Interventions
FLU
Parents of eligible children at practices in the intervention arm were sent the behaviourally-informed invitation letter by post with minimal local adjustments (e.g. reflecting the sender and flu clinic booking arrangements). A number of behavioural techniques were used, several of which were coded according to the Behavioural Change Technique (BCT) Taxonomy [Other behavioural techniques that were used included framing the message as a gain (Behavioural-science informed changes to the flu invitation letter and their rationaleThe letters were sent centrally by the Child Health Information System (CHIS) team on behalf of the practice between 21 and 25 October 2016.Parents of eligible children registered at general practices in the control arm were only provided with the usual communication from their practice. GPs are contracted to call and recall for immunizations. The National Institute of Health and Care Excellence (NICE) recommends contacting people for immunisations by a variety of methods, including text messages, letters, emails, phone calls from staff or an auto dialler, social media, or a combination of methods, as well as informing and inviting people during face-to-face interactions whenever the opportunity arises [We surveyed the GP practices to obtain information on their invitation communication with parents; 25% (63 out of 257) practices responded to the survey. The majority of practices confirmed that they had invited all eligible patients (76%), 17% to some parents and only one practice to no parents. Whilst the majority of practices reported sending letters to some or all parents, practices also used phone calls, text messages and opportunistic occasions. Recall was however less frequently undertaken by practices.