inclusion criteria: age 18-65 years old human resources in persahabatan central general hospital while being a research subject wear ppe according to their respective work standards. not previously infected with covid-19, or have been infected with covid-19 19 previously with non-reactive igg serological results. have not received a covid-19 vaccine or have received 2nd dose of vaccine covid-19 but manifest non-reactive igg serological results subject voluntarily gave written consent to participate in this research.

inclusion criteria: age 18-65 years old human resources in persahabatan central general hospital while being a research subject wear ppe according to their respective work standards. not previously infected with covid-19, or have been infected with covid-19 19 previously with non-reactive igg serological results. have not received a covid-19 vaccine or have received 2nd dose of vaccine covid-19 but manifest non-reactive igg serological results subject voluntarily gave written consent to participate in this research.