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Background: COVID-19 is a viral disease caused by the SARS-CoV-2 , leading to several variants. This study aimed to examine the effectiveness of booster doses against the Delta and Omicron variants over different follow-up times. Study Design: This was a longitudinal meta-analysis., Methods: Searches were performed in PubMed, Cochrane Library, Scopus, and Web of Science databases, and eighty studies were selected for investigation. The analyses were separately performed on the unvaccinated control group (UNVCG) and the complete two doses of the vaccine control group (C2DCG) against Delta and Omicron variants. Three outcomes were examined, including symptomatic infection, hospitalization, and death., Results: Vaccine effectiveness (VE) in UNVCG studies for symptomatic infection revealed a non-linear trend against Omicron with a peak of 67.3%, declining to 27.1% after 25 weeks after a booster dose. The mean of VE for hospitalization over time started to decrease after four weeks against Omicron and after eight weeks against Delta. The VE reached a peak at week eight (96.0%) and started to decline with a VE of 93.3% after 20 weeks after the booster dose against Delta. It was 90.8% at week four and decreased to 73.4% after 25 weeks after the booster dose against Omicron. VE in the C2DCG studies demonstrated more decreases in outcomes over time., Conclusion: Our findings showed a tendency to decrease effectiveness over time based on outcomes and variants. The early protection levels were lower in Omicron. Moreover, the VE decrease over time was stronger in Omicron compared to the Delta variant., (© 2024 The Author(s); Published by Hamadan University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.)

Background: Investigating the prevalence of the coronavirus disease 2019 (COVID-19) infection in asymptomatic children who have been in close contact with symptomatic individuals is instrumental for refining public health approaches, protecting vulnerable populations, and mitigating the broader impact of the pandemic. Accordingly, this study aimed to evaluate the incidence of COVID-19 infection in asymptomatic children who had been in close contact with parents exhibiting COVID-19 symptoms. Study Design: A cross-sectional study., Methods: The present cross-sectional study was conducted on 175 asymptomatic children who had been in close contact with COVID-19 confirmed cases in Hamadan County from March 2021 to August 2021. Reverse transcription polymerase chain reaction (RT-PCR) testing was performed on all asymptomatic children who had been in close contact with an individual with COVID-19. Furthermore, multiple logistic regressions were conducted to determine the predictors of COVID-19 transmission from family members to children., Results: Out of the 175 children in close contact with index cases, 53 (30.29%) tested positive for COVID-19 through PCR. Regarding factors related to the index case, male cases (Adjusted odds ratio [AOR]=2.29; 95% confidence interval [CI]: 1.03-5.09, P =0.041), rural dwellers (AOR=3.22; 95% CI: 1.02-10.16, P =0.046), illiterate cases (AOR=8.45; 95% CI: 1.76-40.65, P =0.008), and cases presenting with nasal congestion symptoms (AOR=9.12; 95% CI: 2.22-37.40, P =0.002) were more prone to transmitting the virus to children who had close contact with them., Conclusion: The findings of the present study suggested that asymptomatic COVID-19 infection in household contacts is significant in children who were in close contact with a COVID-19-positive patient. Therefore, it is crucial to continue to monitor this group closely., (© 2024 The Author(s); Published by Hamadan University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.)

Introduction: This study assessed the incidence and severity of side effects associated with coronavirus disease 2019 (COVID-19) vaccination among healthcare workers registered with the Medical Council of the Islamic Republic of Iran., Methodology: A retrospective cohort study was conducted on the healthcare workers focusing on the side-effects of COVID-19 vaccines from March to June 2021. Data were collected using online questionnaires. Multivariable logistic regression was used to assess the association between side effects of the vaccines and demographic variables, comorbidities, vaccine type, and history of COVID-19., Results: Out of 42,018 people who were included, 55.85% reported at least one side effect after receiving the first vaccine dose. 4.59% of those with side effects sought diagnostic intervention or were referred to treatment centers. Multivariable logistic regression indicated that being a woman, higher education, having a history of COVID-19 infection, and having comorbidities increased the risk of side effects. The AstraZeneca vaccine significantly increased the risk of side effects compared to the Sputnik vaccine, while the Sinopharm vaccine decreased this risk. The risk of developing a side effect decreased with age. The risk of moderate and severe side effects was significantly associated with gender, younger age, comorbidities, and a history of COVID-19 infection. Moderate and severe side effects were less reported by those who received the Sinopharm vaccine., Conclusions: Clinical complications after COVID-19 vaccination, directly or indirectly caused by the vaccines, are common. However, the benefits of COVID-19 vaccines greatly outweigh the risk of reversible side effects, especially among the high-risk population., Competing Interests: No Conflict of Interest is declared, (Copyright (c) 2024 Hassan Roudgari, Koorosh Etemad, Manoochehr Karami, Farideh Mostafavi, Sahar Sotoodeh Ghorbani, Kosar Farhadi Babadi, Elham Rahimi, Niloufar Taherpour, Seyed Mahmood Fattahi Masoom, Masoud Habibi, Hossein Kermanpour, Reza Laripour, Omid Manoochehri, Mohammad Raeeszadeh, Alireza Salimi, Babak Shekarchi, Ali Tajernia, Mohammad Reza Zafarghandi, Alireza Zali, Afshin Zarghi, Seyed Saeed Hashemi Nazari.)

