Side Effects of Vaccinations


Vaccines are held accountable to very high levels of reliability and safety.  Because of this, they should have very few side effects while guaranteeing long-lasting and good immunity.  To ensure this type of quality is consistently met, vaccines are subjected to human and animal trials before they are officially registered. 

Regardless of this process, in the past some vaccinations have led to unwelcome results.

Why Vaccines are Not Risk-Free

The act of manufacturing vaccines involves some risk, because the processes involved use typically dangerous pathogens and pathogen constituents.  From the time that vaccines were first developed, some tragic incidents have taken place affecting individuals or groups of people.  These events can lead to exactly what the vaccination was intended to prevent:  severe illnesses causing permanent damage.

In many of these cases, poor quality vaccines or poorly produced vaccines were to blame, though the proper officials and manufacturers had claimed beforehand that the products were safe and effective.

Examples of Bad Vaccines

A particularly serious example of a vaccine gone wrong happened in 1976.  The American Center for Disease Control (CDC) had anticipated a dangerous outbreak of swine flu to be imminent.  A vaccine was produced and an effort was made to immunize as many Americans as possible.  Approximately 50 million people had been vaccinated before researchers realized the vaccines could lead to symptoms of paralysis.  More than a thousand people who were vaccinated suffered from paralysis (Guillain-Barre Syndrome).  The inoculation program was halted and the flu epidemic never happened.

Problems with Trials

The first and most fundamental problem with new vaccines is that they cannot be guaranteed to be effective or risk-free until they have been given to human beings on a large scale.  Before vaccines are registered, they are typically only tested on a relatively small research group of a few hundred to a few thousand participants, with an observation period that lasts just a few weeks.

Many questions also arise regarding the possibility of chemical, physical and immunological interactions in new vaccines that are combined with numerous active constituents.

Another problem with trials is that each person’s immune system can react differently to the ingredients contained in a vaccine. 

Scientists know, for instance, that live vaccines can trigger the illness they are supposed to protect against.  This only happens in a very small number of those vaccinated, however.  Such risks are thought to be acceptable when the risk is measured against the possibility of catching a disease through natural channels and then suffering from the full-blown side effects.

Additives That are Problematic

Sometimes the ingredients that are added to the vaccines (aside from the active constituents) are a problem.  These can be traces of substances left over from the manufacturing process.  Other additives that can react are those used in the preserving and stabilizing processes, including inactivating and detoxifying agents that are inserted to enhance the effectiveness of the vaccines.  Some of these substances can trigger allergies and can sometimes have toxic effects on certain individuals. 


Thiomersal (or in the U.S., called thimerosal) is thought to be particularly problematic.  This substance is a mercury-based preservative and has been banned in externally-used disinfectants, but it is still authorized for use in a few “dead” vaccines, including the vaccine for swine flu.  If mercury accumulates in the body it can lead to poisoning of the organs and brain damage.  Allergies are also a side effect of thiomersal use.    Guidelines say that the levels of mercury used in vaccines are within the permitted levels and, therefore, are not dangerous to humans. 

Women who are pregnant can request to receive a thiomersal-free flu vaccine, although the benefits of the vaccine are usually considered to outweigh the risk if one is not available.  At this time, there is no great evidence to suggest preservatives such as thiomersal add risk to the pregnancy.

In the UK, DTP and Hib vaccines contained thiomersal until 2004.  It was possible for infants to receive mercury through multiple vaccinations.  Although the levels of mercury did not exceed the recommendations of the World Health Organization, there was still a theoretical risk involved.  In 2004 the vaccines were updated to meet the international aim of reducing childhood exposure to mercury whenever and where ever possible.

Other Risky Compounds

A few other compounds are thought to be risky in vaccines.  Many contain aluminum compounds, which are typically used to strengthen the immune reaction.  Researchers believe both allergic and toxic reactions may result from the use of aluminum, although official guidelines are met and the quantities involved are very small.  It is known, however, that aluminum can trigger foreign body reactions such as tumor growth in the lymphatic system.  Accumulations of aluminum have also been found in the brains of people who suffer from Alzheimer’s disease, though there is no current evidence to suggest aluminum is causing the disease.

Formaldehyde is contained in many vaccines and is thought to be sub-toxic.  In higher concentrations, formaldehyde is known to cause a variety of health hazards, including allergies and cancer.

Foreign proteins can also be a problem, such as chicken protein.  Other problematic additives can include adjuvants or salts and antibiotics such as neomycin.

The Wrong Timing for Vaccinations

Some side effects occur from bad timing with the vaccinations.  For example:

  • Pregnant women should not be vaccinated with live vaccines.

  • Live vaccines are usually not advisable for those with weakened immune systems.

  • People who have recently had a serious operation should not receive vaccinations.

  • Those individuals with chronic inflammatory illnesses (such as diseases of the intestines or the lungs, as in chronic bronchitis) should not be given vaccinations.

  • People who are under a great deal of stress should not receive vaccines.

  • Anyone who is currently suffering from an illness (such as a cold accompanied by a fever) should wait until they recover to be vaccinated.


  1. Ada, G.L. (2000).Vaccination : the facts, the fears, the future. Sydney, N.S.W. : Allen & Unwin
  2. Godfrey, M. & Anderson, R. (2002). Exploding the myth of vaccination. Tauranga : R. Anderson
  3. Scheibner, V. (1993). Vaccination : 100 years of orthodox research shows that vaccines represent a medical assault on the immune system. Blackheath, NSW : V. Scheibner
  4. Studer, Hans-Peter. (2010). Vaccination : a guide for making personal choices. Edinburgh : Floris

Posted in Side Effects of Vaccinations

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