Completion points and defaults to increase HPV vaccinations

Completion points and defaults to increase HPV vaccinations


According to the Ministry of Health and Social Protection, cervical cancer is the leading cause of death from cancer among women aged 30 to 59 years in Colombia. Unlike many other cancers, this type is mainly caused by a virus: the Human Papilloma Virus (HPV), which can be transmitted through oral, vaginal, or anal sexual contact. The prevalence of HPV in Latin America and the Caribbean is 16%, the second highest in the world after countries in Sub-Saharan Africa (24%). Fortunately, the risk of HPV infection and the risk of developing this type of cancer can be prevented through a vaccine administered free of charge in Colombia to girls and adolescents between the ages of 9 and 17. However, HPV vaccination coverage in Bogotá is lower than expected, and only 6% of 9-year-old girls are fully inoculated with two doses of the HPV vaccine.

The Project

To increase the HPV vaccination rate in Bogotá, the Behavioral Economics Group sent text messages with behavioral economics principles to parents of girls between 9 and 17 years, in coordination with the Secretariat of Health of Bogotá, the Ministry of Health of Colombia, the American Cancer Society (ACS), the Liga Colombiana Contra el Cáncer and the Behavioral Government Lab at Universidad del Rosario. The complete intervention targeted a total of 174,181 parents. From that sample, 75% were nudged to vaccinate their daughters for the first time, while the rest were parents of girls and adolescents pending one vaccine who were reminded to complete the entire vaccination scheme of two doses. This project summary presents one out of the six experiments run during the whole project. The intervention took place between October 2021 and December 2021.

Behavioral Barriers:

Salience: Our attention is limited. Therefore, behavioral economics interventions carefully consider the moment when a message is delivered, the location in which it is delivered, and the content it emphasizes. In this context, parents are unsure when they should vaccinate their daughters against HPV and wait for the doctors to recommend vaccination. However, all the doctors interviewed reported limited time during appointments, and more urgent issues took priority over HPV. The absence of discussions and reminders leads parents to assume passive attitudes toward HPV vaccination. In general, there is a lack of moments of reflection, choice, and opportunity to take action on HPV vaccination for girls aged 9-17 in Bogotá.

Mental accounting: Mental accounting is our tendency to mentally sort our money into separate “accounts,” leading us to see money as less fungible than it is and affecting our spending behavior. The concept is usually applied to personal finances, but in this context we apply it to the use of time and activity.  In the case of children’s vaccines, although the vaccine is part of the full vaccination scheme, parents do not put the same amount of effort into vaccinating their daughters against HPV as for other vaccines deemed “more essential.” Evidence from our interviews indicates that parents mistakenly view vaccination as no longer a significant priority in children's health considerations after five years of age. 

Mistrust: Mistrust occurs when one party is unwilling to rely on the actions of another party in a future situation. Government support for the HPV vaccine has waxed and waned in the past, adding complexity to parents’ decision to vaccinate their daughters. Health professionals believe that a more explicit endorsement from the government would increase trust and make parents more likely to accept the vaccine recommendation. Parents interviewed in the diagnostic phase of our study expressed their desire for the government to take a more explicit stance on their support of HPV vaccinations.

Present bias: Present bias, associated with a preference for instant gratification, is the tendency to opt for a lesser benefit in the short term over a greater benefit in the longer term. Because immunity is not tangible, it is difficult to appreciate the benefits of vaccination in the short term. In addition, there is no immediate consequence for failing to receive the HPV vaccine; this stands in contrast to, for example, the requirement of certain immunizations for children 0-5 years in order to be admitted to school. It thus becomes easy to put off the decision about HPV vaccination to the future.

Behavioral Tools:

Information: Although the full vaccination scheme of two doses is administered at no cost to families, some parents we interviewed were unsure about the vaccine’s cost and mentioned that the vaccine’s cost was preventing them from vaccinating their daughters. In this project, we informed parents that vaccinating their daughters is free.

Altruism: Disinterested and selfless concern for the well-being of others. The consequence of vaccinating or not vaccinating a daughter is faced by her and not by her parent. Therefore, we encourage parents to vaccinate their daughters, emphasizing that it is a way to protect their daughters.

Framing: The way information is presented can have a big impact on people’s understanding of it, and on the actions they take. For example, highlighting the negative aspect of a decision can cause an option to be perceived as more—or less—attractive. In this experiment, we varied the ways that we presented the status quo (inaction) and its consequences, for example, by defaulting the parent into a vaccination appointment or allowing them to choose to run a risk on behalf of their daughter and finally by changing their perception of the set of most essential immunizations.

Enhanced-active choice: This communication design is based on posing a question related to willingness to take the desired action and presents response options. Usually, these designs present response options highlighting losses inherent in the non-preferred alternative. In one of our treatments, our enhanced active choice design posed the question to parents about their willingness to vaccinate their daughters and presented them with an option that highlighted the negative consequence of not doing so (cancer).

