The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been endorsed by the ANZCTR. Before participating in a study, talk to your health care provider and refer to this information for consumers
Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Prospectively registered

Titles & IDs
Public title
The Effect of Short Message Service (SMS)-Reminders on Vaccine Hesitancy in New Parents
Scientific title
The Effect of SMS-Reminders on Vaccine Hesitancy in New Parents
Secondary ID [1] 295936 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Childhood preventable infections 309441 0
Condition category
Condition code
Infection 308284 308284 0 0
Other infectious diseases
Public Health 308368 308368 0 0
Health promotion/education

Study type
Description of intervention(s) / exposure
Intervention: SMS-Reminder to New Parents
Method: Delivered via phone through mass SMS services.
Timing: 6 weeks post-natally, prior to their child's 6-8 week vaccination. Interventional SMS only sent once.
1) Group A (intervention): Telethon Kids health message: Your child is now due for their 2 month vaccination. Delaying a child’s vaccination can put them and other children at risk. Do not reply to this text message
2) Group B (control): Telethon Kids health message: Sleeping your baby on its back is safest for preventing SIDS (Sudden Infant Death Syndrome). Do not reply to this text message
Intervention code [1] 312260 0
Intervention code [2] 312261 0
Comparator / control treatment
The control group receives the SMS at the same time as the treatment group however, the contents differ. The SMS sent to this group is around prevention of SIDS, not vaccinations.
Control group

Primary outcome [1] 307255 0
Change in Vaccine Hesitancy Category as measured by PACV Short Scale
- Low Hesitancy (score 0-4)
- Medium Hesitancy(score 5-6)
- High Hesitancy (score 7-10)
Timepoint [1] 307255 0
Hesitancy questionnaire administered 4 weeks before intervention and 6 weeks after intervention.
Change in score on the questionnaire (and hence category) evaluated.
Secondary outcome [1] 351292 0
Timepoint [1] 351292 0

Key inclusion criteria
1. Parent(s) are expecting their first child
2. Parent(s) are above the age of 18
3. Parent(s) are English speaking (primary or secondary)
4. Mother is > or equal to 28 weeks pregnant
5. Parent(s) have a mobile phone with text messaging and data/wifi connection capabilities
6. Parent(s) are able to be contacted via mobile phone during the course of the study.
Minimum age
18 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
1. Parent(s) who are unsuitable for the study as advised by clinic staff
2. Parent(s) suffer from a condition that interferes with their ability to give informed consent and/or comply with the study
3. Parent(s) with a baby born <36 weeks.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Central randomisation through computer program.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using randomisation process created by computer software
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
Sample size: A sample size of 274 participants (137 per invention arm) is required to detect at least a 30% reduction in the proportion of participants categorised as low vaccine hesitancy (score 0-4 out of 10) on the PACV short scale. This is based on: (i) expected proportions of low, medium and high vaccine hesitancy in the control arm of 72%, 13% and 15%, respectively11; (ii) 30% change from low to medium vaccine hesitancy category for the SMS intervention arm (thus the proportions for the low, medium and high categories would be 50%, 35% and 15%, respectively); (iii) significance level (a) of 5%; (iv) power of 80%; (v) equal allocation to intervention arms; and (v) sample size formula for the Wilcoxon-Mann-Whitney test by Zhao et al

Statistical Methods:
Demographic and other baseline characteristics will be summarised by assigned intervention arm (intent-to-treat). Categorical variables will be summarised by frequencies and percentages. Continuous variables with symmetric distributions will be summarised by intervention arm using mean and standard deviation, whereas continuous variables with asymmetric distributions will be summarised using median and interquartile range (25% and 75% percentiles).

PACV short scale category (ie. low, medium, high vaccine hesitancy) at the 12 week post-natal timepoint (primary outcome) will be compared between the negative-message SMS and control SMS arms using the Wilcoxon-Mann-Whitney test. The use of low, medium and high vaccine hesitancy categories will aid interpretation of the results, however, the individual scores for the PACV short scale will also be analysed using the Wilcoxon-Mann-Whitney test. Results from both analyses will be presented with approximate 95% confidence intervals and associated p-values.

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 11747 0
King Edward Memorial Hospital - Subiaco
Recruitment postcode(s) [1] 23831 0
6008 - Subiaco

Funding & Sponsors
Funding source category [1] 300534 0
Other Collaborative groups
Name [1] 300534 0
Telethon Kids Institute
Address [1] 300534 0
Northern Entrance, Perth Children's Hospital,
15 Hospital Ave, Nedlands Western Australia 6009
Country [1] 300534 0
Primary sponsor type
Other Collaborative groups
Telethon Kids Institute
Northern Entrance, Perth Children's Hospital,
15 Hospital Ave, Nedlands Western Australia 6009
Secondary sponsor category [1] 300018 0
Name [1] 300018 0
Address [1] 300018 0
Country [1] 300018 0

Ethics approval
Ethics application status
Ethics committee name [1] 301327 0
Women and Newborn Health Service Ethics Committee,
Ethics committee address [1] 301327 0
374, Bagot Road. Subiaco.
Western Australia. 6008.
Ethics committee country [1] 301327 0
Date submitted for ethics approval [1] 301327 0
Approval date [1] 301327 0
Ethics approval number [1] 301327 0

Brief summary
The current vaccination rates for Australian children under the age of five are below the national target of 95% coverage, which is required to achieve herd immunity. Herd immunity is a pattern of immunity where the risk of an individual contracting an infection is reduced by having vaccinated or immune individuals surrounding them, hence protecting against infectious diseases such as measles and smallpox. The low vaccination rates can be attributable to vaccine hesitancy which is the delay in acceptance of a vaccine despite availability. This behaviour occurs on a spectrum and is influenced by various factors.
A novel way to reduce vaccine hesitancy is by implementing strategies informed by the field of behavioural economics through SMS technology. This single blinded randomised controlled trial will enrol up to 274 new parents from King Edward Memorial Hospital. Participants will be randomised into two groups, both receiving a vaccine hesitancy survey before and after the intervention (an SMS reminder.) The outcome will be measured through a change in the vaccine hesitancy score, calculated from survey responses.
The primary objective of this study is to examine the effect of negative SMS vaccine reminders on vaccine hesitancy in new parents.
Trial website
Trial related presentations / publications
Public notes
Attachments [1] 3050 3050 0 0
Attachments [3] 3052 3052 0 0
Attachments [4] 3053 3053 0 0

Principal investigator
Name 86630 0
A/Prof Thomas Snelling
Address 86630 0
Telethon Kids Institute
15 Hospital Ave, Nedlands WA 6009
Country 86630 0
Phone 86630 0
+61 8 6319 1817
Fax 86630 0
Email 86630 0
Contact person for public queries
Name 86631 0
Ms Mudra Shah
Address 86631 0
Telethon Kids Institute
15 Hospital Ave, Nedlands WA 6009
Country 86631 0
Phone 86631 0
Fax 86631 0
Email 86631 0
Contact person for scientific queries
Name 86632 0
Ms Mudra Shah
Address 86632 0
Telethon Kids Institute
15 Hospital Ave, Nedlands WA 6009
Country 86632 0
Phone 86632 0
Fax 86632 0
Email 86632 0

No data has been provided for results reporting
Summary results
Not applicable