Public health surveillance serves a crucial function within health systems, enabling the monitoring, early detection, and warning of infectious diseases. Recently, outbreak detection algorithms have gained significant importance across various surveillance systems, particularly in light of the COVID-19 pandemic. These algorithms are approached from both theoretical and practical perspectives. The theoretical aspect entails the development and introduction of novel statistical methods that capture the interest of statisticians. In contrast, the practical aspect involves designing outbreak detection systems and employing diverse methodologies for monitoring syndromes, thus drawing the attention of epidemiologists and health managers. Over the past three decades, considerable efforts have been made in the field of surveillance, resulting in valuable publications that introduce new statistical methods and compare their performance. The generalized linear model (GLM) family has undergone various advancements in comparison to other statistical methods and models. This study aims to present and describe GLM-based methods, providing a coherent comparison between them. Initially, a historical overview of outbreak detection algorithms based on the GLM family is provided, highlighting commonly used methods. Furthermore, real data from Measles and COVID-19 are utilized to demonstrate examples of these methods. This study will be useful for researchers in both theoretical and practical aspects of outbreak detection methods, enabling them to familiarize themselves with the key techniques within the GLM family and facilitate comparisons, particularly for those with limited mathematical expertise., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Background/purpose: Optimizing vaccine efficacy is of particular concern in patients undergoing hematopoietic stem cell transplantation (HSCT), which mainly have an inadequate immune response to primary SARS-CoV-2 vaccination. This investigation aimed to explore the potential prime-boost COVID-19 vaccination strategies following autologous (auto-) HSCT., Methods: In a randomized clinical trial, patients who had already received two primary doses of receptor-binding domain (RBD) tetanus toxoid (TT) conjugated SARS-CoV-2 vaccine during three to nine months after auto-HSCT were randomized to receive either a homologous RBD-TT conjugated or heterologous inactivated booster dose four weeks after the primary vaccination course. The primary outcome was comparing the anti-S IgG Immune status ratio (ISR) four weeks after the heterologous versus homologous booster dose. The assessment of safety and reactogenicity adverse events was considered as the secondary outcome., Results: Sixty-one auto-HSCT recipients were recruited and randomly assigned to receive either homologous or heterologous booster doses four weeks after the primary vaccination course. The mean ISR was 3.40 (95% CI: 2.63- 4.16) before the booster dose with a 90.0% seropositive rate. The ISR raised to 5.12 (95% CI: 4.15- 6.08) with a 100% seropositive rate after heterologous (P= 0.0064) and to 3.42 (95% CI: 2.67- 4.17) with a 93.0% seropositivity after the homologous booster doses (P= 0.96). In addition, the heterologous group suffered more AEs following the booster dosage than the homologous group, but this difference was not statistically significant (p = 0.955). In multivariable analysis, the prime-boost vaccination strategy (heterologous versus homologous), the level of ISR before the booster dose, and the length of time between auto-HSCT and booster dose were the positive predictors of serologic response to a booster dose. No serious adverse event is attributed to booster vaccination., Conclusion: In patients who were primed with two SARS-CoV-2 vaccine doses during the first year after auto-HSCT, heterologous prime-boost COVID-19 vaccination with inactivated platform resulted in considerably enhanced serologic response and non-significantly higher reactogenicity adverse events than homologous RBD-TT conjugated prime-boost COVID-19 vaccination strategy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Sharifi Aliabadi, Karami, Barkhordar, Hashemi Nazari, Kavousi, Ahmadvand and Vaezi.)

