Jim Carrey and Jenny McCarthy took part in the Green Hour Vaccines march on Washington D.C. The actors hope that by joining the march they could raise awareness about autism.

They joined with national autism advocacy groups to raise awareness about toxins in vaccines and to change children’s vaccination schedules.

The debate about the link between autism and childhood vaccinations has brought to light new worries about the hidden threat of vaccines. Many people believe that vaccines which contain the mercury-based preservative thimerosal are to blame for the autistic symptoms of their children. But the Institute of Medicine concluded that there is no link between vaccines and autism after examining the results of 19 major studies.

Federal health officials confirmed their belief in the safety of childhood vaccines, as a response to questions raised by the parents of a 9-year-old girl, who allegedly developed autistic symptoms after receiving childhood vaccine. Her parents said that shortly after the shots their daughter had fever, lost her appetite and stopped responding to verbal stimuli. The medical report showed she already suffered of an extremely rare mitochondrial disease. Although studies have not shown a link between vaccines and autism, many parents are still worried about a potential connection.

Autism is a disability which typically appears during the first years of life and it affects the child’s ability to communicate and interact with others. There is no known single cause for autism, but increased awareness and funding prove to be a great help for families with autistic children.

McCarthy’s son was diagnosed with autism and she wrote a book, which became a best-seller to talk about this experience. “Louder Than Words: A Mother’s Journey in Healing Autism” tells the story of two people who try to communicate using a language of love which is behind the words. She also speaks about her efforts to help Evan overcome his symptoms through medication, daily therapy and a special diet.

Jenny McCarty is also a vocal advocate for more autism-related research. They both said their son taught them how to love. McCarthy told People magazine last October that she calls Carrey the “autism whisperer.” “He's actually helped Evan get past some obstacles I couldn't," she said. “He speaks a language Evan understands.”