Vaccines

Any medicine (including vaccines and herbal/homeopathic medicines) can cause an unwanted side effect, commonly referred to as an adverse drug reaction (ADR) by healthcare professionals.

What is a vaccine?

A vaccine is a medicine which is administered to prevent a specific disease.

Examples include:

Childhood vaccinations such as MMR (measles, mumps, and rubella) and HPV (human papillomavirus)
Vaccinations available in adulthood such as tetanus, shingles and seasonal influenza (flu)
Travel vaccines such as polio, typhoid and hepatitis A

What vaccines are used for

Vaccines are simple and effective ways to protect you against harmful diseases. They work by training your body’s natural defence, the immune system, to recognise specific infections and produce antibodies to prevent diseases. Vaccines are mainly given through an injection but can also be given orally (by mouth) or sprayed into nose.

Side effects and adverse reactions to vaccines

A side effect is an unexpected effect that happens in addition to the main intended effect (of the vaccine). An adverse reaction is when the resulting effect causes harm (this can be both physical and mental).

Side effects can happen at any time, but particularly when you are given a vaccine for the first time. Most side effects are normal, mild and last only a couple of days. This occurs as the vaccine teaches your immune system how to protect your body from the disease.

Side effects could also be the result of defective, fake vaccines (one that is not authentic).

Defective vaccines

A defective vaccine is a product that is not working properly or not to the manufacturer’s specifications.

Fake/unauthorised vaccines

A fake vaccine is a product that tries to pass off as a genuine authorised vaccine. An unauthorised vaccine does not hold the relevant authorisations for sale and supply to patients in the UK and the MHRA has no evidence of its safety, quality or effectiveness.

Why report side effects to the Yellow Card scheme?

Everyone has a different genetic makeup and therefore it is very difficult to predict whether an individual will experience a side effect. Whether you are a healthcare professional or a member of the public, you can help others by reporting side effects which you or your patients experience to the MHRA Yellow Card scheme. Reports help us gain a better understanding of vaccine interactions and safeguard patients through vigilant monitoring.

Find out more about the Yellow Card scheme, including how to report.