key: cord-0728783-bt6zgr36 authors: Toniassoa, Sheila de Castro Cardoso; Fernandesa, Fernando Schmidt; Jovelevithsb, Dvora; Filhoc, Fábio Fernandes Dantas; Takahasid, Anderson Yudi; Baldina, Camila Pereira; Pereiraa, Robson Martins; da Silvae, Luciana Pereira; Bruma, Maria Carlota Borba title: Reduction in COVID-19 prevalence in health care workers in a university hospital in southern Brazil after the start of vaccination. date: 2021-07-14 journal: Int J Infect Dis DOI: 10.1016/j.ijid.2021.07.025 sha: d297e48e2ad6f593d5c408e8f53a38830a1daf04 doc_id: 728783 cord_uid: bt6zgr36 Introduction: The quick spread of SARS-CoV-2 led to the development of vaccines that are capable of reducing infection and the number of more severe COVID-19 cases. Aim: To assess COVID-19 prevalence among health care workers (HCWs) after vaccination against SARS-CoV-2. Methods: Cross-sectional study on the prevalence of COVID-19 diagnosis among 7.523 HCWs vaccinated against SARS-CoV-2 with Coronavac and ChAdOx1 nCoV-19 in a university hospital, in southern Brazil, between January 18, 2021 and March 18, 2021.The variables evaluated were: sex, age, work area, role, source of infection, previous diagnosis of COVID-19, date of vaccine administration, type of vaccine, and need for hospitalization. The statistical analysis used Poisson regression and Fisher's Exact Test with the SPSS software version 25 and level of significance set at 5%. Results: 813 vaccinated HCWs showed symptoms suggestive of COVID-19, and 35.4% (288) who underwent RT-PCR for SARS-CoV-2 had a detectable result. There was a reduction of 62% in new cases of COVID-19 among HCWs in the institution after seven weeks of the start of the vaccine rollout. Conclusion: Our data suggest that the vaccines used by the institution reduced the number of COVID-19 cases among health care workers, showing the effectiveness of the vaccines. There is evidence that vaccines are able to reduce infection and the number of more severe cases of COVID-19 (Bradley T,et al.,2021; Keehner J, et al.,2021; Daniel W, et al,2021; Benenson S, et al.; . The P1 variant of SARS-CoV-2 is refractory to multiple neutralizing monoclonal antibodies (Wang P, et al., 2021) . This may lead to antigen alterations that impair vaccine protection, leading to a diagnosis of infection in individuals in whom vaccine efficacy was evidenced (Wang P, et al.,2021) . A cross-sectional study on the prevalence of COVID-19 diagnosis was conducted among 7.523 health care workers (HCWs) vaccinated against SARS-CoV-2 with Coronavac, inactivated virus vaccine, and ChAdOx1 nCoV-19, using chimpanzee adenovirus as a viral vector for the expression of the SARS-CoV-2 Spike protein, in a university hospital in southern Brazil. 4.260 HCWs received Coronavac (3.676 with two doses and 584 with only one dose) and 3.263 received one dose of ChAdOx1 nCoV-19 between January 18, 2021 and March 18, 2021.It was found that 813 health professionals with symptoms suggestive of COVID-19 performed an RT-PCR (reverse transcriptase reaction followed by a polymerase chain reaction) test for SARS -CoV-2 and received at least one dose of the SARS-CoV-2 vaccine in the first nine weeks of vaccination. The variables evaluated were: sex, age, work area, role, source of infection, previous diagnosis of COVID-19, date of vaccine administration, type of vaccine (ChAdOx1 nCoV-19 and Coronavac), date and result of the RT-PCR assay for SARS-CoV-2, number of professionals diagnosed with COVID-19 after vaccination, need for hospitalization and in the Intensive Care Unit (ICU). Prevalence Ratio (PR) measure with 95% CI, estimated by the Poisson Regression analysis with robust variance adjustment, was used to verify the factors and the strength of the association with the PCR test result in the general sample and stratified by type of vaccine, and Fisher's exact test was used for the association of the vaccine with the hospitalization and ICU outcomes among COVID-19 patients. Analyses were performed using the SPSS software version 25, and the level of significance was set at 5%. The 20-40 and 41-60 age groups were represented similarly in our sample, that is, 48% and 48.6%, respectively, of the total of HCWs evaluated. 