  Effective public health messaging benefits from understanding antecedents to
unstable attitudes that are more likely to be influenced. This work
investigates the relationship between moral and emotional bases for attitudes
towards COVID-19 vaccines and variance in stance. Evaluating nearly 1 million X
users over a two month period, we find that emotional language in tweets about
COVID-19 vaccines is largely associated with more variation in stance of the
posting user, except anger and surprise. The strength of COVID-19 vaccine
attitudes associated with moral values varies across foundations. Most notably,
liberty is consistently used by users with no or less variation in stance,
while fairness and sanctity are used by users with more variation. Our work has
implications for designing constructive pro-vaccine messaging and identifying
receptive audiences.
