Is there a link between vaccines and autism?

The short answer to this question is: there is none. But why is this idea so prevalent, and how did it come about?


The truth about vaccines

The name you need to know is Andrew Wakefield. In February 1998, the discredited medical researcher and disgraced former doctor published a paper in the journal Lancet, highlighting autistic symptoms exhibited by eight children admitted to the Royal Free Hospital in Hampstead after receiving the measles, mumps and rubella (MMR) vaccine.

According to Wakefield, not only did the children exhibit symptoms associated with autism, they suffered stomach and intestine problems. This led him to suggest that the MMR vaccine caused a reaction and changes to these areas, that then affected normal brain development in the children.

However, Wakefield’s sample size was very small, and had no control subjects. This made it difficult to determine if the vaccine directly caused the symptoms and if the timing is only coincidental. An ‘association’ was inferred, misconstrued and conflated to causation.

The findings of this study have not been replicated since, but damage had been done.

This report was the beginning of decades-long struggle by public health officials to debunk inaccurate reports about the safety of vaccines for children, particularly the combined MMR vaccine. It took Lancet more than 10 years to retract the paper from scientific literature, and only in the wake of award-winning investigative reports by British reporter Brian Deer.

Deer’s investigations uncovered holes and inconsistencies with good research practice in Wakefield’s study cohort, including the fact that the children were pre-selected for the study.

Some parents were paid for the children’s visits to the hospital and Wakefield received payments prior to the start of the study, to prove that the MMR vaccine caused previously-unseen syndromes. These findings were to be used in a legal case on behalf of the affected families. Wakefield had also filed a patent for a vaccine that he touted as safer than the current MMR vaccine.

This clear conflict of interest and unethical practices led to the longest professional misconduct hearing in the UK by the General Medical Council, which resulted in Wakefield’s erasure from the council and the end of his medical career in 2010.


Breaking down the myths

Several arguments are often raised in defense of not vaccinating with the combined MMR vaccine. The three main arguments raised are:

  1. The combination vaccine causes damage to intestinal lining, and allows entrance of proteins and delivery to the brain, affecting development.
  2. The preservative thimerosal used in vaccines is toxic to the central nervous system.
  3. The administration of multiple vaccines simultaneously overwhelms and weakens the immune system.

Sounds like good enough reasons to be doubtful? Not quite.

Myth 1: Damage to the intestinal lining affects development

This argument was first highlighted in Wakefield’s Lancet paper. His theory was that the damage to the intestines brought about the changes in children’s brain development.

But many studies have pointed out that these symptoms do not always appear before Autism Spectrum Disorder (ASD) could be detected in all children. Additionally, the proteins always referred to as the culprit responsible for ASD have never been identified.

Large studies were conducted in the US and Europe in the years following Wakefield’s paper. These studies used and included different designs, large sample sizes, reliable historical data through vaccination records and similar vaccines and vaccination schedules.

Not even one study showed any relationship between the use of the vaccine and the development of autism.

In one study in the UK, even when updated in 2001 to include longer exposure and a second dose of the vaccine, the findings remained unchanged, with no differences observed in rate of diagnoses after introduction of the vaccine.

In 2015, a large study including nearly 95,000 children was conducted and funded by the National Institute of Health, the National Institute of Mental Health, and the US Department of Health & Human Services.

The study found no link and no increased risk from use of MMR vaccine, even when older siblings were in the autism spectrum.

Myth 2: Toxic thimerosal in vaccines

Thimerosal, an organic compound of ethyl-mercury, has been used in preparations of vaccines, as an antibacterial or antifungal agent, for more than 50 years.

Similar to the previous studies looking into a relationship between MMR and autism, specific studies looking into relationship between thimerosal and autism were conducted. Even when thimerosal was removed, the rates of diagnoses remain unchanged. All seven studies conducted did not find any relationship between this agent and autism.

So why did people think that thimerosal could be responsible?

This link between mercury poisoning and autism began as a hypothesis proposed by a group of US scientists in the early 2000s. Their paper theorised that the link is possible because of similarities observed in symptoms for mercury poisoning and ASD.

Like in Wakefield’s paper, the team associated the appearance of symptoms after vaccination in some children. They also suggested the rise in diagnoses paralleled the rise in the use of vaccines in the population.

While those were valid concerns, the symptoms of mercury poisoning and ASD were found to be quite different. Concurrent environmental changes such as the child’s age, growth and development were not considered.

However, people were still doubtful because mercury is known to be toxic. The large body of literature on the subject often refers to the neurotoxicity of the methylform of mercury. This is quite different from the ethyl-form, which is present in thimerosal. It is easy to overestimate the damage that can be caused by ethyl-form.

