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

Abstract

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.

Keywords: Conspiracy beliefs; Persuasion; Political communication; Public health communication; Survey experiment; Vaccine hesitancy.