Sequential Enhanced Safety Study of a Novel Coronavirus Messenger RNA (mRNA) Vaccine in Adults Aged 18 Years and Older.

According to the results of the preliminary phase I clinical trial, the incidence of adverse reactions in subjects in the 0.3 ml dose group was lower than in the 0.5 ml dose group and the degree of adverse reactions was weaker. The dose of 0.3ml was chosen for the current study. The trial was designed to enroll 800 adult subjects aged 18 years and older who had completed three doses of inactivated New Coronavirus vaccine with an interval of more than 6 months between doses, and the proportion of elderly people aged 60 years and older was approximately 20%. Subjects will receive 0.3 ml of mRNA vaccine, complete a 1-dose immunization program, and undergo safety observations.