Despite the large body of data showing no link between autism and mercury, the US Food and Drug Administration (FDA) introduced the FDA Modernization Act, which mandated that any use of mercury in food and drugs must be identified and quantified.

As a precautionary measure in 1999, the American Academy of Pediatrics and the US Public Health Service recommended that mercury must be removed from vaccines given to young children. Unfortunately, anti-vaccine advocates immediately seized this decision as proof of the link between mercury and autism.

Myth 3: Vaccines overwhelm the immune system

Another argument raised in defense of vaccine hesitancy is the recommended schedule that calls for many vaccines in the first two years of children’s lives. These multiple vaccine doses are believed to overwhelm and weaken the immune system.

This theory was particularly popular after nine-year-old American Hannah Poling received compensation from the Vaccine Injury Compensation Program in 2008. Hannah had a rare condition – mitochondrial enzyme deficiency – and her health deteriorated after the administration of five vaccines when she was 19 months old.

While there is a case to be made that vaccine injury is real, this theory is inaccurate as vaccines are not known to overwhelm the immune system. In fact, some scientists theorise that the immune system would be able to withstand and respond to thousands of vaccines at the same time.

If vaccines do weaken the immune system, vaccinated individuals would be more likely to suffer from infections, compared to unvaccinated individuals. This is not the case.

Studies have shown that after an unvaccinated person comes down with a vaccine-preventable disease, they are more likely to suffer from severe infections in the future. One such example is the predisposition to pneumococcal pneumonia, after initial infection with vaccine-preventable influenza.

In a nutshell, many studies have been devoted into exploring a possible link between the MMR vaccine and autism. To date, there is yet a compelling study that has shown a significant association between the two.


By Najmin Tajudin

A biologist by training, Najmin Tajudin has worked as a management consultant, took the Early Childhood Course in Montessori Theory and Methodology, and ran a community-supported agriculture (CSA) program out of an integrated goat farm. With all 3 kids finally in school, Najmin is looking forward to spending more time on reading books and writing. 


For Part 1 and 2 of this series, go to What are vaccines and why do we need them? and Herd immunity: We’re all in this together.

Vaccinations are found to work best when most – or ideally, all – of the population have been inoculated against the same infectious disease. This is known as ‘herd immunity’.

This article is the second in a series which will attempt to give a basic overview of vaccines and how they work.


Have you herd? Immunity is in

When a large number of individuals in a community or country are vaccinated, the number of individuals that are likely to be immune to infections is high. This means the risk of an epidemic outbreak is low where most of the population is unlikely to be sick with a particular illness.

In terms of vaccination, herd immunity would be the critical number or threshold level required to reduce cases of infection. This required threshold could differ from one infectious disease to another.

For example, in order to achieve herd immunity for measles, the vaccine coverage in the community must be higher than 90-95%. This means if more than 95% of the population are vaccinated against measles, it is unlikely that a measles outbreak would occur because it would not be able to spread as widely and quickly.

One of the most important things to understand about herd immunity is that in communities with a high vaccination coverage, indirect protection for individuals that cannot be vaccinated can be achieved.

This includes very young children, the elderly and individuals with lower-than-normal immunity, like people receiving treatment for cancer or who have long-term conditions such as kidney disease.


Understanding the concept

With more data and research, scientists have realised that vaccines do not provide perfect immunity. Other factors include different levels of interaction between certain groups.

For example, school-going children are considered to be a high-risk group for the transmission of influenza, or the flu.

In Japan, in the 90s, researchers carrying out a selective influenza vaccination program which targeted school children observed reduced rates of sickness and death among the elderly in the population, a group vulnerable to infection.

This perfectly illustrates the concept of herd immunity in action: when a high-risk group is given sufficient coverage, the disease spreads more slowly or less easily in the rest of the population.

Vaccinations carry certain costs, such as money, time and possible side effects. Because of this, some individuals or groups choose to freeload or not to inoculate because they rely on the indirect protection from the rest of the population.

This has raised heated debates about individual choices versus the needs of a community. While vaccination remains a personal choice, people have been reminded that individual choices have a significant and real impact on community health.


Low herd immunity leads to epidemics

When people or groups choose not to vaccinate due to personal safety concerns or religious beliefs, more outbreaks of vaccine-preventable diseases happen.

In recent years, in the US, measles outbreaks have been  linked to particular communities. Just a few months ago, another measles outbreak was reported in the Somali-American community in Minnesota.

