Starting a health investment does not guarantee completing it. Parents may accept a first vaccine dose yet fail to return because they must remember, choose a feasible time, coordinate the visit, and act after a delay. This intention–action gap is especially relevant for multi-dose vaccination schedules.
The study compares two behavioral approaches. An ownership reminder says that a vaccine is reserved for the recipient, potentially making noncompletion feel like giving up something already assigned. A planning prompt instead suggests a concrete day and time, making an occasion for action focal without assigning an appointment or restricting alternatives.
A time-specific planning prompt raised HPV second-dose completion by 8.67 percentage points, compared with 4.58 points for an ownership reminder; the three treatments containing a planning prompt were statistically indistinguishable.
How the study worked
The researchers randomized 5,907 parent records, each linked to one girl aged 9–17 who had received a first HPV dose but had not completed the schedule, into six groups: pure control, unrelated-message placebo, ownership reminder, planning prompt, and two combined treatments with an ownership reminder 24 hours or two hours before the suggested time. Randomization was blocked by location and age group and balanced further on insurer and health-system characteristics.
The six-week SMS campaign ran from May 4 to June 11, 2022. Completion through July 30 was measured for the full randomized sample in Bogotá’s administrative vaccination registry. The estimates are intention-to-treat effects because message delivery and reading were not observed.
Results
All four active messages increased completion relative to the 8.63% pure-control rate. The ownership reminder added 4.58 percentage points, the planning prompt 8.67 points, and the combined treatments 7.94 and 9.10 points. A direct test rejects equality between ownership and planning (p=0.010), while the three planning-containing arms are statistically indistinguishable (p=0.778).
The gains emerged during the campaign and persisted through the end of follow-up. Under a common campaign-wide cost assumption, the planning prompt cost an estimated US$0.38 per additional second-dose completion, compared with US$0.72 for the ownership reminder.
What can we learn?
The ranking is consistent with planning and implementation frictions being more binding than entitlement frictions among families already at the completion margin. It does not directly identify the psychological mechanism: responses may also reflect how parents interpreted the messages or whether the suggested time fit their schedules.
The evidence applies to families who had already initiated HPV vaccination. It does not show that planning prompts increase first-dose take-up, overcome vaccine refusal or supply constraints, or improve cancer outcomes. The cost figures cover SMS and personnel within existing infrastructure, not vaccine provision, household costs, capital investment, or the full social cost of vaccination.
Findings
- Planning roughly doubled completion The planning prompt increased second-dose completion by 8.67 percentage points relative to a pure-control rate of 8.63%, an increase of about 100% over the control mean.
- Ownership helped, but less The ownership reminder increased completion by 4.58 percentage points, about 53% over the control mean. The planning effect was significantly larger (p=0.010).
- Combining messages added no detectable gain Combined planning and ownership messages increased completion by 7.94–9.10 percentage points, but their effects were statistically indistinguishable from planning alone (p=0.778).
- The direct implementation cost was low The planning prompt cost an estimated US$0.38 per additional completion under the study’s common cost assumption, versus US$0.72 for ownership; these are communication costs within existing infrastructure.
From evidence to action
Turn intentions into a concrete occasion
Where registries identify incomplete schedules, health authorities can test time-specific prompts that make a feasible return visit salient without imposing a formal appointment.
Prefer the simpler message unless added content proves useful
Adding an ownership reminder did not improve on planning alone in this setting and created a second contact in the combined arms. Simpler messages may therefore be a useful starting point for implementation.
Test fit and mechanism before scaling broadly
Future work should let families choose a time, compare suggestions with formal appointments, observe message delivery, and measure planning constraints directly before extending the intervention to first-dose take-up or other settings.
Abstract
Failure to complete vaccination schedules represents an important form of health underinvestment in developing economies. We study this problem in the context of HPV vaccination in Colombia, where many girls initiate but do not complete the schedule. Messages framing a vaccine as reserved for the recipient can increase uptake, but they may be less effective when the relevant barrier is planning rather than entitlement. We test this hypothesis in a randomized controlled trial with parents of girls located inside and outside Bogota who had initiated but not completed HPV vaccination. The experiment compares ownership reminders with time-specific planning prompts: messages suggesting a specific day and time for vaccination without assigning an appointment or changing the formal choice set. The planning-prompt treatment and the combined treatments increase second-dose completion by 7.94 to 9.10 percentage points, relative to 8.63 percent in the control group, while the ownership reminder increases completion by 4.58 percentage points. This ranking is consistent with planning and implementation frictions being more binding than entitlement frictions among marginal households, although the experiment does not directly measure these mechanisms.
Peña, Julian, and Stanislao Maldonado. 2026. "Planning frictions and the incomplete take-up of health investments: The case of HPV vaccination." BEER Lab Working Paper BEER-WP-2026-03, Tecnológico de Monterrey.
Research team
Julian Peña and Stanislao Maldonado. Julian Peña is at Universidad del Rosario and Stanislao Maldonado is at Tecnológico de Monterrey. The intervention was developed and implemented with support from public-health and research partners in Colombia and internationally.