THE CONTAGION NUMBER: HOW FAST CAN A DISEASE SPREAD?

The overall purpose of this paper is to define a new metric on the spreadability of a disease. Herein, we define a variant of the well-known graph-theoretic burning number (BN) metric that we coin the contagion number (CN). We aver that the CN is a better metric to model disease spread than the BN as the CN concentrates on first time infections. This is important because the Centers for Disease Control and Prevention report that COVID-19 reinfections are rare. This paper delineates a novel methodology to solve for the CN of any tree, in polynomial time, which addresses how fast a disease could spread (i.e., a worst-cast analysis). We then employ Monte Carlo simulation to determine the average contagion number (ACN) (i.e., a most-likely analysis) of how fast a disease would spread. The latter is analyzed on scale-free graphs, which are specifically designed to model human social networks (sociograms). We test our method on some randomly generated scale-free graphs and our findings indicate the CN to be a robust, tractable (the BN is NP-hard even for a tree), and effective disease spread metric for decision makers. The contributions herein advance disease spread understanding and reveal the importance of the underlying network structure. Understanding disease spreadability informs public policy and the associated managerial allocation decisions. © 2023 by the authors.

Incidence of SARS-CoV-2 re-infection in anti-nucleocapsid IgG-positive healthcare workers: a prospective cohort study.

BACKGROUND : Since the pandemic of SARS-CoV-2 began, our understanding of the pathogenesis and immune responses to this virus has continued to evolve. It has been shown that this infection produces natural detectable immune responses in many cases. However, the duration and durability of immunity and its effect on the severity of the illness are still under investigation. Moreover, the protective effects of antibodies against new SARS-CoV-2 variants still remain unclear. OBJECTIVES: To assess the incidence and associated demographic features of SARS-CoV-2 infection in anti-nucleocapsid IgG-positive and anti-nucleocapsid IgG-negative healthcare workers. MATERIAL AND METHODS: This prospective longitudinal cohort study was conducted in Peshawar Medical College group of hospitals of Prime Foundation. Anti-nucleocapsid IgG sero-positive and anti-nucleocapsid IgG sero-negative healthcare workers were followed for a period of 6 months (from 1 Aug 2020 to 31 Jan 2021), and the incidence of SARS-CoV-2 was confirmed by RT-PCR. RESULTS: A total number of 555 cohorts were followed for a period of 6 months; of them 365 (65.7%) were anti-nucleocapsid-negative (group A) and 190 (34.3%) were anti-nucleocapsid-positive (group B) healthcare workers. The mean age of the study cohort was 33.85 ± 9.80 (anti-N (-), 34.2 ± 10.58; anti-N ( +), 33.5 ± 9.50). The median antibody level in anti-nucleocapsid-positive HCWs was 15.95 (IQR: 5.24-53.4). Male gender was the majority in both groups (group A, 246 (67%), group B, 143 (48%)) with statistically significant difference (P < 0.05). Majority of the HCWs were blood group B in both groups (34% each). None of the 190 anti-nucleocapsid-positive HCWs developed subsequent SARS-CoV-2 re-infection, while 17% (n = 65) HCWs developed infection in anti-nucleocapsid-negative group during the 6-month follow-up period. CONCLUSION: In conclusion, none of the anti-nucleocapsid-positive HCWs developed SARS-CoV-2 re-infection in this study, and the presence of IgG anti-nucleocapsid antibodies substantially reduce the risk of re-infection for a period of 6 months.

Epitope Coverage of Anti-SARS-CoV-2 Nucleocapsid IgA and IgG Antibodies Correlates with Protection against Re-Infection by New Variants in Subsequent Waves of the COVID-19 Pandemic.

