Celebrities Jim Carrey and Jenny McCarthy are hoping to use their star power to raise awareness about the dangers of childhood vaccinations that they believe are linked to diseases like autism.
The couple will be leading the "Green Our Vaccines" march and rally in Washington, D.C., on Wednesday.
The actors have joined with other national autism advocacy groups to press for the elimination of toxins from children's vaccines and to change children's vaccination schedules.
"In 1983 the shot schedule was 10. That's when autism was 1 in 10,000. Now there's 36, and autism is one in 150," McCarthy said today in an exclusive interview on "Good Morning America." "All arrows point to one direction."
There has been heated debate about the prevalance of autisim among children and a link to vaccinations.
Many parents of autistic children believe that vaccines, especially those containing the mercury-based preservative thimerosal, are to blame for bringing on their children's autistic symptoms.
But the mainstream medical community has repeatedly said there is no proven link between vaccines and autism.
The Institute of Medicine, part of the National Academy of Sciences, reviewed 19 major studies that tracked thousands of kids, and all showed no link between vaccines and autism.
Still, thimerosal was removed from essentially all childhood vaccines in 2001 in response to autism fears. But autism rates have continued to rise, leaving many experts to conclude that thimerosal could not be the cause.
McCarthy's 6-year-old son, Evan, was diagnosed with autism, and the actress has become a vocal advocate for more autism-related research. McCarthy's best-selling book, "Louder Than Words: A Mother's Journey in Healing Autism," chronicles her efforts to help her son overcome his symptoms through a special diet, medication and daily therapy.
Many doctors worry that linking autism to vaccines could deter parents from vaccinating their children, leading to an outbreak of childhood diseases like measles, mumps and rubella, which have been virtually delimited thanks to childhood immunization but are now threatening again.
The CDC is bracing for the worst measles outbreak since 2001, with nine states already reporting cases this year. In 2006, more than 6,500 Americans were sickened by mumps, the worst outbreak in 20 years.
McCarthy and Carrey said that while they do support immunization, they and their allies believe children receive "too many vaccines, too soon, many of which are toxic."
"We are not here to destroy the vaccine program. We're here to lend our voices for the millions of people calling for balance and moderation when it calls to substances that we give our children," Carey said. "They are not bottomless pits that you endlessly pour the substances into. You have to consider the cumulative effect. Not only that, the possible interaction. Every other drug has interaction with other drugs and yet they assume vaccines won't."
McCarthy, 35, was Playboy's 1994 Playmate of the Year and used her outrageous sense of humor to begin a career as a film and television personality.
McCarthy and Evan's father, John Asher, divorced in August 2005. A year later, McCarthy and comedian-actor Jim Carrey went public with their relationship.
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."
For parents concerned about their babies getting too many shots, the Infectious Disease Society of America recommends National Network for Immunization Information's Web site.
Find out more about the march at Talking About Curing Autism.