Immunization Side Effects

Immunization side effects are usually mild and only occur in a few patients. However, vaccines, like all medicines, are capable of causing serious side effects, but these serious adverse events are extremely rare.

The risk of these adverse effects is much lower then the benefit that the vaccines (immunizations) confer. This page's aim is to provide you with the information you need to make a fully informed decision and it is not meant to put you off protecting your child with immunizations.

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Common Immunisation Side Effects

The most common immunisation side effects are generally mild and self-limiting, which means they are not serious and they go away by themselves. They include:

  • Local redness or swelling at the site of the injection.
  • Fever – most fevers are mild but in occasional cases, the fever can be accompanied by a seizure – febrile seizures such as this are benign although they are very scary at the time. To read more on febrile seizures, click here
  • Crying a bit more than usual
  • Poor appetite
  • Rash – often seen a week to 10 days after MMR
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Serious Immunization Side Effects

Serious immunisation side effects are not common and do not usually cause any lasting damage or illness. They include:

  • Allergic reactions – the most severe type of allergic reaction is an anaphylactic reaction and this usually occurs within 30 minutes of having the injection. This is why you are asked to wait after the injection. . Treatment is with Adrenaline (Epinephrine) by injection. It is rare for anaphylaxis to occur with immunization but if your child has had an anaphylactic reaction, he will not be able to have that particular immunization again. To read more on anaphylaxis, click here
  • Hypotonic Hyporesponsive Episodes (HHE) – these are when your baby becomes pale floppy and not very responsive. This usually happens within 12 hours of the immunization and can last up to 36 hours. It is very scary and usually parents will call an ambulance. Other than making sure the airway is not blocked and there is enough oxygen in the body, there is no specific treatment for HHE and it usually gets better by itself. There are no long term side effects and children can usually have future immunizations. The vaccine most likely to cause HHE is pertussis (whooping cough) vaccine - luckily it doesn’t occur with the acellular pertussis immunization (aP on the schedule), so it is less common these days as more countries are using acellular pertussis immunization
  • Serum sickness - a type of hypersensitivity reaction that causes a rash, fever and sore joints and can occur days after the vaccination. Treatment is anti-inflammatory agents such as Ibuprofen. There are no long term consequences of this type of immunization side effect.

Immunizations are Safer than the Diseases

Childhood immunizations are generally very safe. It is extremely rare for permanent damage to be the result of immunization side effects. Children are much less likely to get permanent side effects from immunizations than they are to get serious permanent side effects from the actual disease.

Immunizations do not cause autism. To read more, click here

To read about the how immunizations work, click here.


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References and Resources


To go to the top of the childhood immunization side effects page, click here

To go to the Infant Immunization Schedule page, click here

To read about  autism and immunizations page, click here

To read about how immunizations for kids work, click here

To go to the main Immunization page, click here

To go to the Infections page, click here

To return Home, click here


Last reviewed 21 May 2011

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Dr Maud MD

Dr Maud MD (MBChB, FRACP, FRCPCH), a specialist pediatrician, provides health information and medical advice for parents of babies and toddlers. Read more about Dr Maud.



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