The COVID-19 pandemic continues to affect individuals across the globe, with some individuals experiencing more severe disease than others. The relatively high frequency of re-infections and breakthrough infections observed with SARS-CoV-2 highlights the importance of extending our understanding of immunity to COVID-19. Here, we aim to shed light on the importance of antibody titres and epitope utilization in protection from re-infection. Health care workers are highly exposed to SARS-CoV-2 and are therefore also more likely to become re-infected. We utilized quantitative, multi-antigen, multi-epitope SARS-CoV-2 protein microarrays to measure IgG and IgA titres against various domains of the nucleocapsid and spike proteins. Potential re-infections in a large, diverse health care worker cohort (N = 300) during the second wave of the pandemic were identified by assessing the IgG anti-N titres before and after the second wave. We assessed epitope coverage and antibody titres between the 'single infection' and 're-infection' groups. Clear differences were observed in the breadth of the anti-N response before the second wave, with the epitope coverage for both IgG (p = 0.019) and IgA (p = 0.015) being significantly increased in those who did not become re-infected compared to those who did. Additionally, the IgG anti-N (p = 0.004) and anti-S titres (p = 0.018) were significantly higher in those not re-infected. These results highlight the importance of the breadth of elicited antibody epitope coverage following natural infection in protection from re-infection and disease in the COVID-19 pandemic.

Impact of Vaccination on Symptomatology among COVID-19 Infection and Re-infection

Background: Present indications proposed strong bases that people suffered from SARS-CoV-2 infection are still susceptible to re-infection. Studies proposed that one of the COVID-19 viral vector vaccine and two genetic mRNA vaccines presented generous defense for COVID-19 infection as well as persisted effectively against mutated variants. Aim(s): To observe the impact of vaccination symptomatology among patients presented with COVID-19 infection for the first time and compared it with those of re-infected cases during 5th wave in Pakistan Methods: This descriptive study included a total of 248 patients were interviewed using a semi-structured questionnaire. Patients themselves or their attendants receiving reports from the counter of various laboratories were targeted. A verbal informed consent was taken before data collection. Following information about, job nature, side effects after vaccination, comorbidities, level of symptoms (i.e. mild, moderate and high) Results: A total 248 patients consisting of 52.0% females and 48.0% males with overall mean age of 35.96+/-17.94 years. A total of 37.5% patients were re-infected further proportion of male gender 46.2% and 29.5% were females. Proportion of re-infection in fully vaccinated group remained to be 35.5%, partially vaccinated as 43.9% and unvaccinated as 42.9%. ANOVA was applied to compare the severity of symptoms with full, partial and unvaccinated patients. Conclusion(s): Lack of discernable variations in protection against COVID-19 re-infection were observe through vaccination or prior infection. Ultimately trends show an enhancement in level of protection from re-infection was shown as prior infection alone, partial vaccination and full vaccination respectively. Copyright © 2022 Lahore Medical And Dental College. All rights reserved.

An Automated Approach for Screening COVID-19 from Thermal Images Using Convolutional Neural Network

The world has seen the disastrous effect caused by COVID-19 on humankind. The rapidity of COVID-19 transmission, re-infections, post-COVID-19 symptoms, and the emergence of new COVID-19 strands have disrupted the global healthcare systems. Consequently, screening for COVID-19 cases has become of the utmost importance. As temperature and mask checks help significantly to prevent the rapid spread of COVID-19, automating this process in public places has become indispensable. In this work, we propose an end-to-end approach for mask detection followed by temperature for efficient screening. The proposed model achieved 93.5%, 96.7%, and 97.7% precision, recall, and mAP when trained on the thermal surveillance dataset and tested on a lightning dataset consisting of images with varying intensities. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Investigating the frequency of infection with covid-19 after vaccination in medical personnel according to their epidemiological characteristics, department of service, and history of chronic diseases(A study in the west of Iran)

