Limits of the Social-Benefit Motive among High-Risk Patients: A Field Experiment on Influenza Vaccination Behaviour

"...an emphasis on self-protection may be more successful in increasing vaccination than an emphasis on its social benefits..."

Influenza vaccine uptake remains low worldwide, inflicting substantial costs to public health. One strategy for strengthening intentions to vaccinate is harnessing prosocial motives (e.g., care for family, friends, and community) by recommending that health professionals highlight the social benefits of vaccination. This study examines whether the prosocial vaccination hypothesis applies to actual vaccination behaviour of high-risk patients.

Between November 2016 and March 2017, one of the researchers, an infectious disease physician, recruited in-patients on the day of their discharge from a tertiary care public hospital in Istanbul, Turkey. By selecting the next vaccine promotion pamphlet on the top of a previously shuffled stack, patients were randomly assigned to one of two treatment groups, including either the self-benefit (n=125; 51%) or the social-benefit message treatment (n=119; 49%).

The pamphlets were modelled after actual vaccine promotion messages used by the United Kingdom (UK) National Health Service. The top halves of the two pamphlets, which were the same, listed the objective risk group criteria and stated that influenza can have serious complications especially for someone in the risk group. At the bottom half, the text in the self-benefit treatment indicated that one can gain immunity against influenza by getting the vaccine, while the text in the social-benefit treatment in addition stated that gaining immunity would lower the chances of transmitting the disease to others. Prompts of "protect yourself" vs. "protect those around you" and corresponding emoticons were added to increase the salience and the clarity of each message.

Participants who decided to receive the free vaccine were vaccinated on site at the end of the study, which comprised the primary outcome measure. (The researcher recommended the vaccine only if asked for her advice (30%).) In addition, participants were given a free vaccination ticket that could be used by patient's family and friends within 2 weeks. This was intended to explore whether social networks can boost vaccination beyond the hospital setting.

Perceived risk has been shown to be a more powerful predictor of vaccination than objective risk. Thus, the study also compared objective (medically diagnosed) and subjective (patient-perceived) measures of risk group status, indicating high or low risk of severe harm due to influenza-related illnesses. Thus, after the elicitation of vaccination decision, a second questionnaire measured perceptions for being in the high-risk group (i.e., subjective risk); patients were categorised as at high objective risk through medical assessment based on the criteria set out by the Turkish Ministry of Health (e.g., elderly people or those with various chronic illnesses). This questionnaire also measured reasons for accepting or refusing vaccination.

Among 222 patients who were not vaccinated for the season prior to the study (72% medically assessed to be at high risk), 42% in the self-benefit frame chose to receive a vaccination compared with 34% in the social-benefits frame, but the difference was not statistically significant (adjusted odds ratio (aOR)=1.63, 95% confidence interval (CI) 0.90 to 2.95, p=0.108). Among 72 patients who sought and received the doctor's recommendation, 47 chose to receive vaccination (65.3%), in comparison to 38 of 150 (25.3%) patients who did not seek recommendation.

Exploratory analysis showed that the effect of messages depended on patient perception of risk group membership. While objective risk group membership did not moderate the effect of the messages on vaccine uptake, emphasis on self-benefit was more influential among patients who perceived themselves to be in the risk group (aOR=6.22, 95% CI 1.69 to 22.88, p=0.006). This is consistent with both empirical evidence that high risk perceptions motivate preventive health behaviour such as vaccination and with theoretical evidence that self-focused message will be affectively more salient for those with higher perceptions of risk group membership.

Reasons for vaccination focused primarily on self-benefit (67%) rather than social-benefit (5%). Among those who decided not to receive the vaccine, the most common reasons for rejection were found to be "self-confidence" such as "I never catch the flu" (26%), "current health conditions" such as receiving other treatments (26%), "vaccine mistrust" (15%), and "lack of experience or knowledge regarding the vaccine" (14%). Although "self-protection" was a more prevalent reason in the self-benefit (61%) than in the social-benefit treatment (39%), no statistically significant difference due to experimental manipulations was observed for any category in either acceptance or refusal reasons.

As a consequence of the intervention, 85 of 222 (38%) patients who were not yet vaccinated for the flu season chose to receive vaccination. Including the 22 participants who were already vaccinated at the start of the study, rate of vaccination by the end of the study was 44%. These values indicate substantial improvements over previous year rate of 16% vaccination among all 244 study participants, as well as over the 2006 vaccination rates of 6-19% among high-risk groups in Turkey.

However, not a single one of the 244 free vaccination tickets were brought back to the hospital to receive free vaccination. The researchers conjecture that patients either failed to pass the tickets on to others or when they did, they failed to persuade others to vaccinate. Either of these cases can be interpreted as evidence against strong prosocial motives in vaccination among a high-risk group.

In contrast to the literature observing intentions of low-risk populations, this study found no evidence that social-benefit motivates actual vaccination behaviour among a high-risk patient population. Instead, those who self-categorise as being in the high-risk group are more motivated by the self-benefit message. The results suggest that a stratified approach can improve coverage: Even if an emphasis on social-benefit could be effective among low-risk groups, an emphasis on self-benefit holds more promise for increasing vaccination in medical organisational settings where high-risk groups are prevalent. They therefore suggest that heterogeneity of risk groups and their perceptions should be taken into account when formulating vaccine advocacy policies.