Controversies of COVID-19 vaccine promotion: lessons of three randomised survey experiments from Hungary.

OBJECTIVES

This study aimed to investigate vaccine promotion messages, examine the heterogeneous effects of these messages and provide experimental evidence to help evaluate the efficiency of COVID-19 vaccine promotion campaigns in Hungary.

STUDY DESIGN

This study presents the results of three randomised survey experiments that were embedded in cross-sectional, representative, public opinion studies of Hungarian adults based on in-person interviews. Simple randomisation and blinding were applied to assign participants into the control group (no message) or treatment groups (vaccine promotion messages).

METHODS

The first experiment (March 2021) aimed to test vaccination promotion messages from politicians (N = 331) and medical experts (N = 342) by comparing experimental groups' trust in vaccines and conspiratorial beliefs with the control group (N = 327). The second experiment (September 2022) tested the impact of two communication strategies ([1] highlighting the safety and effectiveness of vaccines, N = 104; and [2] highlighting the wide variety of vaccines available, N = 110) on increasing vaccine uptake among those who were still unvaccinated (control group, N = 89). The third experiment (September 2022) tested one message aiming to increase COVID-19 booster uptake among those who received only the first round of vaccination (N = 172; control group, N = 169). The outcome variable in the second and third experiments was intent to get vaccinated. Robust regressions, logit models, Mann-Whitney U-tests and model-based recursive partitioning were run. The inference criteria (p < 0.05) was set in pre-registration of the experiments.

RESULTS

All treatment effects were insignificant, but exploratory research found significant conditional treatment effects. Exposure to vaccine promotion by medical professionals was associated with a higher level of trust in Russian and Chinese COVID-19 vaccines in older age cohorts (weighted robust regressions, 50-59 years old, Russian vaccine: +0.769, interaction term [i.t.] p = 0.010; Chinese vaccine: +0.326, i.t. p = 0.044; and ≥60 years old, Russian vaccine +0.183, i.t. p = 0.040; Chinese vaccine +0.559, i.t. p = 0.010) and with a lower level of trust in these vaccines among younger adults (<30 years old, Russian vaccine: -1.236, i.t. p = 0.023; Chinese vaccine: -1.281, i.t. p = 0.022). Receiving a vaccine promotion message from politicians led to a higher level of trust in Chinese vaccines among the oldest respondents (≥60 years: +0.634, i.t. p = 0.035).

CONCLUSIONS

Short-term persuasion attempts that aimed to convince respondents about COVID-19 vaccination were ineffective. Booster hesitancy, similar to primary vaccine hesitancy, was resistant to vaccine promotion messages. Significant conditional effects suggest that COVID-19 vaccine promotion by medical experts and politicians may have had adverse effects for some demographic groups in Hungary.