Case study: Vaccine error

...Dr M administers the vaccine but later realises he has given the patient the wrong one...

  • Date: 22 June 2022

Medicines fridgeThese case summaries are based on MDDUS files and are published here to highlight common pitfalls and encourage proactive risk management and best practice. Details have been changed to maintain confidentiality.


Ms K brings her three-year-old daughter Lucy to her GP surgery to receive her first vaccination for chicken pox.

She is seen by Dr M who has already removed the vial from the fridge before the child’s arrival. He draws up the vaccine in a separate room so as not to cause Lucy any alarm and then administers the injection without incident.

Dr M later begins to write up his clinical notes for the day. He checks the serial number of the vaccine he gave to Lucy and realises he has mistakenly given her an MMR vaccine instead of varicella. He notes that both vials are kept close together in the fridge, they are made by the same manufacturer and have similar packaging.

He immediately phones Ms K to inform her of the error and to apologise. He reassures her that no harm should come to Lucy because of the mix-up and that she should not experience any adverse side effects.

He asks Ms K if she would like to bring Lucy back that same day to have the chicken pox vaccine, but she decides to come back at a later date once she has had time to think about what has happened.

Dr M apologises again for the mix-up and adds that a significant event analysis (SEA) will be carried out to determine what went wrong and what measures can be put in place to prevent this from happening again.


Dr M calls an MDDUS medico-legal adviser (MLA) for advice on the next steps. In line with his duty of candour obligations, he plans to write to Ms K with more information about the incident and asks the MLA to review a letter he has drafted. He also asks whether it is advisable to share the results of the SEA with Ms K.

The MLA reviews and advises on the letter and agrees it would be appropriate to share the full details of the SEA investigation with Ms K.

She advises that the letter should acknowledge the shock and distress the error must have caused Ms K and reassure her that this error has been taken seriously. It should include an account of the investigation that has taken place and then continue with a factual summary of what happened. There should then be an apology for the error.

The MLA also advises Dr M to include in the letter information about the possible side effects or outcomes from an additional MMR vaccination, explaining how he obtained this information (e.g. by speaking to the local health trust or infectious disease specialist), and any advice with regards to the timing of the chicken pox vaccination.

The letter should then include a paragraph summarising what Dr M has learned from this incident and what changes he is making to prevent a similar incident from happening again.

The final paragraph of the letter should include an offer from Dr M to arrange a meeting to discuss this matter further in person should Ms K wish to do so.

With regards to the SEA, the MLA advises that the discussion about it should be carried out at a formal meeting, rather than in informal chats. Where possible, it would be useful to include a number of colleagues who are involved in vaccine administration (including non-medical colleagues) and encourage them to contribute to the process and learning outcomes.

The MLA suggests it may be useful for Dr M to acknowledge in the SEA discussion that he didn’t check the label on the vial when he removed it from the fridge, and that he also didn’t check its compatibility directly with the patient/parent. These are changes he will make to his vaccination process in future, as an extra safety check.

Dr M accepts that his concern over the child’s potential needle phobia – which led him to draw up the vaccine in a separate room – may have been counter-productive and may have contributed to the error.


  • If you discover an error, act quickly to notify the patient (or their representative), explaining what went wrong and offering an apology.
  • Ensure clinical processes for administering vaccines or other medications include sufficient safety checks, particularly relating to the type of vaccine/drug being administered and its appropriateness for the patient.
  • Involve relevant team members in formal discussions when conducting a significant event analysis.
  • Read MDDUS advice on duty of candour.

This page was correct at the time of publication. Any guidance is intended as general guidance for members only. If you are a member and need specific advice relating to your own circumstances, please contact one of our advisers.

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