1 Department of Psychology, Université du Québec à Montréal, Montreal, QC, H3C 3P8, Canada; Montreal Behavioural Medicine Centre, CIUSSS du Nord- de- l'Ile- de- Montreal, Montreal, Québec, H4J 1C5, Canada.
2 Vaccine Uptake Group, Murdoch Children's Research Institute, Melbourne, VIC 3052, Australia; Clinical Epidemiology and Biostatistics Unit, Murdoch Children's Research Unit, Melbourne, VIC 3052, Australia.
3 Vaccine Uptake Group, Murdoch Children's Research Institute, Melbourne, VIC 3052, Australia; Department of Paediatrics, The University of Melbourne, The Royal Children's Hospital, Melbourne, VIC 3052, Australia.
4 Monash Centre for Health Research and Implementation (MCHRI), Monash University, Clayton, VIC 3168, Australia.
5 Montreal Behavioural Medicine Centre, CIUSSS du Nord- de- l'Ile- de- Montreal, Montreal, Québec, H4J 1C5, Canada; Department of Health, Kinesiology & Applied Physiology, Concordia University, Montréal, QC H4B 1R6, Canada.
6 Eastern Health Clinical School, Monash University, Box Hill, VIC 3128, Australia.
7 Vaccine Uptake Group, Murdoch Children's Research Institute, Melbourne, VIC 3052, Australia; Department of Paediatrics, The University of Melbourne, The Royal Children's Hospital, Melbourne, VIC 3052, Australia; Department of General Medicine, The Royal Children's, Melbourne, VIC 3052, Australia. Electronic address: margie.Danchin@rch.org.au.

Background: Despite COVID-19 infection being less severe in children compared to adults, vaccination for children from the age of 6 months onwards is recommended in many countries to reduce symptom severity and prevent severe disease. However, vaccination against COVID-19 for children remains controversial and uptake has been low.

Aims: To assess and compare the rate of change of parent-reported COVID-19 vaccine uptake in children aged 5 to 11 years and motivators of vaccine acceptance and non-vaccination among parents/guardians in Canada and Australia.

Methods: As part of the iCARE study, two cross-sectional representative samples in Canada and Australia were collected between May 20 and September 12, 2022 (i.e., 5 and 9 months after the COVID-19 vaccine rollout for children 5-11 years) using online panels. Parents/guardians reported the vaccine status of their children and motivators for vaccine acceptance and non-vaccination. General linear models were used to estimate differences between countries in terms of vaccine uptake and motivators across time.

Results: Parent-reported vaccine uptake for children 5-11 years didn't increase over the study period (T₁ = 87 %,T₂ = 86 %; OR = 0.83; 95 %CI = 0.45-1.54) and was overall lower in Canada (60.8 %) compared to Australia (71.6 %)(OR = 0.56; 95 %CI = 0.33-0.96). In both countries the socioeconomic characteristics of parents who didn't vaccinate their children were similar and having information on either the short- or long-term side effects of the vaccine were important motivators. However, vaccine effectiveness was more important in Canada and trust in the company that developed the vaccine and a recommendation from the child's doctor were more important motivators in Australia.

Conclusion: Parent-reported vaccine uptake for children 5-11 years plateaued early in the vaccine rollout. The main motivators for parents of unvaccinated children varied between the two countries but information on vaccine safety and effectiveness were common to both countries. Findings may inform future tailored vaccine communication efforts and pandemic planning in Australia and Canada to optimize vaccine uptake for primary school children.