Vaccine effectiveness and side-effect profiles significantly influence recipients' preference for one vaccine over another, according to a new study. But those issues matter less to those who are vaccine-hesitant, the authors reported.

The study published in PLOS ONE involved hypothetical COVID-19 vaccines. Swiss researchers from the universities of Bern and Zurich and colleagues suggested that what influences perceptions of vaccines could help improve efforts to combat vaccine hesitancy during the COVID-19 pandemic.

The researchers showed pairs of hypothetical vaccines that varied in specific features, including effectiveness, country of origin, and cost to more than 5,000 people in France, Germany, and Sweden. Participants were asked to rate how likely they would be to choose to receive each vaccine, then selected their preferred vaccine from each pair. At the same time, the survey sought answers to questions about risk tolerance and attitudes towards vaccines.

Effectiveness and prevalence of side effects were found in statistical analysis of the results to have the greatest influence on hypothetical vaccine preference. Participants also were:

• Less likely to favor vaccines from China or Russia

• More likely to favor mRNA vaccines

• More likely to choose those that cost less.

The responses were different, however, from participants who displayed greater vaccine hesitancy. Researchers said those respondents made fewer distinctions between different attributes in their vaccine preferences.

They suggested individual difference be taken into consideration when considering vaccine preferences. Researchers added that public health messaging should clarify the attributes of different vaccines, while understanding that those efforts are not likely to be effective among the most vaccine-hesitant. Instead, they advised, messages for those demonstrating hesitancy could focus on changing attitudes towards vaccines.

"Consistent with other studies, we show that people much preferred to receive vaccines that were shown to offer a robust level of protection against COVID-19, with minimal side effects, while other differences between vaccines had minimal impact on uptake," the researchers concluded. "However, we show that these factors mattered much more for people who were already open to vaccinations in general, whereas vaccine-hesitant individuals were much less likely to accept a COVID vaccine, regardless of how effective and safe it was."

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