Background and Aim: The emergence of new SARS-CoV-2 strains all over the world has caused concerns about this infection and the effectiveness of the vaccines produced to cope with the resulting pandemic. The present study aimed to investigate the frequency of infection with covid-19 after vaccination, according to their epidemiological characteristics, department of service, and history of chronic diseases. Method(s): In the present cross-sectional study, all the vaccinated healthcare workers working in Shahid Rahimi Hospital in Khorramabad city were included in the study using a census method and were examined in terms of covid-19 infection after covid-19 vaccination. In the present study, all individuals with a positive PCR test or CT scan findings consistent with covid-19 were considered as new infections after vaccination. The required data were collected through a multi-part questionnaire, including the variables of age, gender, occupation, body mass index, chronic disease records, and PCR test results. Data were analyzed using SPSS-23 statistical software. Result(s): After vaccination, the rate of re-infection with covid-19 (according to the definitive result of the PCR test) was 13% in the study subjects. According to the results of the chi-square test, the difference in the frequency of re-infection with covid-19 after vaccination in the subjects was statistically significant based on age (pv=0.019) and gender (pv=0.007), but it was not statistically significant based on body mass index (pv=0.31). Despite the highest frequency of re-infection with covid-19 after vaccination in nurses (16.1%) compared to service workers (5%) and physicians (7.7%), this difference was not statistically significant (pv=0.619) and there was no correlation between the type of occupation of the people and re-infection with Covid-19 after vaccination in the studied people. The difference in the frequency of infection with covid-19 after vaccination in the study subjects was statistically significant based on department of service (pv= 0.019) and history of chronic diseases (pv=0.029). The frequency of re-infection with covid-19 after vaccination was 24.3% in people who had a history of chronic disease and 11.4% in people who did not have a history of chronic disease. Conclusion(s): The healthcare workers providing medical services in hospitals are among the high-risk groups for infection with covid-19 owing to their type of occupation and work environment. Copyright © 2022, Anka Publishers. All rights reserved.

A Modified SIRV Model for COVID-19

The spread of COVID-19 has caused irreparable and enormous damage to many families around the world, so using mathematical models to further study the changing pattern of the infection's population caused by the spread of the coronavirus can help people to predict the trend of its changes. In this paper, on top of the logistic growth and classical SIR epidemiological models, the author develops a new SIRV model, including the effect of reinfection and breakthrough infection, to illustrate some properties of the spread of COVID-19. This study identified several fundamental properties and basic reproduction numbers of this SIRV COVID-19 model and further searched for the steady-state or equilibrium point of the model using dimensionless methods. This study demonstrated the following: first, the author proved that the solution of the model is positive under non-negative conditions. Second, the author applied the next generation matrix method to determine the basic reproduction number of the COVID-19 virus in the model and found that the calculation of the basic reproduction number in the model is the same as in the classical SIR model. Finally, the author used the dimensionless method to obtain expressions for the equilibrium points of the model in both disease-free and diseased cases. © 2022 SPIE.

Primary SARS-CoV-2 Infections, Re-infections and Vaccine Effectiveness during the Omicron Transmission Period in Healthcare Workers of Trieste and Gorizia (Northeast Italy), 1 December 2021-31 May 2022.

