With the U.S. Centers for Disease Control and Prevention hoping to have 120 million doses of H1N1 swine flu virus vaccine ready before flu season this fall, some are raising concerns over what they see as an effort to rush the drug through safety trials. The source of many of these concerns is the probability that the mercury-containing preservative thimerosal will be an ingredient in some of the doses of the new vaccine. Concern over thimerosal has lingered for years. Groups opposed to current vaccination practices continue to condemn thimerosal as a toxin responsible for the development of autism and related ailments in children. Additionally, the possibility that the swine flu vaccine could also contain an adjuvant, an ingredient that would allow more doses to be created from existing supplies of the vaccine, has also worried these groups. We don't have adequate safety studies on this vaccine before we are moving forward to market," said Lyn Redwood, president and co-founder of the group SafeMinds. "I'm really not convinced that we know for sure that the risk of the disease outweighs the risk of the vaccine, especially since this is a brand new additive that we have never used before in combination with thimerosal." During the 1976-77 flu season, a vaccine developed to prevent the spread of a strain of the swine flu was linked to an as-yet-unexplained increase in cases of a rare neurological condition known as Guillain-Barre syndrome in those who received immunizations.