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Frequently Asked Questions About the Importance of Vaccines

Why are vaccines important?

In the U.S., vaccines have reduced or eliminated many infectious diseases that once routinely killed or harmed infants, children, and adults. Immunizing individuals also helps to protect the health of our community. Immunization prevents disease outbreaks by minimizing the spread of infection.

The United States enjoys one of the highest childhood immunization rates in the world along with record low rates of vaccine-preventable diseases.

However, the viruses and bacteria that cause vaccine-preventable disease and death still exist and can be passed on to people who are not protected by vaccines. Vaccine-preventable diseases have many social and economic costs: sick children miss school and can cause parents to lose time from work. These diseases also result in doctor's visits, hospitalizations, disabilities, and even premature deaths.

What has been the impact of vaccines?

Vaccines are considered to be one of the greatest public health achievements of the 20th Century. Vaccine-preventable disease levels in the U.S. are at or near record lows. However, we cannot take high immunization coverage levels for granted.

Before polio vaccine was available, 13,000 to 20,000 cases of paralytic polio were reported each year in the United States. These annual epidemics of polio often left thousands of victims--mostly children--in braces, crutches, wheelchairs, and iron lungs. The effects were life-long. Development of polio vaccines and implementation of polio immunization programs have nearly eradicated paralytic polio caused by wild polio viruses globally.

Before measles immunization was available, nearly everyone in the U.S. got measles. An average of 450 measles-associated deaths were reported each year between 1953 and 1963. Measles is no longer endemic in the United States

In 1964-1965, before rubella immunization was used routinely in the U.S., there was an epidemic of rubella that resulted in an estimated 20,000 infants born with CRS, with 2,100 neonatal deaths and 11,250 miscarriages. Of the 20,000 infants born with congenital rubella syndrome (CRS), 11,600 were deaf, 3,580 were blind, and 1,800 were mentally retarded. Rubella is no longer endemic in the United States.

Why do we need to keep immunizing our children if vaccine-preventable disease levels are now at record lows?

Even if only a few cases of a vaccine-preventable disease occur each year, if we take away the protection given by vaccination, more and more people will be infected and will spread disease to others. For some diseases, such as measles, 90% of the population needs to be vaccinated in order to prevent a disease from spreading if introduced into the population. Since we live in a global society, a case of measles can be brought in from other regions of the world where measles continues to thrive. If we do not continue to vaccinate against these diseases we would soon undo the progress we have made over the years. Diseases that are almost unknown would stage a comeback. Before long we would see epidemics of diseases that are nearly under control today. More children would get sick and more would die.

We vaccinate to protect our children, but also to protect our future. If we keep vaccinating now, parents in the future may be able to trust that diseases like polio and meningitis won't infect, cripple, or kill children. Vaccinations are one of the best ways to put an end to the serious effects of certain diseases.

Frequently Asked Questions About Thimerosal

What is thimerosal?

Thimerosa l is a mercury-containing preservative used in some vaccines and other products since the 1930s.

In July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure. Although the weight of the evidence to date suggests there is no causal association between thimerosal-containing vaccines and serious adverse health effects, HHS supports the reduction or elimination of thimerosal from vaccines as a precautionary measure and as a feasible step to decreasing the overall exposure of infants to mercury.

What vaccines still contain thimerosal?

Today, with the exception of some influenza vaccines, none of the vaccines used in the U.S. to routinely protect preschool children against 12 infectious diseases contain thimerosal as a preservative.

Does thimerosal cause autism?

There is no conclusive evidence that any vaccine or vaccine additive increases the risk of developing autism or any other behavior disorder. Rather, evidence is accumulating of lack of any harm resulting from exposure to vaccine containing-thimerosal as a preservative. In a 2004 report, the Institute of Medicine (IOM) concluded that there is no association between autism and vaccines that contain thimerosal as a preservative. Nonetheless, we are committed to investigating this issue to the fullest extent possible, using the best scientific methods available.

What would happen if thimerosal was eliminated from vaccines?

Thimerosal has been eliminated as a preservative from all vaccines routinely recommended for children 6 years of age and less used in the U.S., with the exception of influenza. The elimination of vaccines containing trace amounts of thimerosal would have a significant impact on the supply and availability of childhood vaccines, and as such, could seriously reduce our ability to protect children from vaccine-preventable diseases.

Is influenza vaccine that does not contain thimerosal as a preservative available this flu season (2005-2006)?

For the 2005-2006 flu season, a limited amount of influenza vaccine that does not contain thimerosal as a preservative is expected to be available. A preservative-free influenza vaccine made by Aventis Pasteur is approved for use in children 6-35 months of age. Also, the nasal-spray influenza vaccine (sold commercially as FluMist?) does not contain any thimerosal and can be given to healthy people 5 to 49 years of age who are not pregnant.