Objective: To evaluate the incidence of primary and recurrent COVID-19 infections in healthcare workers (HCWs) routinely screened for SARS-CoV-2 by nasopharyngeal swabs during the Omicron wave. Design: Dynamic Cohort study of HCWs (N = 7723) of the University Health Agency Giuliano Isontina (ASUGI), covering health services of the provinces of Trieste and Gorizia (Northeast Italy). Cox proportional hazard model was employed to estimate the risk of primary as well as recurrent SARS-CoV-2 infection from 1 December 2021 through 31 May 2022, adjusting for a number of confounding factors. Results: By 1 December 2021, 46.8% HCWs of ASUGI had received the booster, 37.2% were immunized only with two doses of COVID-19 vaccines, 6.0% only with one dose and 10.0% were unvaccinated. During 1 March 2020-31 May 2022, 3571 primary against 406 SARS-CoV-2 recurrent infections were counted among HCWs of ASUGI, 59.7% (=2130/3571) versus 95.1% (=386/406) of which occurring from 1 December 2021 through 31 May 2022, respectively. All HCWs infected by SARS-CoV-2 during 1 December 2021 through 31 May 2022 presented mild flu-like disease. Compared to staff working in administrative services, the risk of primary as well as recurrent SARS-CoV-2 infection increased in HCWs with patient-facing clinical tasks (especially nurses and other categories of HCWs) and in all clinical wards but COVID-19 units and community health services. Regardless of the number of swab tests performed during the study period, primary infections were less likely in HCWs immunized with one dose of COVID-19 vaccine. By contrast, the risk of SARS-CoV-2 re-infection was significantly lower in HCWs immunized with three doses (aHR = 0.58; 95%CI: 0.41; 0.80). During the study period, vaccine effectiveness (VE = 1-aHR) of the booster dose declined to 42% against re-infections, vanishing against primary SARS-CoV-2 infections. Conclusions: Though generally mild, SARS-CoV-2 infections and re-infections surged during the Omicron transmission period. Compared to unvaccinated colleagues, the risk of primary SARS-CoV-2 infection was significantly lower in HCWs immunized just with one dose of COVID-19 vaccines. By Italian law, HCWs immunized only with one dose were either suspended or re-assigned to job tasks not entailing patient facing contact; hence, while sharing the same biological risk of unvaccinated colleagues, they arguably had a higher level of protection against COVID-19 infection. By contrast, SARS-CoV-2 re-infections were less likely in HCWs vaccinated with three doses, suggesting that hybrid humoral immunity by vaccination combined with natural infection provided a higher level of protection than vaccination only. In this stage of the pandemic, where SARS-CoV-2 is more infectious yet much less pathogenic, health protection measures in healthcare premises at higher biological risk seem the rational approach to control the transmission of the virus.

Effect of awareness, quarantine and vaccination as control strategies on COVID-19 with Co-morbidity and Re-infection.

In this paper, a deterministic compartmental model is presented to assess the impact of vaccination and non-pharmaceutical interventions (social distance, awareness, face mask, and quarantine) on the transmission dynamics of COVID-19 with co-morbidity and re-infection. An expression for the basic reproduction number is then derived for this model. Theoretical analysis shows that the model exhibits backward bifurcation phenomenon when the basic reproduction number is less than unity. But for the case of no re-infection, the model has a globally asymptotically stable disease-free equilibrium (DFE) when the basic reproduction number is less than unity. Furthermore, it is shown that in the case of no re-infection, a unique endemic equilibrium point (EEP) of the model exists which is globally asymptotically stable whenever the reproduction number is greater than unity. From the global sensitivity and uncertainty analysis, we have identified mask coverage, mask efficacy, vaccine coverage, vaccine efficacy, and contact rate as the most influential parameters influencing the spread of COVID-19. Numerical simulation results show that the use of effective vaccines with proper implementation of non-pharmaceutical interventions could lead to the elimination of COVID-19 from the community. Numerical simulations also suggest that the control strategy that ensures a continuous and effective mass vaccination program is the most cost-effective control strategy. The study also shows that in the presence of any co-morbidity and with the occurrence of re-infection, the disease burden may increase.

Antibody responses after two doses of SARS-CoV-2 mRNA-1273 vaccine in an individual with history of COVID-19 re-infection.

We present a case of a 58-year-old Japanese man with a history of 2 previous COVID-19 infections, who received 2 doses of mRNA-1273 vaccine. We are not aware of any previous study regarding antibody tendency after 2 infections and 2 vaccinations. We evaluated his IgG titer of antispike protein and neutralizing activity from the first infection before and after 2 doses of vaccine. Both antispike IgG titer and neutralizing activity showed a tendency to decline almost 1 year after initial infection; they rapidly increased after the first vaccination, and they remained high after the second vaccination. Although this is a single case report, it seems to have generalizability because the findings are consistent with previous reports regarding single infections or 3 doses of vaccination. Our findings suggest that a single booster shot may provide sufficient protection and aid the understanding of immunologic responses of vaccination in patients with COVID-19 with history of re-infection.