Background: The predictors of mortality among patients presenting with severe to critical disease in Nigeria are presently unknown., Aim: The aim of this study was to identify the predictors of mortality among patients with COVID-19 presenting for admission in a tertiary referral hospital in Lagos, Nigeria., Patients and Methods: The study was a retrospective study. Patients' sociodemographics, clinical characteristics, comorbidities, complications, treatment outcomes, and hospital duration were documented. Pearson's Chi-square, Fischer's Exact test, or Student's t-test were used to assess the relationship between the variables and mortality. To compare the survival experience across medical comorbidities, Kaplan Meir plots and life tables were used. Univariable and multivariable Cox-proportional hazard analyses were conducted., Results: A total of 734 patients were recruited. Participants' age ranged from five months to 92 years, with a mean ± SD of 47.4 ± 17.2 years, and a male preponderance (58.5% vs. 41.5%). The mortality rate was 9.07 per thousand person-days. About 73.9% (n = 51/69) of the deceased had one or more co-morbidities, compared to 41.6% (252/606) of those discharged. Patients who were older than 50 years, with diabetes mellitus, hypertension, chronic renal illness, and cancer had a statistically significant relationship with mortality., Conclusion: These findings call for a more comprehensive approach to the control of non-communicable diseases, the allocation of sufficient resources for ICU care during outbreaks, an improvement in the quality of health care available to Nigerians, and further research into the relationship between obesity and COVID-19 in Nigerians., Competing Interests: None

Objectives: The present study was conducted to estimate the effectiveness of (BBIBP)-CorV (Sinopharm), ChAdOx1-S/nCoV-19 (AZD1222, Oxford-AstraZeneca), rAd26-rAd5 (Gam-COVID-Vac, Sputnik V), and BIV1-CovIran (COVIran Barekat) and BBV152 COVAXIN (Bharat Biotech) vaccines against hospitalization and death of COVID-19 in Guilan Province of Iran from May 22 to December 21, 2021., Methods: This test-negative case-control study was conducted on the population aged 5 years and above by extracting information from local databases (The Medical Care Monitoring Center and The Integrated Health System). A logistic regression analysis was performed to estimate the effectiveness of the vaccines against COVID-19 hospitalization and death., Results: The total study population was 42,084, including 19,500 cases (with a positive Reverse Transcriptase-Polymerase Chain Reaction test admitted to hospitals in Guilan Province) and 22,586 controls (with a negative Reverse Transcriptase-Polymerase Chain Reaction test). Among the admitted patients, 1887 deaths occurred. The maximum effectiveness of BBIBP-CorV (Sinopharm) in preventing temporary hospitalization and regular hospitalization was observed 151 days after receiving the second dose, 95% (95% CI: 67-99.4%) and 85% (95% CI: 77-91%) respectively. The maximum effectiveness of the BBIBP-CorV (Sinopharm) vaccine 91-120 days after receiving the second dose against death was showed 56% (95% CI: 33-71%). The maximum effectiveness of ChAdOx1-S/nCoV-19 (AZD1222, Oxford-AstraZeneca) and BIV1-CovIran (COVIran Barekat) in preventing regular hospitalization and death was observed 121-150 and 61-90 days (respectively) after receiving the second dose, reaching 98% (95% CI: 94-99%) and 92% (95% CI: 48-99%), respectively for ChAdOx1-S/nCoV-19 and 95% (95% CI: 91-97%) and 89% (95% CI: 55-98%) respectively, for BIV1-CovIran., Conclusion: For almost all vaccines, the study observed an increase in effectiveness against hospitalization and death over time., (Copyright © 2022. Published by Elsevier Ltd.)