This incidence showed how playing on parents’ fears, misunderstandings and lack of knowledge about vaccine safety can have detrimental effects on public health.

It began with an inaccurate report linking rising rates of autism in Somali-American children to the use of the measles, mumps and rubella (MMR) vaccine.  This view was encouraged in targeted community outreach programs, by anti-vaccine groups.

This led to a rapid decline in vaccine coverage among children under two years of age in the community, from 92% in 2008, to 42% in recent years. The herd immunity below the level required for protection from the disease consequently and predictably, resulted in a measles outbreak in the state.

Since then, state officials have made attempts to combat the outbreak medically, which is expensive and time-consuming, and to reverse the decade-long beliefs that the vaccine is no longer safe for children.


No jab? No pay and no play

Governments around the world are taking a tougher stance against parents and families who choose not to vaccinate their children.

In Australia, children are required to have their immunisation status updated on the Australian Childhood Immunisation Register. The information here is linked to social security or welfare payments as well as a family’s entitlement to access childcare.

Essentially, if your child has not been fully vaccinated, families receive lower fortnightly payments and their child can be refused access to childcare services. Vaccination objection is not seen as a valid exemption and if an outbreak of a disease occurs, unimmunised children can be excluded from child care for a time.

In Germany this year, the health minister spoke about introducing a law to fine parents up to €2500 for failing to seek advice on vaccination. Kindergartens are expected to report on parents who fail to prove that they have had medical consultations, and can expel children who are not vaccinated. These tougher laws were in response to a measles outbreak earlier in the year, with 410 cases recorded by mid-April.

Italy has also adopted stricter measures. Recently, it was announced that all children had to be vaccinated against 12 common childhood illnesses before enrolment into state-run schools, due to coverage falling below 95% as recommended by WHO. Parents could also be fined if vaccination is not completed by the time their children turn six years old.

Compliance and coverage remain high in Europe, where vaccinations are monitored by the Vaccine European New Integrated Collaboration Effort (VENICE). However, the rise of hesitancy in parents must be addressed to ensure that communities remain protected from future vaccine-preventable outbreaks.


By Najmin Tajudin

A biologist by training, Najmin Tajudin has worked as a management consultant, took the Early Childhood Course in Montessori Theory and Methodology, and ran a community-supported agriculture (CSA) program out of an integrated goat farm. With all 3 kids finally in school, Najmin is looking forward to spending more time on reading books and writing. 



If you missed Part 1 of this series, go to What are vaccines and why do we need them?.

Vaccines have an interesting history and were born out of necessity to prevent and control diseases. Most of us view vaccination as the norm, but what’s its history and how did it become part of general health practice?

This article is the first in a series, which will attempt to give a basic overview of vaccines and how they work. It will also discuss the concept of herd immunity. Other articles in the series will address some of the concerns associated with vaccination.


Bovine intervention

Literature credits 18th century Englishman Edward Jenner as the one who began a series of experiments that would change how infectious diseases are fought and prevented.

During this period, it was common knowledge that milkmaids were less likely to contract smallpox – a devastating disease that killed hundreds of thousands of people in Europe alone, especially infants.

Jenner believed that through their work, the milkmaids would have been exposed to the milder cowpox, and this exposure could provide some form of immunity against smallpox.

He began conducting experiments, using pus from cowpox (yep, you read that right), from a milkmaid and injecting it into a young child. After contracting cowpox and recovering, the child was then injected with smallpox.

When he did not develop smallpox, Jenner expanded his research and tested 23 other individuals. He was so utterly convinced of his theories that he even tested his methods on his 11-month old son. He called this vaccinae, from the root word, vacca, which is Latin for “cow”.


Modern medicine

Over the next 150 years, Jenner’s work spurred further research into vaccination, as the primary method of control for several common infectious diseases.

According to the World Health Organisation (WHO), 116 million children or 86% of children worldwide, receive basic vaccines every year.

It is believed to have reduced cases of infectious diseases in major parts of the world.  Diseases like diphtheria, polio and smallpox are now almost eliminated from the United States.

More recently, Mexico has seen a striking reduction in mortality rate in children below five years of age, only three years after the introduction of the vaccine for rotavirus, the most common cause of vomiting and diarrhea.

The use of vaccines helps prevent common bacterial infections prevents an estimated 2-3 million deaths annually, and could also help in reducing the use of antibiotics. This is particularly important, as doctors have reported the rise of antibiotic resistance in recent years.

Viral vaccines would also reduce viral infections, which are often mistaken for bacterial infections, and ineffectively treated with antibiotics.


What’s in a vaccine?

