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Background: CoronaVac, a vaccine containing inactivated SARS-CoV-2, demonstrated efficacy of 50.39% 14 days or more after the 2nd dose. The objective of this study is to report the occurrence of symptomatic COVID-19 in a cohort of HCW vaccinated with CoronaVac and to estimate its effectiveness. Methods: CoronaVac was given to HCWs in Hospital das Clinicas on 18-21 January, 2021 (epi week 3) (22,402 HCWs), and on 14-16 February, 2021 (epi week 7) (21,652 HCWs). Weekly cases of symptomatic COVID-19 were evaluated. Using the period from 2020 epi week 24 through 2021 epi week 2 (before vaccination), a Poisson regression was fit to model the HCWs with COVID-19 of the hospital, and the officially reported cases in the city of Sao Paulo. The predicted numbers of cases among HCWs for 2021 epi weeks 3-12 were then compared to the observed numbers of cases (after vaccination). Effectiveness was estimated for weeks 9-12 (2 to 5 weeks after the 2nd dose). 142 samples after vaccination were evaluated for SARS-CoV-2 variants of concern. Results: Since the 1st dose there were 380 HCW diagnosed with COVID-19. On visual analysis, the number of cases of COVID-19 in the city increased sharply in 2021. The number of cases among the HCW did not follow. The estimated effectiveness 2 and 3 weeks after 2nd dose was 50.7% and 51.8%, respectively, and increased over the next 2 weeks. 67/142 samples (47%) were variants of concern, mostly P1 (57). Conclusion: Coronavac is effective in preventing COVID-19.

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Background: COVID-19 disease (Coronavirus disease 2019) caused by SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2) is widespread worldwide, affecting more than 11 million people globally (July 6th, 2020). Diagnostic techniques have been studied in order to contain the pandemic. Immunochromatographic (IC) assays are feasible and low cost alternative for monitoring the spread of COVID-19 in the population. Methods: Here we evaluate the sensitivity and specificity of eleven different immunochromatografic tests in 98 serum samples from confirmed cases of COVID-19 through RT-PCR and 100 negative serum samples from blood donors collected in February 2019. Considering the endemic situation of Dengue in Brazil, we also evaluated the cross-reactivity with Dengue using 20 serum samples from patients with confirmed diagnosis for Dengue collected in early 2019 through four different tests. Results: Our results demonstrated agreement between immunochromatographic assays and RT-PCR, especially after 10 days since the onset of symptoms. The evaluation of IgG and IgM antibodies combined demonstrated a strong level of agreement (0.85) of IC assays and RT-PCR. It was observed cross-reactivity between Dengue and COVID-19 using four different IC assays for COVID-19 diagnosis. The specificity of IC assays to detected COVID-19 IgM antibodies using Dengue serum samples varied from 80% to 85%; the specificity of IgG detection was 100% and total antibody was 95%. Conclusions: We found high sensitivity, specificity and good agreement of IC assays, especially after 10 days onset of symptoms. However, we detected cross-reactivity between Dengue and COVID-19 mainly with IgM antibodies demonstrating the need for better studies about diagnostic techniques for these diseases.