March 6, 2008 -- What are the real benefits -- and the real risks -- of U.S. childhood vaccines? Do vaccines cause autism? Why do some vaccines still contain the controversial, mercury-based compound thimerosal? WebMD went to experts for the answers to some frequently asked questions:
1. What are vaccines?
"Vaccines help our bodies make protection against life-threatening infectious diseases," says Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases.
When a germ invades the body, the immune system recognizes it as a foreign invader. This sets off a cascade of events. The immune system makes antibodies, which are specialized molecules that stick to the invader and either inactivate it or mark it for destruction. Specialized immune cells also seek out and destroy germs and cells in which germs are multiplying. Other immune cells remember the germ so the next time a germ of the same kind tries to invade the body, the immune system will be able to mount an immediate response.
Vaccines offer a shortcut to immunity by raising protective immune responses before a germ invades. This gives the body a crucial head start that lets it prevent dangerous infections or make them less severe.
2. I heard that the U.S. government says childhood vaccinations might cause autism and something called mitochondrial disease. Is this true?
In March 2008, the Division of Vaccine Injury Compensation (DVIC) at the Department of Health and Human Services agreed there is a possibility that vaccination "aggravated an underlying mitochondrial disorder" in a young girl. The girl suffered "a regressive encephalopathy with features of autism spectrum disorder" after receiving five standard childhood vaccines in July 2000. The DVIC agreed that the girl and her family should be compensated.
Mitochondria are the energy-making structures inside the cells of our bodies. They have their own DNA, which we inherit directly from our mothers. Mitochondrial diseases or disorders are caused by defects in mitochondrial DNA, or by defects in regular DNA that affect mitochondrial function.
People with mitochondrial disease may get too little energy to power the immune system, the nervous system, and/or other important bodily functions. Or their dysfunctional mitochondria allow toxins to build up within cells.
The case settled by the DVIC is a legal case, not a scientific study. The DVIC agreed only that it is biologically plausible for a girl with a mitochondrial disorder to have been injured by her vaccination. The DVIC did not say that vaccines cause autism.
Does vaccination truly aggravate mitochondrial disease? WebMD asked Chuck Mohan, executive director and CEO of the United Mitochondrial Disease Foundation.
"There is no scientific proof that vaccines cause mitochondrial disease or autism, but there is very little scientific research in this area," Mohan says. "Persons with mitochondrial disease don't necessarily have autism, and persons with autism don't necessarily have mitochondrial disease. The tie-in is that in this case, mitochondrial disease was exacerbated by vaccination."
Louis Elsas, MD, professor of medical genetics at the University of Miami Miller School of Medicine, says vaccination might very well trigger serious symptoms in people with mitochondrial disorders.
"But this could happen if a person with mitochondrial DNA defects gets a cold or one of the diseases the vaccine is supposed to stop," Elsas tells WebMD.
People worried that their children might be particularly susceptible to vaccines or medications may wish to seek genetic testing, Elsas says.
(Are you changing your child's vaccine schedule because of autism fears? Tell us what you're thinking on the Autism Support Group message board.)
3. Some autism advocacy groups say vaccines -- especially those that contain the mercury-based compound thimerosal -- can cause autism and brain damage. They are sincerely worried. Why shouldn't I believe them?
"Autism is a serious and very challenging disease for families to cope with," says Schuchat. "Parents want explanations of how this happened to their child. lt is important for us to support research and programs that will help us better understand the factors that lead to autism and to find the best treatments. But a very large number of scientific studies have been carried out, and extensive scientific reviews, that have concluded there is no causal connection between vaccines or the preservative thimerosal and autism.
"There are hundreds of studies that have looked one way or another at these issues. Some are animal studies, some are toxicology studies, and some are human studies with a number of different designs. There have been efforts to review the evidence, the direct human evidence and the indirect animal evidence. Those reviews don't just look at the last sentence in the article but look at the study methods and ask if the methods and the results justify the conclusions. [The most recent] extensive review was carried out by the Institute of Medicine with a number of experts and concluded the information from all of these studies taken together did not support a causal association [between vaccines and autism].
"They concluded that other factors or explanations for autism should be sought. And more recently, people have thought that genetic and some environmental research may be more promising than continuing to pursue thimerosal."
4. If only to err on the side of caution, why can't all vaccines be thimerosal-free?
"The vaccines that are given to children in the U.S. are nearly thimerosal free," says Schuchat. "All but the flu vaccines that are given to young children do not contain thimerosal. Some formulations of flu vaccine are thimerosal-free and some are not. So the pediatric vaccine supply is nearly thimerosal-free. Thimerosal is a preservative that keeps germs from overgrowing. So vials of vaccine that are multiple doses, 20 or 30 doses, have a preservative to keep them from bacterial contamination. It was put in there because people died from vaccines that were contaminated.