Defaults: Defaults are the automatically preset courses of the desired action and are effective when the individual making the decision does not change them. This tool generally addresses cognitive overload or present bias, supported by our tendency to maintain the status quo. Given that we tend to stick to the status quo, changing it for the better can have a significant impact on behavior. We told parents that they had an appointment to vaccinate their daughters on a specific date to set the action of vaccinating their daughter as the default.

Pseudo-sets (framing): It refers to the arbitrary grouping of items or tasks together as part of an apparent “set” that motivates people to reach perceived completion points. By reminding parents of the number of vaccines their children need to complete their vaccination scheme and by pointing out that the HPV vaccine was missing to complete that scheme, we leveraged their need for completion.

Intervention Design

The Behavioral Economics Group, in coordination with the Secretariat of Health of Bogota, the Ministry of Health in Colombia, La Liga Colombiana Contra el Cáncer, the American Cancer Society, and Universidad del Rosario, implemented several SMS experiments designed to increase HPV vaccination rates in Colombia. All the experiments were implemented through a text message campaign (SMS), differing in the behavioral tool used to prepare the message. Our team decided on this channel because the Secretariat of Health of Bogotá had already launched several SMS campaigns in the past. In this summary, we will explain one of those experiments based on content related to framing their perceived status quo and its consequences. 

Table 1. Message content by behavioral design tool

Table 1. Message content by behavioral design tool

Table 1 shows that this experiment included three behaviorally informed text messages and three control groups. The pure control group did not receive any message. The policy control group received the "business as usual" message that the Secretariat of Health in Bogota was using in communications with the target population. The experimental control group included fixed elements that were incorporated into every treatment. The fixed elements for this informational experiment were a customized greeting with the parent’s name, the Secretariat of Health’s signature, and information about the vaccine’s availability at no cost.  

The experiment consisted of sending a weekly text message to the target population’s parents over eight weeks. The content of the message remained constant. The vaccination records of the Secretary of Health are updated daily, and our team receives them weekly. This allowed us to remove those parents who had already taken action before sending the subsequent message.

This experiment targeted parents of girls that had never been vaccinated against HPV in the past, and the objective was to help them vaccinate their daughters for the first time. The number of parents who participated in this experiment was around 34,506. Table 1 shows the message by behavioral design tool used to design each message.


This project had several challenges:

  • Despite our team’s solid credentials, it took considerable effort to create rapport with government employees at the Secretariat of Health. Specifically, the Secretariat of Health’s ethics committee asked us to make significant revisions to our ethics materials, even though the project had already gone through the ethics committee at Universidad del Rosario.
  • Related to that, it was not easy or fast to get the correct data set from Secretariat of Health's records because it took time to synchronize our team’s needs with the correct data extraction from administrative records. 
  • Another obstacle was that the proposed government’s partner agency could not send the text messages, so we had to find an alternative platform to send SMS. We used a platform that we had previously worked with (Altiria), and our team programmed and sent the SMS. The upside is that we gained control over the experiment. However, we lost the opportunity to train government officials on these interventions. 
  • HPV vaccines ran out after week 4 of our intervention in some vaccination centers. We had to stop sending SMS and helped in the coordination between the Ministry of Health and the Secretariat of Health. They quickly responded, and we were able to resume the experiment after pausing it for ten days. 


Results indicate that the SMS intervention increased first-time HPV vaccination rates in Bogotá.

  • The most impactful treatment to increase first-time vaccinations was pseudo-sets. This group had an average vaccination rate of 7.3%, representing a 32% difference compared to the control group (vaccination group average of 5.5%). This difference was statistically significant at the 1% level.
  • Very closely behind was the effect of the soft-default treatment. This group had an average vaccination rate of 7.2%, representing a 29% difference compared to the control group (vaccination group average of 5.5%). This difference was statistically significant at the 1% level.
  • Altruism has an average effect of 6.9%, representing a difference of 24% compared to the control group, suggesting that this simple message can be better than not sending a message. This difference was statistically significant at the 1% level.  
  • The policy control had an average vaccination rate higher than the pure control; however, it was not statistically significant. This means that one cannot claim that the policy control is better than no message.

Figure 1. Pseudo-sets and Soft-defaults were the most effective messages at getting parents to vaccinate their daughters for the first time

Figure 1. Pseudo-sets and Soft-defaults were the most effective messages at getting parents to vaccinate their daughters for the first time

Policy implications

  • Governments already have the capability to launch text message campaigns in-house, and they already count on the data and human capital to design these messages; thus, the implementation of behaviorally informed communications campaigns is low-hanging fruit.  
  • Since humans inherently feel a need to complete cycles, governments should keep reminding parents about the number of vaccines they need and about their pending vaccines to reach the required number, especially when it is only one vaccine that their children need to complete their scheme.

To mobilize parents to visit vaccination sites, an artificial appointment can create a need to follow through, attend the appointment, and vaccinate their children. However, this is effective only if vaccine availability is guaranteed. Otherwise, this could have a detrimental effect by furthering distrust and creating a bad reputation for the institution that is sending the message.