Is it safe for children to receive an influenza vaccine that contains thimerosal?

Yes. There is no convincing evidence of harm caused by the small doses of thimerosal preservative in influenza vaccines, except for minor effects like swelling and redness at the injection site.

Recent research suggests that healthy children under the age of 2 are more likely than older children and as likely as people over the age of 65 to be hospitalized with flu complications. Therefore, vaccination with reduced or standard thimerosal-content flu vaccine is encouraged when feasible in children, including those that are 6-23 months of age.

Is it safe for pregnant women to receive an influenza vaccine that contains thimerosal?

Yes. A study of influenza vaccination examining over 2,000 pregnant women demonstrated no adverse fetal effects associated with influenza vaccine. Case reports and limited studies indicate that pregnancy can increase the risk for serious medical complications of influenza. One study found that out of every 10,000 women in their third trimester of pregnancy during an average flu season, 25 will be hospitalized for flu related complications.

Additionally, influenza-associated excess deaths among pregnant women have been documented during influenza pandemics. Because pregnant women are at increased risk for influenza-related complications and because a substantial safety margin has been incorporated into the health guidance values for organic mercury exposure, the benefits of influenza vaccine with reduced or standard thimerosal content outweighs the theoretical risk, if any, of thimerosal.

Do you support legislative efforts to ban thimerosal?

There is currently no scientific justification for banning thimerosal and to do so could have major disruptions for national, state, and local vaccine supplies and the public health. If laws or policies preclude the use of vaccines containing trace amounts of thimerosal, the ability of doctors and health care providers to protect infants and children against the real and potentially serious health consequences posed by pertussis, influenza, tetanus, hepatitis, and diphtheria would be greatly, and unnecessarily, reduced.

The Department continues to work with vaccine manufacturers to facilitate the reduction or elimination of thimerosal from vaccines, and significant progress has been made. Today, with the exception of some influenza vaccines, none of the vaccines used in the U.S. to routinely protect preschool children against 12 infectious diseases contain thimerosal as a preservative.

Has the Government ?conspired? to keep from the public evidence of thimerosal's harm?

No, to the contrary. Since 1999, many people and organizations have undertaken independent studies and have worked to provide information on the potential risks of thimerosal. This research is available to the public. Moreover, the Institute of Medicine was asked to conduct a comprehensive, independent analysis of all the available information. The Committee reviewed epidemiologic evidence available for and against a causal relationship, as well as any case reports and clinical evidence. The Committee also heard presentations about key published research studies, as well as presentations about ongoing, unpublished research.

Following each review, the Committee provided a report that addressed their conclusions regarding: the causal relationship between the vaccine and adverse health effect; the biologic mechanisms that could account for the adverse health effect; and the significance of the vaccine safety concern in the context of society at large (e.g., the seriousness, treatment, complications of the wild-type disease and hypothesized adverse effects of the vaccine). Based on their conclusions, the Committee made recommendations for future activities (i.e. surveillance, research, policy, communication) regarding the vaccine safety concern. Two of the eight reviews conducted by the Committee were on thimerosal safety concerns: Thimerosal - Containing Vaccines and Neurodevelopmental Disorders (October 2001) and Vaccines and Autism (May 2004). IOM reports can be found at

After a careful review of the recommendations from the May 2004 report, Vaccines and Autism, CDC determined that at that time, there was no evidence based on hypotheses regarding vaccines and autism to make changes to the current childhood immunization schedule and recommendations.

Frequently Asked Questions About Autism and Autism Spectrum Disorders

What is Autism?

Autism (sometimes called ?classical autism?) is the most common condition in a group of developmental disorders known as the autism spectrum disorders (ASDs).

Autism is characterized by three distinctive behaviors. Autistic children have difficulties with social interaction, display problems with verbal and nonverbal communication, and exhibit repetitive behaviors or narrow, obsessive interests. These behaviors can range in impact from mild to disabling. Autism varies widely in its severity and symptoms and may go unrecognized, especially in mildly affected children or when more debilitating handicaps mask it. Scientists aren?t certain what causes autism, but it?s likely that both genetics and environment play a role.

Is there any treatment?

There is no cure for autism at the current time. Therapies and behavioral interventions are designed to remedy specific symptoms and can bring about substantial improvement. The ideal treatment plan coordinates therapies and interventions that target the core symptoms of autism: impaired social interaction, problems with verbal and nonverbal communication, and obsessive or repetitive routines and interests. Most professionals agree that the earlier the intervention, the better.