This systematic review and meta-analysis aimed to estimate the pooled prevalence of (intimate partner violence) IPV against pregnant women in the COVID-19 pandemic. A literature search was conducted in PubMed, Web of Science, and Scopus for observational studies regarding the prevalence of IPV against pregnant women during the COVID-19 pandemic. The search was performed with the following keywords: intimate partner violence, domestic violence, battered women, wife assault, partner assault, wife abuse, partner abuse, femicide, domestic homicide, pregnancy, gestation, pregnant women, COVID-19, SARS-CoV-2, 2019-nCoV, Coronavirus Disease-19, 2019 Novel Coronavirus, Wuhan Coronavirus, SARS Coronavirus 2, Wuhan Seafood Market Pneumonia Virus. Heterogeneity between the studies was assessed using Cochran's Q test and I 2 index. In addition, a random-effects model was used to estimate the prevalence of IPV. Data analysis was performed in Stata software version 16. Six articles met our inclusion criteria, which were conducted on 2213 pregnant women. The pooled prevalence of total IPV was estimated at 22 percent (95 percent Confidence Interval [CI]: 4-40 percent). Moreover, the pooled prevalence of psychological, physical, and sexual violence was reported to be 24 percent (95 percent CI: 13-35 percent), 14 percent (95 percent CI: 7-20 percent), and 6 percent (95 percent CI: 4-9 percent), respectively. Publication bias was significant ( P  = .01). According to the results, IPV against pregnant women has been relatively prevalent during the COVID-19 pandemic. Therefore, identifying the women who are at the risk of IPV is essential to preventing the consequences of maternal-fetal abuse and designing strategies to facilitate the reporting of violence during pandemics.

Background: The first large serosurvey in Iran found a SARS-CoV-2 antibody seroprevalence of 17.1% among the general population in the first wave of the epidemic by April, 2020. The purpose of the current study was to assess the seroprevalence of COVID-19 infection among Iranian general population after the third wave of the disease., Methods: This population-based cross-sectional study was conducted on 7411 individuals aged ≥10 years old in 16 cities across 15 provinces in Iran between January and March, 2021. We randomly sampled individuals registered in the Iranian electronic health record system based on their national identification numbers and invited them by telephone to a healthcare center for data collection. Presence of SARS-CoV-2-specific IgG and IgM antibodies was assessed using the SARS-CoV-2 ELISA kits. The participants were also asked about their recent COVID-19-related symptoms, including cough, fever, chills, sore throat, headache, dyspnea, diarrhea, anosmia, conjunctivitis, weakness, myalgia, arthralgia, altered level of consciousness, and chest pain. The seroprevalence was estimated after adjustment for population weighting and test performance., Results: The overall population-weighted seroprevalence adjusted for test performance was 34.2% (95% CI 31.0-37.3), with an estimated 7,667,874 (95% CI 6,950,412-8,362,915) infected individuals from the 16 cities. The seroprevalence varied between the cities, from the highest estimate in Tabriz (39.2% [95% CI 33.0-45.5]) to the lowest estimate in Kerman (16.0% [95% CI 10.7-21.4]). In the 16 cities studied, 50.9% of the seropositive individuals did not report a history of symptoms suggestive of COVID-19, implying an estimation of 3,902,948 (95% CI 3,537,760-4,256,724) asymptomatic infected individuals., Conclusions: Nearly one in three individuals were exposed to SARS-CoV-2 in the studied cities by March 2021. The seroprevalence increased about two-fold between April, 2020, and March, 2021., (© 2022. The Author(s).)

The use of reverse transcription-polymerase chain reaction (RT-PCR) is the gold standard laboratory test for diagnosing SARS-CoV-2 infection. However, it has the disadvantage of a long turnaround time and cost. The Nigeria Centre for Disease Control (NCDC) formulated a case definition for COVID-19. We sought to determine the utility of a 14-item, point-weighted clinical screening questionnaire adapted from the NCDC case definition in identifying patients more likely to have the disease. This was to aid prompt clinical decision-making., Methods: We retrospectively reviewed the data of 113 non-surgical patients presenting to the Accident and Emergency Department (A and E) of Lagos University Teaching Hospital, Lagos, Nigeria. Patients were stratified based on screening scores into low (0-2), moderate (3-5) and high (6) pre-test categories. Patients with low and high scores ≥6 were admitted to the A and E and the COVID-19 holding ward, respectively, while the moderate group had chest computed tomography scans to aid further decision-making, pending the outcome of their RT-PCR results. The validity of the triage score as compared to the RT-PCR test result was calculated and the kappa score of agreement was utilised to evaluate the concordance between two triage scores. The optimum cut-off score was also obtained based on the maximal Younden's index., Results: The frequencies of low, moderate and high pre-test scores were 34 (30%), 43 (38.1%) and 36 (31.9%), respectively. Overall, 38.1% (43/113) were RT-PCR positive. RT-PCR was positive in 26.5% (9/34) with low screening scores, 55.8% (24/43) with moderate scores and 27.8% (10/36) with high scores. The sensitivity and specificity of a high score of 6 were 25% and 92.86%, while the lower score of 3 had sensitivity and specificity of 62.5% and 58.6%, respectively., Conclusion: The screening tool showed a high specificity in its initial design, which suggests that anyone with a low score using this tool has a high probability of testing negative. We recommend a cut-off score of 4 (score A) or 6 (score B) of the current screening tool be used to increase the chances of identifying persons with COVID-19 for RT-PCR testing., Competing Interests: None