81.7% of the 813 HCWs evaluated were females, and 35.4% (288) of those who underwent RT-PCR for SARS-CoV-2 showed a detectable result. (Table 1 ). The diagnosis of COVID-19 in the past reduced the prevalence of new infections by 68% (PR: 0.32 95% CI: 0.19 -0.56). A similar result was observed with the ChAdOx1 nCoV-19 vaccine, with a decrease in infection prevalence of 22% (PR: 0.78 95% CI: 0.64 -0.96). After the first dose, infection prevalence decreased by 7% every week (PR: 0.93 95% CI: 0.89 -0.97) regardless of the type of vaccine. Among the 314 suspected cases who had received the ChAdOx1 nCoV-19 vaccine, a positive diagnosis for COVID-19 was observed in 30.3%. An important finding was that a previous diagnosis of COVID-19 over 45 days ago reduced prevalence by 71% (PR: 0.29 95% CI: 0.11 -0.75) among those professionals. When only professionals who received one dose of ChAdOx1 nCoV-19 were considered, prevalence was reduced by 10% each week after vaccination (PR: 0.90 95% CI: 0.84 -0.96) ( Table 2) . Among the 399 suspected cases who had received the Coronavac vaccine, a positive diagnosis for COVID-19 was observed in 38.7%. Physicians showed a 2.25-fold increased prevalence compared to other health professionals with higher education for a positive diagnosis of COVID-19 (PR: 2.25 95% CI: 1.08 -4.69). A previous diagnosis of COVID-19 reduced prevalence by 65% (PR: 0.35 95% CI: 0.18 -0.67) ( Table 2 ). The hospitalization outcome was observed in 14 of 288 COVID-19 patients. However, no cases with positive RT-PCR died after the administration of both vaccines during the period under study. Our data suggest that, after the first dose, the prevalence of infection decreased every week, regardless of the type of vaccine. ChAdOx1 nCoV-19 seems to provide, within our population, a better protective factor in relation to COVID-19, and further studies are needed to identify the cause of this difference. The higher prevalence among physicians, identified in our population, may be associated with the prevalence of double working hours, with different levels of exposure and protection against COVID- The different levels of protection against COVID-19, such as the use of personal protective equipment, may be associated with a lower prevalence of positive cases in the occupational environment when compared to other environments. However, more studies are needed. The presence of a previous diagnosis of COVID-19 was a protective factor against new SARS-CoV-2 infections. In agreement with our data, a Danish study and a study conducted in Qatar pointed out that the presence of a previous diagnosis of COVID-19 infection can provide up to 78.8% and 95 % of protection against a new infection (Hansen CH, et al.,2021; Abu-Raddad LJ, et al.,2021) . Our data, as well as that of the study conducted in Israel evidenced a decline in cases of and in the severe forms of the disease following the start of the vaccine rollout (Rossman, H, et al.,2021) . Our data suggest that the vaccines used by the institution reduced the number of COVID-19 cases among HCWs and protected against severe forms of the disease. The researchers declare that they have no conflicts of interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. (Baptista MC, et al., 2021) . ** Non COVID care: assistance to patients without a diagnosis of COVID-19. ***COVID-19 care: assistance to patients diagnosed with COVID-19. ****Other health professionals with higher education. (0.18-0.67) *Without patient assistance: jobs that do not require contact with patients. ** Non COVID patient assistance: assistance to patients without a diagnosis of COVID-19. *** COVID patient assistance: assistance to patients diagnosed with COVID-19. ****Other health professionals with higher education. 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