Ethics approval and consent to participate
FLU
Study 1: Ethical approval: Health Research Authority, REC reference16/WS/0181.Study 2: Ethical approval: PHE Research Ethics and Governance Group, Reference number R&D 281.All methods were carried out in accordance with relevant guidelines and regulations. CONSORT reporting guidelines were followed (see the Supplementary Materials).Informed consent was obtained from the participating CCG’s within study 1. For study 2, informed consent was obtained from the participating childhood flu school vaccination providers.Study 2 was discussed with the PHE ethics committee who have stated that total informed consent from parents of the school children was not required due to the following reasons:Parents were expecting to receive a letter about the flu immunisation, so they were not getting anything unexpected.If parents had known ahead of receiving the letter that different letters were going to be sent this may have influenced the response of the parent to the letter and the researcher would not have got an accurate picture of how effective the different letters had been.Also it was necessary for all parents to be included in the study. Some may not have had time to give consent and it needed everybody to receive and react to their letter in order to see which worked best. If numbers had been too low there would have been insufficient study data to see an effect.