unseriousness
n. 不认真;不严肃;不庄重
例句
With regard to varicella vaccine, the reluctance to vaccination were due mostly to the avoidance of medical interventions and perceived unseriousness of varicella.
的民众表示愿意接种水痘疫苗,不愿接种的理由多为尽可能避免医疗行为,以及自觉水痘并非严重的疾病。