Residual humoral immunity sustained over decades in a cohort of vaccinia-vaccinated individuals.

In 2019, Singapore experienced a case of imported Monkeypox. As with smallpox, disease can be prevented through vaccination, which was mandatory for Singaporean infants until 1981. However, the degree of residual immunity in older vaccinated Singaporeans remains unknown. Sera from individuals born from 1946-1984 were therefore tested and those born prior to 1981 were found to have higher anti-vaccinia IgG and neutralizing activity titres. This suggests that protective humoral immunity remains which could reduce disease severity in an orthopoxvirus outbreak. Correlation between IgG and neutralizing titres was observed indicating that serology could be used as a surrogate marker for immunity.