"To get thimerosal out of all vaccines would require additional construction of facilities to be able to prepare vaccines differently. So there have been major changes since 1999 in removing thimerosal from the vaccine supply, but it is a many-year process. Although there is no compelling evidence that thimerosal caused harm, the concerns that have been raised have led to this lengthy process.
"Some of the pharmaceutical companies are going through the transition. Not looking for another preservative, but looking for production capacity to make that change.
"But right now, for every childhood vaccine, there is a thimerosal-free alternative."
5. Can vaccines cause the diseases they are supposed to prevent? Every year you hear people say, "I got my flu shot and then I came down with the flu."
"Flu vaccine does not cause the flu," says Schuchat. "Many vaccines do not provide 100% protection, but they decrease the chances of getting an infection. Even so, they don't reduce the chances to zero. Sometimes, even a person who is vaccinated can get an infection the vaccine was supposed to prevent. But the vaccines used today don't cause the diseases they are supposed to prevent."
6. What harms do vaccines do?
"There can be side effects from each individual vaccine," says Schuchat. "The most common side effect is pain or swelling at the site of injection. For each vaccine recommended, the CDC is required to provide a vaccine information statement to a parent or patient receiving one of the vaccines. It lists background information on benefits and risks. Most vaccines do not have serious adverse events associated with them.
"But some do. For instance, the flu vaccine is made from eggs. People with egg allergies should not receive the flu vaccine because they can have a serious reaction. So there are questions doctors use to screen people before getting any vaccine to make sure they don't have special risks. For the vast majority of childhood vaccines, there are very few of these.
"There is a possibility -- it is not yet clear -- but with the meningococcal conjugate vaccine, there have been reports of Guillain-Barre syndrome. We do not yet know if this is a true vaccine-related risk. But if it is there, it happens at the rate of about one per million doses administered. And that has been added to the vaccine information sheet."
7. What good do vaccines do?
"For every year's worth of vaccines we give out," says Schuchat, "over the life of the people receiving them, we prevent 33,000 deaths and 14 million illnesses with direct medical savings of $9.9 billion dollars and total societal savings of $43 billion. So vaccines greatly reduce life-threatening illnesses and deaths and also save money.
"Vaccines provide direct protection to the person immunized. But they also protect the family and the community.
"For example, infants and toddlers have since the year 2000 received pneumococcal vaccines to protect against dangerous brain, blood, lung, ear, and sinus infections. By vaccinating young children, we dramatically reduced disease in children but also dramatically reduced disease in adults by preventing spread of illness from children to others. That is the case for many vaccines: We get population protection. We protect the individual, and also others.
"For flu, we recommend vaccinating people at high risk of complications, but also recommend vaccination for their contacts, for parents of young children or caretakers of the elderly, because they prevent the person from spreading the disease to the vulnerable person."
8. How can I maximize my child's protection and minimize his or her risk?
"Many vaccines are recommended for every child," says Schuchat. "It is important to talk to your health care provider, to make regular appointments, and to keep them -- and to ask if any vaccinations are due and if your child is up to date. It is important to immunize but also important to immunize on time because gaps can leave a child vulnerable. You can keep a record of which immunizations they have gotten, something that is good for you and for their schools to have."
"In terms of reducing a child's risk of infectious diseases, hand washing is really important. A lot of these diseases can be spread when germs get on our hands.
"It is very appropriate for parents to want information and to keep themselves informed. The vaccine information statements are a good source of information. Parents want to protect children and want good information. They must be comfortable raising questions with their doctor or nurse and getting the answers they are looking for. After all, the first job of parents is to protect their child's health."
9. Wouldn't it be safer if I refuse to vaccinate my child?
"Vaccines protect against serious and life-threatening infections," says Schuchat. "So the choice to not immunize your child is like playing Russian roulette. The diseases are still out there. Other nations in the world don't have as strong an immunization system as we do, and those germs can come from anywhere. Leaving your child unimmunized is really putting your child and your family at risk."
10. Why are some vaccines given a few times in childhood, and others given every year?
"Before a vaccine is licensed, it is tested to understand how well it can protect," says Schuchat. "Some vaccines need multiple doses to provide protection, and some need boosters five or 10 years later to make sure the protection stays active. Some vaccines given in childhood wear off as a child becomes a teen, so a new vaccination is needed.