This will be an observational study where parents/ guardians of children in receipt of their preschool booster will be approached for their child(ren) to take part. Following written informed consent the Vaccine Research Nurse will explain the purpose of the study and what would be involved. Participation will involve completion of a health diary for the week following vaccination to document how their child has been both in terms of local reactions and systemic symptoms as well as any visits to a doctor (GP or hospital). The nurse will telephone the family at 48−72 hours following vaccination to see how the child has been. Information about the vaccine given in the current campaign and vaccines administered in the infant schedule including date of administration, product and batch number will be recorded where available.

Should any large local reactions be reported the nurse may visit the child to take a photograph to document and illustrate these - photographs will be taken without the child's face visible.

Subjects will be recruited in two centres - Hertfordshire and Gloucestershire. Recruitment will start as soon as the necessary approvals are in place. Monthly reports of observed data will be submitted to the MHRA though the formal analysis will not be conducted until the end of the study.

Recruitment figures and the incidence of ESLs will be reviewed on a six−monthly basis.

At this point it is difficult to predict parental attitude to taking part, though from experience with recruitment in previous studies it is hoped this will be positive, so affording a large number of participants.