Results
ADVERSE EVENTS, RECRUITMENT, INFLUENZA
Overall, 2831 children were screened for the trial; 2212 were deemed ineligible including prior receipt of influenza vaccine before study start, leaving 619 who were randomly assigned to the intervention and control groups. After randomization, 19 participants were excluded because they had already received the 2021 influenza vaccine (n = 17) or had a medical contraindication (n = 2). A further 19 children were ineligible due to age younger than 6 months (n = 2) or 18 years or older (n = 17) at the time of randomization; however, as they were deemed otherwise eligible for influenza vaccination, they were retained in the intention-to-treat analyses.Hence, 600 participants (intervention group: 298 [49.7%]; mean [SD] age, 11.5 [4.6] years; 162 female participants [54.4%]; 136 male participants [45.6%]; control group: 302 [50.3%]; mean [SD] age, 11.4 [4.7] years; 155 female participants [51.3%]; 147 male participants [48.7%]) completed the study. Analysis was by original assigned groups. The recruitment and randomization period was April 15 to August 13, 2021. There were no adverse events. Participants in the trial arms did not substantially differ by age, sex, Aboriginal or Torres Strait Islander or non-Indigenous status, medical risk group, Index of Relative Socioeconomic Disadvantage, or residential location. Only 12 parents (4%) opted out of the SMS messaging. Across both 2019 and 2020, there was a higher proportion of children vaccinated for influenza in the intervention group (