Background: This study aimed to calculate the seroconversion rate of the CoronaVac vaccine in healthcare workers (HCWs) 40 days after administration. Methods: Serum samples from 133 HCWs from Southern Brazil were collected one day before (Day 0) and 10, 20, and 40 days after administering the vaccines first dose. Immunoglobulin G (IgG) was quantified using immunoassays for anti-N-protein antibodies (Abbott, Sligo, Ireland) and for anti-S1 (spike) protein antibodies (Euroimmun, Lubeck, Germany). Results: Seroconversion by D 40 (20 days after the second dose) occurred in 129 (97%) HCWs for the S1 protein, and in 69 (51.87%) HCWs for the N protein. An absence of IgG antibodies (by both methodologies), occurred in two (1.5%) HCWs undergoing semiannual rituximab administration, and also in another two (1.5%) HCWs with no apparent reason. Conclusion: This study showed that CoronaVac has a high seroconversion rate when evaluated in an HCW population.