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Background: Even though a few years have passed since the coronavirus disease 2019 (COVID-19) outbreak, information regarding certain aspects of the disease, such as post-infection immunity, is still quite limited. This study aimed to evaluate post-infection protection and COVID-19 features among healthcare workers (HCWs), during three successive surges, as well as the rate of severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) reinfection, reactivation, re-positivity, and severity. Methods: This cross-sectional population-level observational study was conducted from 20 April 2020 to 18 February 2021. The study population included all HCWs in public or private hospitals in Fars Province, Southern Iran. The infection rate was computed as the number of individuals with positive polymerase chain reaction (PCR) tests divided by the total number of person- days at risk. The re-infection was evaluated after 90 days. Results: A total of 30,546 PCR tests were performed among HCWs, of which 13,749 (61.94% of total HCWs) were positive. Considering the applied 90-day threshold, there were 44 (31.2%) cases of reactivation and relapse, and 97 (68.8% of infected and 1.81% of total HCWs) cases of reinfection among 141 (2.64%) diagnosed cases who experienced a second episode of COVID-19. There was no significant difference in symptoms (P=0.65) or the necessity for ICU admission (P=0.25). The estimated protection against repeated infection after a previous SARS- CoV-2 infection was 94.8% (95% CI=93.6-95.7). Conclusion: SARS-CoV-2 re-positivity, relapse, and reinfection were rare in the HCW population. After the first episode of infection, an estimated 94.8% protection against recurring infections was achieved. A preprint version of this manuscript is available at DOI: 10.21203/rs.3.rs-772662/v1 (https://www.researchsquare.com/ article/rs-772662/v1). [ABSTRACT FROM AUTHOR]

Fascioliasis is a human and veterinary concern in Iran. This cross-sectional population-based study was conducted to determine the seroprevalence of human fascioliasis among nomadic people in Kohgiluyeh and Boyer-Ahmad province located in the southwest of Iran. Venous blood samples were collected from 933 nomads in the area. A predesigned questionnaire containing basic epidemiological information was filled out for each subject during the sampling. Sera were evaluated for anti-Fasciola antibodies, using excretory-secretory (ES) antigen of Fasciola hepatica in an ELISA system. Of 933 recruited subjects, 726 (77.8%) were females and 206 (22.1%) were males. The mean age of the participants was 43.1 (±16.7) years old. Most of the subjects (24.6%) were in the age group of 21-30 years old. Anti-Fasciola antibodies were detected in 24 (2.6%) out of 933 cases. Of 24 seropositive cases, 3 (12.5%) were male and 21 (87.5%) were female. The differences between the seropositivity and sex, age, level of education and residence area were not statistically significant (p >0.05). Findings of the current study demonstrated that the seroprevalence of fascioliasis in the studied nomadic population was significant, and that preventive and control measures should be taken to prevent the disease from spreading and causing even greater health and economic problems in this area.