Generally speaking, vaccines work on the same principles in Jenner’s work with smallpox.

An ‘agent’ is introduced into a healthy individual, which triggers an immune response in the vaccinated individual.  This response would then provide protection in the event of a ‘true’ infection in the future.

Each vaccine is designed based on several factors, such as the microorganism or parasite responsible for the infection, the mechanisms involved in the infection, and other practical considerations, such as the geographical area where the vaccine would be used.

While the principle behind vaccines remains the same, the agent responsible for triggering the desired immune response would be different from one disease to another.

It could contain a whole, but weakened form of the infectious agents, also referred to as live and attenuated forms.  Examples include the MMR for measles, mumps and rubella, and Bacillus-Calmette- Guérin (BCG), which could provide immunity against tuberculosis (TB).

In other vaccines, the whole agents are inactivated to reduce the risk of infection. The hepatitis A and influenza vaccines are examples of this.

In yet other cases, different parts of the organisms causing infections can be used. For example, the DTaP or Tdap vaccine uses specific parts of the agents responsible for diphtheria and tetanus infections, in addition to the inactive organism that causes pertussis, or whooping cough. These combined agents provide immunity against all three diseases.

Meanwhile, conjugate vaccines such as the pneumococcal conjugate and Haemophilus influenzae type B (Hib) vaccines use specific proteins to stimulate a greater immune response.


When to vaccinate?

In the US, the Centre for Disease Control and Prevention or the CDC, has drawn up a recommended timeline for vaccination. This schedule, however, might differ from one country to another.

In Malaysia, the National Immunisation Program (NIP) was developed based on the Expanded Immunisation Program or EIP, recommended by the World Health Organisation (WHO), and covers 10 common childhood diseases.

Table 1. Overview of Vaccines for Some Common Childhood Illnesses and Recommended Schedule for the US and Malaysia

Vaccine Primary/ Major Components CDC-Recommended Schedule (US)

(Dose and age)

National Immunisation Program (Malaysia)

(Dose and age)


(measles, mumps and rubella)

Mixture of live ‘attenuated’ viruses of the 3 diseases. 1st  – 12-15 months

2nd – 4-6 years

1st – 9 months

2nd – 12 months

Booster – 7 years

DTaP/ Tdap

(diphtheria, tetanus, pertussis)

Parts of diphtheria and tetanus-causing organisms, and killed whole organism responsible for pertussis. 1st  – 2 months

2nd – 4 months

3rd – 6 months

4th – 15-18 months

5th – 4-6 years

1st – 2 months

2nd – 3 months

3rd– 5 months

4th – 18 months

DT Booster- 7 years

BCG: Bacillus- Calmette- Guérin


Live bacteria. Not recommended in the US

Only for individuals that meet specific criteria.

At birth
Hep B

(hepatitis B)

Specific parts or antigens. 1st – At birth

2-3 shots over a period of the first 6 months.

1st – At birth

2nd– 1 month

3rd– 6 months


(infection caused by Haemophilus influenza type b e.g. meningitis, pneumonia and epiglotittis)

Conjugate vaccine. 1st – 2 months

2nd – 4 months

3rd – 6 months

Booster- 12-15 months

1st – 2 months

2nd – 3 months

3rd – 5 months

Booster- 18 months

Polio Two types:

i.                  Inactivated virus introduced via injection (IPV).

ii.                  Live, attenuated virus introduced orally.

1st – 2 months

2nd – 4 months

3rd – 6-18 months

Booster- 4-6 years


(IPV only since 2000)

1st – 2 months

2nd – 3 months

3rd – 5 months

Booster- 18 months



These vaccines are provided free of charge at all Ministry of Health (MOH) facilities, including all health clinics, mother and child clinics, K1 Malaysia and village clinics.

The BCG vaccine against TB is introduced at birth, as TB is still regularly found in Malaysia. Additional vaccines against Japanese Encephalitis are given at nine months and 21 months to residents of Sarawak, where it is still found.

Malaysia has also implemented a comprehensive School Health Program, established by the Ministry of Health and the Ministry of Education in 1967. Under the program, students in all primary and secondary government schools are given vaccinations in schools, as part of its objective to provide universal access to basic health services.


By Najmin Tajudin

A biologist by training, Najmin Tajudin has worked as a management consultant, took the Early Childhood Course in Montessori Theory and Methodology, and ran a community-supported agriculture (CSA) program out of an integrated goat farm. With all 3 kids finally in school, Najmin is looking forward to spending more time on reading books and writing. 


For Part 2 of this series, go to Herd immunity: We’re all in this together.