What is the prognosis?

For many children, autism symptoms improve with treatment and with age. Some children with autism grow up to lead normal or near-normal lives. Children whose language skills regress early in life, usually before the age of 3, appear to be at risk of developing epilepsy or seizure-like brain activity. During adolescence, some children with autism may become depressed or experience behavioral problems. Parents of these children should be ready to adjust treatment for their child as needed.

Is there an autism epidemic?

The question of whether there is an autism epidemic requires an understanding of trends in autism. Understanding autism trends is particularly difficult due to the lack of historical population-based tracking of autism rates and the fact that many early studies used different methods and a narrower definition of autism.

Although there have been some recent studies on autism prevalence trends, taken as a whole, their findings are inconclusive as to whether the apparent increase in prevalence is a result of increased diagnosis and awareness, and, if so, to what extent. Additional population-based monitoring is needed to assess prevalence trends, but, regardless of the past prevalence of autism, it is clear that more children are now being diagnosed today than were 10?30 years ago, making autism an urgent public health concern.

What is the incidence or prevalence of autism in the United States?

There is no full population count of all individuals with autism or ASD in the United States. CDC published the first population-based estimate of autism prevalence in a major U.S. metropolitan area in 2003. These data showed that 3.4 per 1,000 children in metropolitan Atlanta had an ASD. Summarizing this and several other major studies on autism prevalence, CDC estimates that between 2 and 6 per 1,000 children have an ASD.

Although much is unknown about the prevalence of autism, existing studies suggest that autism spectrum disorders (ASDs) are as much as four times more common among boys than girls, and unlike many other developmental disabilities, prevalence appears to be similar among black and white children.

Have the incidence and prevalence of autism increased significantly during the most recent decade?

We don?t know if autism/ASD incidence and prevalence have increased significantly. There is not a full population count of all individuals with autism or ASD in the United States, and there has never been such a population study. Determining trends in autism prevalence is also challenging due to the relative scarcity of past studies on ASD prevalence and the fact that many early studies used different methods and a narrower definition of autism. Although there have been some recent studies on autism prevalence trends, taken as a whole, their findings are inconclusive as to whether the apparent increase in prevalence is a result of increased diagnosis and awareness, and, if so, to what extent. Additional population-based monitoring is needed to assess prevalence trends, but, regardless of the past prevalence of autism, it is clear that more children are now being diagnosed than were 10?30 years ago.

What research is the Federal government doing on autism?


The Children's Health Act of 2000 required that a committee be formed to coordinate autism-related activities in the Department of Health and Human Services (HHS) and the Department of Education. The Interagency Autism Coordinating Committee (IACC) began in 2001. Its main role is to help agencies share information and to coordinate autism research and related activities in the agencies that are part of HHS.


NIH?s specific role in the broader research agenda is to find the genetic causes, genetic susceptibility, environmental causes, improve diagnosis, and to find potential treatments and preventions for autism. In addition to individual grants for research projects, NIH sponsors training, small grants, career support, and program projects that involve autism research. Scientists and families are working together in a variety of ways through new programs, and collaboration with advocacy groups and families helps the NIH set research priorities.

NIH recently developed a comprehensive plan known as the Autism Matrix. As one of its activities, the IACC convened a panel of outstanding scientists to assess the field of autism research and identify roadblocks that may be hindering progress in understanding the causes of autism and the best treatment options. As a result of this meeting, in November 2003, the IACC created the autism matrix that summarizes the state of science in autism as well as serves as a guide for future--both short and long term--research goals. The matrix is a living document, regularly reviewed by the IACC, as new discoveries emerge and research projects are launched.


The Centers for Disease Control and Prevention is conducting a range of research on autism incidence and prevalence. CDC now supports five regional Centers of Excellence for Autism and Developmental Disabilities Research and Epidemiology as well as supporting 18 states involved in monitoring autism and other developmental disabilities.

CDC has held listening sessions throughout the nation to hear directly from parents, health care providers, scientists, educators and other concerned citizens.

In addition, in early 2005, CDC launched the ?Learn the Signs. Act Early? campaign, designed to promote early identification and intervention for children with autism and other developmental disabilities.

How much is the Federal government spending on autism research?

In Fiscal Year 2006, NIH and CDC expect to spend $117 million to better understand the causes and potential treatments of autism through surveillance and basic and clinical research that will provide answers to the key questions of what causes this complex neurological disorder and how best to treat and prevent it. This amount represents an increase of $56 million (a 91% increase) in investments since Fiscal Year 2001.

Note: All HHS press releases, fact sheets and other press materials are available at

Last revised: July 21, 2005

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