Background: Cutaneous manifestations of COVID-19 have been documented from Europe, USA, and China but none from Africa to date. Skin findings among Africans differ from Caucasians and it is important to report these in Nigerians with COVID-19., Methods: A prospective observational review involving patients seen at the Emergency triage, and Isolation wards of the Lagos University Teaching Hospital. Demographic and clinical data were captured; skin and appendages were examined by a dermatologist between 0800hrs and 1600hours to minimise visual errors of artificial light masking cutaneous lesions., Results: Of 235 participants, 17 (7.23%) had recent onset skin rash, with 7 (41.2%) experienced itching and 11 confirmed with COVID-19. There was a male: female ratio of 97:43 (2.3:1) among COVID-19 patients. Cutaneous findings were seen in 12 (5.1%) participants, with the face and trunk mostly affected and acne plus papular eruptions predominating. There was no significant relationship between COVID-19 and recent onset skin rash (χ2, p = 0.87). Only 2 of the 17 participants had a previously existing dermatoses ((χ2, p = 0.84). There was no significant relation between use of medications and onset of rashes (χ2, p = 0.72) or between those with co-morbidities and onset of rashes (χ2, p = 0.51)., Conclusion: Cutaneous manifestations were found among Nigerian patients with SARS-CoV-2 infection. Most presented with pruritus and papular eruptions and no morphologic pattern was demonstrated. Physicians and dermatologists need to be aware and look out for skin changes in SARS-CoV-2 infection as they may be early pointers to COVID-19. Keywords: Cutaneous findings, manifestations, Skin, COVID-19, Nigeria., Competing Interests: The Authors declare that no competing interest exists, (Copyright © 2021 by West African Journal of Medicine.)

Background: Clinical manifestations of COVID-19 are different. There are some risk factors for COVID-19. This study aimed to describe the epidemiological features, symptoms and mortality of the patients with COVID-19 in Iran., Methods: This were a cohort study performed on 103,179 patients with COVID-19. The demographic and clinical data were collected in selected provinces. The required data of all patients was extracted from the COVID registry system and analyzed using STATA version 14 and Excel 2016., Results: The mean age was 52.40 years for men and 52.41 years for women. About 55.2% of the study population were male and 44.8% were female. Totally, 60.9% (5085) of deaths happened in men and 39.1% (3263) in women. The mean time from onset of symptoms to hospitalization in men and women were 3.47 and 3.48 days, respectively. The mean time from onset of symptoms to isolation was 2.81 days in men and was 2.87 days in women, from onset of symptoms to death was 9.29 and 9.54 days, respectively, from onset of symptoms to discharge was 7.47 and 7.39 days, and from hospitalization to death was 6.76 and 7.05 days. Cough and shortness of breath were the most common symptoms in the patients., Conclusion: According to the results, the overall mortality rate was higher in men than women. Women with cardiovascular disease and diabetes were more likely to die. The mean time from onset of symptoms to hospitalization, isolation, and discharge was similar in men and women., (© 2021 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.)

Background: This study aimed to determine the secondary attack rate (SAR) and its determinants to describe the clinical features and epidemiological aspects of patients and determine the risk factors of COVID-19 among household contacts in Hamadan Province, west of Iran., Study Design: A cohort study., Methods: In this cohort study, a total of 323 index cases and 989 related close contacts ages more than 15 years old (family members, relatives, and co-workers) were enrolled using a manual contact tracing approach, and all participants were tested by reverse transcription polymerase chain reaction test. In this research, the frequency of symptoms was assessed, the SAR among contacts of index cases was calculated, and the risk factors of COVID-19 were evaluated by the logistic regression model., Results: The secondary attack rate for total household members of index cases was estimated at 31.7% (95% CI: 28.8-34.7). It was found that among household contacts, the highest SARs were related to spouses 47.1% (95% CI: 38.7-55.7) and grandparents/parents 39.3% (95% CI: 29.4, 49.9) of index cases, who had also higher risks to become secondary cases (adjusted odds ratio [OR]=2.98, 95% CI: 1.31-6.75 and adjusted OR=2.76, 95% CI: 1.18-6.44, respectively). Considering the occupation of contacts, unemployed and retired people and housewives were most susceptible for transmission of COVID-19. It was revealed that cough was the most prevalent symptom among index and secondary cases., Conclusion: Our findings indicated that spouses and grandparents/parents of index cases were the most susceptible individuals for COVID-19 transmission. Prolonged exposure with index case before COVID-19 diagnosis raised the chance of infection among secondary cases.

