible link to rising child autism rates.
Last year, anti-thimerosal lobbying groups successfully banned vaccines containing the preservative from being given to young children and pregnant women. However, the law can be waived if mercury-free vaccines are in short supply.
Four California medical groups -- the California branch of the American Academy of Pediatrics, the California Medical Association, the California Academy of Family Physicians and Kaiser Permanente -- recently asked the state to temporarily waive the law after some clinics reported running short of the mercury-free kids' vaccine.