This site is optimised for modern browsers. For the best experience, please use Google Chrome, Mozilla Firefox, or Microsoft Edge.


We welcome your feedback, which will help improve this site.

Feedback form

Case study: Safety of nasal influenza immunisation in egg-allergic children

The SNIFFLE and SNIFFLE-2 studies were NIHR studies under the Children and Young People specialty.

Find out more


Influenza (flu) immunisation has been recommended in the UK since the late 1960s to reduce the spread of the infection and protect people in high-risk groups, for whom flu may prove to be serious or fatal.

A flu vaccine known as LAIV (Live Attenuated Intranasal Vaccine) has recently been approved by a number of licensing boards. The Joint Committee on Vaccination and Immunisation recommends LAIV as the flu vaccine of choice for two reasons: it has been found to be the most effective vaccine available; and it is administered through a nasal spray which is preferable to parents and children than an injection.

LAIV is grown in hens’ eggs which means that it can contain egg protein. Egg allergy is one of the most common food allergies in early childhood and affects at least one in 50 preschool children. It is recommended that children between two and 17 years old receive the flu vaccine and before the SNIFFLE studies, egg allergic children were referred by the NHS to secondary care for flu immunisation.

Outcomes and findings

  • Egg allergy is one of the most common food allergies in children
  • The current influenza (flu) vaccine can contain egg protein which means that until recently egg-allergic children were referred to secondary care for immunisation
  • The two SNIFFLE studies vaccinated 1,061 egg-allergic children with the current flu vaccine and observed them afterwards.
  • Both studies were multicentre trials, across 14 and 29 sites respectively. The NIHR provided the framework for this multicentre approach and supported local sites
  • The Chief Investigators are Dr Mich Lajeunesse (Southampton Children’s Hospital) and Dr Paul Turner (Imperial College London)

The SNIFFLE studies aimed to determine whether LAIV was safe for use on children with an egg allergy. Researchers immunised egg allergic children with the vaccine, observed them for two hours afterwards and followed this up with a phone call after three days to assess for any adverse effects. The SNIFFLE-2 study also followed up after one month to check for any effect on asthma control. In total across the two studies, 1,061 egg-allergic children were vaccinated.

Value to the NHS

The SNIFFLE and SNIFFLE-2 studies led to a change in national immunisation policy. The results were presented to the Joint Committee on Vaccination and Immunisation and on the basis of the data, LAIV is now permitted to be administered to children with an egg allergy. This means that egg allergic children now receive the vaccine in primary care or schools as part of the national immunisation programme. The studies have led to considerable cost savings for the NHS by reducing referral to secondary care for flu immunisation in egg allergic children.LAIV is not currently recommended for children and adolescents with severe asthma or active wheezing. The research is continuing with SNIFFLE-3 and SNIFFLE-4 studies investigating the safety of LAIV in children with pre-existing asthma.

The SNIFFLE studies have made it possible for egg-allergic children to receive the LAIV nasal flu vaccine safely
Dr Mich Lajeunesse, Consultant in Paediatric Allergy and Immunology (Southampton Children's Hospital) and Co-Chief Investigator for SNIFFLE and SNIFFLE-2

Key publications

Turner PJ, Southern J, Andrews NJ, Miller E, Erlewyn-Lajeunesse M; SNIFFLE Study Investigators. Safety of live attenuated influenza vaccine in atopic children with egg allergy. J Allergy Clin Immunol. 2015 Feb 1 PMID: 25684279.

Turner PJ, Southern J, Andrews NJ, Miller E, Erlewyn-Lajeunesse M; on behalf of the SNIFFLE-2 Study Investigators (2015) Safety of Live Attenuated Influenza Vaccine in Children with Egg Allergy: a multi-centre, non-randomised intervention study. BMJ. 2015 Dec 8;351:h6291 PMID 26645895