Effect of Information about COVID-19 Vaccine Effectiveness and Side Effects on Behavioural Intentions: Two Online Experiments

"The clear and transparent communication of COVID-19 vaccines' risks and benefits has been suggested as an approach to increasing vaccine uptake among the general public ..., a means of maintaining public trust in science..., and also as an ethical imperative."

A sizable minority of people around the world express hesitancy towards taking COVID-19 vaccines. Concerns over safety and efficacy may be fuelled by COVID-19 vaccine misinformation. Many public health commentators and researchers have called for transparent communication of COVID-19 vaccine information to improve vaccine uptake. Vaccinations do not offer full immunity, which creates a dilemma for communicators who wish to be transparent about benefits and harms and encourage continued caution in vaccinated individuals but not undermine confidence in vaccination. In order to inform debates about how to boost uptake, researchers conducted two experiments to generate empirical data on the effects of real-world communications being carried out by various public health authorities, whether they are attempting to inform or persuade.

In two online pre-registered experimental studies on quota-sampled United Kingdom (UK) public participants, the researchers investigated the effects of providing transparent communication - including uncertainty - about vaccination effectiveness on decision-making.

Study 1 (n = 2,097) examined the effects of reading comprehensive information from recent clinical trials (in two different formats) on individuals' intentions to receive a vaccine. In addition, this study includes outcome measures examining: participants' belief that COVID-19 vaccines are effective, concern over side effects, and concern over speed of regulatory approval (using the Oxford COVID-19 Vaccine Beliefs Scale). This study also includes two further exploratory messages as experimental conditions: The first focuses on addressing concerns over the speed of vaccine development and approval, which is also associated with vaccine hesitancy; the second presents a mechanistic description of how vaccines, including the new mRNA vaccines, work (mechanistic explanations have been shown to reduce risk perceptions and shift attitudes in other scientific domains).

In short, study 1 found that detailed information about COVID-19 vaccines does not have a significant impact on beliefs about the efficacy of such vaccines, concerns over side effects, or intentions to receive a vaccine. However, some messages increased participants' reported awareness of the risks and benefits, with participants feeling informed regarding their vaccination decision relative to those in the control group. (Results of analyses focusing on ratings of the information (e.g., trustworthiness, believability, and ease of understanding) are reported in Supplementary Material 3.)

Study 2 (n = 2,217) addressed concerns that highlighting the need to maintain protective behaviours (e.g., social distancing) post vaccination may lower perceptions of vaccine efficacy and willingness to receive a vaccine. It expressed high uncertainty about vaccine efficacy (a range of "41-98%") and reminded the reader that protective behaviours would need to be maintained even once vaccinated. Six different messages were developed, modelled on existing communications from UK public health bodies, designed to vary in the emphasis they put on uncertainty about the efficacy of vaccines and the need to continue protective behaviour once vaccinated.

In short, study 2 found that transparent messages did not significantly reduce perceptions of vaccine efficacy, and in some cases (simple claims that vaccines are safe and effective) increased perceptions of efficacy. "This will be of some comfort to public health communicators concerned that calls to continue social distancing and mask-wearing once vaccinated...might undermine perceptions of vaccine efficacy."

Thus, the experiments found that "intention to receive a vaccine when offered is relatively high and that different messages - ranging from detailed tables of vaccine efficacy and side effects to a simple claim that vaccines are safe and effective - do not substantially increase intentions to receive a COVID-19 vaccine." There was also no evidence that such communications lead to a decrease in vaccination intentions either ("backfire effects").

Possible future research and practice directions include:

• Testing message framings that focus on prosocial or collective benefits of vaccination, which may be especially relevant for increasing vaccination rates in younger age groups who are at lower risk of death or hospitalisation from COVID-19 and perceive less threat from the virus.
• Examining the impact of message source: It is possible that attributing the information to a source considered trustworthy by the UK public (e.g., the National Health Service - NHS) may have increased the impact of information.
• Undertaking interventions such as targeting messaging specifically to hesitant groups, working with trusted community leaders, training healthcare workers for face-to-face conversations with vaccine-hesitant individuals, and reducing financial or logistical barriers (e.g., access to vaccination sites).

Taken as whole, the results "align with the wider research on non-COVID-19 vaccine messaging, which indicates that simple written or visual purely informational messages have limited effects on vaccine hesitancy and uptake..." The results are consistent wtih Opel et al.'s argument that vaccine hesitancy is not simply due to "a deficit of the data needed to make an informed decision." However, while the studies "do not provide a strong basis for public health authorities to communicate vaccine information with the aim of increasing uptake of the vaccine,...governments and responsible public health bodies have an ethical duty to inform the public of the risks and benefits of the vaccines they are asking the public to take....Such transparent communication may also serve to build trust over the longer term..."