Background: Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a newly identified coronavirus. Our knowledge about the survival rate and prognostic factors of the disease is not established well. Therefore, this study aimed to identify the risk factors associated with the survival of COVID-19 cases in Hamadan province, West of Iran., Study Design: A retrospective cohort study METHODS: This retrospective cohort study was performed in Hamadan province, West of Iran. The study included patients that referred to the provincial hospitals from February 20 to September 20, 2020. The follow-up of each subject was calculated from the date of onset of respiratory symptoms to the date of death. Demographic and clinical characteristics were extracted from patients' medical records. Kaplan-Meier method, Flemington-Harrington test, and Cox regression were used for data analysis., Results: The overall 1, 5, 10, 20, 30 and 49-day survival rates were estimated at 99.57%, 95.61%, 91.15%, 87.34%, 86.91%, and 86.74%, respectively. Furthermore, survival time showed a significant association with age, gender, history of traveling to contaminated areas, co-morbidity, neoplasms, chronic diseases, and hospital units., Conclusion: In conclusion, elderly people, male gender, and comorbidities presented a greater risk of death. Therefore, it is important to pay more attention to this group of people to reduce the incidence and consequences after infection.

Background: Rapid increases in cases of COVID-19 were observed in multiple cities in Iran towards the start of the pandemic. However, the true infection rate remains unknown. We aimed to assess the seroprevalence of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 18 cities of Iran as an indicator of the infection rate., Methods: In this population-based cross-sectional study, we randomly selected and invited study participants from the general population (from lists of people registered with the Iranian electronic health record system or health-care centres) and a high-risk population of individuals likely to have close social contact with SARS-CoV-2-infected individuals through their occupation (from employee lists provided by relevant agencies or companies, such as supermarket chains) across 18 cities in 17 Iranian provinces. Participants were asked questions on their demographic characteristics, medical history, recent COVID-19-related symptoms, and COVID-19-related exposures. Iran Food and Drug Administration-approved Pishtaz Teb SARS-CoV-2 ELISA kits were used to detect SARS-CoV-2-specific IgG and IgM antibodies in blood samples from participants. Seroprevalence was estimated on the basis of ELISA test results and adjusted for population weighting (by age, sex, and city population size) and test performance (according to our independent validation of sensitivity and specificity)., Findings: From 9181 individuals who were initially contacted between April 17 and June 2, 2020, 243 individuals refused to provide blood samples and 36 did not provide demographic information and were excluded from the analysis. Among the 8902 individuals included in the analysis, 5372 had occupations with a high risk of exposure to SARS-CoV-2 and 3530 were recruited from the general population. The overall population weight-adjusted and test performance-adjusted prevalence of antibody seropositivity in the general population was 17·1% (95% CI 14·6-19·5), implying that 4 265 542 (95% CI 3 659 043-4 887 078) individuals from the 18 cities included were infected by the end of April, 2020. The adjusted seroprevalence of SARS-CoV-2-specific antibodies varied greatly by city, with the highest estimates found in Rasht (72·6% [53·9-92·8]) and Qom (58·5% [37·2-83·9]). The overall population weight-adjusted and test performance-adjusted seroprevalence in the high-risk population was 20·0% (18·5-21·7) and showed little variation between the occupations included., Interpretations: Seroprevalence is likely to be much higher than the reported prevalence of COVID-19 based on confirmed COVID-19 cases in Iran. Despite high seroprevalence in a few cities, a large proportion of the population is still uninfected. The potential shortcomings of current public health policies should therefore be identified to prevent future epidemic waves in Iran., Funding: Iranian Ministry of Health and Medical Education., Translation: For the Farsi translation of the abstract see Supplementary Materials section., (Copyright © 2021 Elsevier Ltd. All rights reserved.)