Epidemiology of SARS--CoV--2 with Implications of Reinfection Update After 01 Year of Ongoing Pandemic:: Cross Sectional Study From Tertiary Care Hospital From Southern Region of Pakistan

Objective: To share the epidemiological, clinical and laboratory -based evidence of severe acute respiratory syndrome Corona Virus-2 with focus on the cases of re-infection;an update after one year of the ongoing pandemic. Study Design: Prospective observational study. Place and Duration of Study: Department of Pathology, in collaboration with Department of Medicine, Combined Military Hospital, Malir, from Mar 2020 to Feb 2021. Methodology: Total 5190 nasopharyngeal swabs were collected and transported to the laboratory in viral transport media for severe acute respiratory syndrome Corona Virus-2, from all symptomatic patients with a history of exposure/traveling from endemic areas and those requiring admission in hospital and were screened for COVID-19 as per hospital standing protocols. Results: 561(10.8%) patients were PCR positive for severe acute respiratory syndrome Corona Virus-2. The mean age of patients was 39.45±31.9 years and a majority of patients were males 426 (76%). The most common symptoms were fever and dry cough followed by myalgia and shortness of breath. 37 (9%) patients died due to the severity of the illness. Total 6 (1.46%) cases of laboratory-confirmed reinfection of severe acute respiratory syndrome Corona Virus-2 were reported. 2(33%) cases of reinfection were observed in health care workers, mortality was seen in a single patient associated with old age and comorbidities. Conclusion: In our study, the severity of the disease was directly related to the age of patients and underlying comorbidities. Reinfection was associated with increased viral load and exposure to the infected environment. © 2022, Army Medical College. All rights reserved.

OMICRON (B.1.1.529): A new SARS-CoV-2 variant of concern mounting worldwide fear.

Recent emergence of the SARS-CoV-2 variant as OMICRON has become a global concern. This short note highlights the identification and global spread of OMICRON which has spread over 77 nations by now, which resulted in many hypotheses about its origin and degree of infectivity. The detection of mutations in the RBD region of Spike protein is a concern by surpassing vaccine immunity. The ahead will speak about its transmission potentiality, infectivity, disease morbidity as well as its effect on COVID-19 vaccines.

Clinical Evaluation of Conventional Human Coronavirus Infection in Adults.

Human coronaviruses (HCoVs) are distributed globally and they cause a range of respiratory symptoms. Since HCoV infection usually causes mild upper respiratory tract disease and currently has no specific therapy, there are limited reports on its features, especially in adults. We aimed to evaluate the features of HCoV infections in clinical settings. Adult patients with respiratory symptoms from October 2014 to September 2019 at Nagasaki Genbaku Isahaya Hospital were enrolled. Multiplex reverse transcription-polymerase chain reaction as performed for 15 viruses, including HCoVs, and eight bacterial species on the patients' respiratory specimens. A total of 121 cases were recruited with HKU1, OC43, 229E, and NL63 strains in 80, 21, 12, and 11 cases, respectively. The percentage of HCoV-infected patients peaked in winter (47.5%). Symptoms of fever (69.4%), cough (47.9%), and comorbidities of asthma/cough variant asthma (34.7%) were frequently observed. Lymphocytopenia and increased C-reactive protein levels were observed in laboratory tests. Co-infection with other viruses was identified in 38.8% of the cases. In the repeat-positive cases, 42% were repeat positive within 100 days. HCoV-infected patients showed winter seasonality with a high frequency of comorbidity with asthma and co-infections. Re-infection within an early period was suspected, but further consideration is required.

Immune durability and protection against SARS-CoV-2 re-infection in Syrian hamsters.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a pandemic. As immunity to endemic human coronaviruses (i.e. NL63 or OC43) wanes leading to re-infection, it was unknown if SARS-CoV-2 immunity would also decline permitting repeat infections. Recent case reports confirm previously infected individuals can become re-infected; however, re-infection may be due to heterogeneity in the initial infection or the host immune response, or may be the result of infection with a variant strain that escapes pre-existing immunity. To control these variables, we utilized the Syrian hamster model to evaluate the duration of immunity and susceptibility to re-infection with SARS-CoV-2. Hamsters were given a primary mock or SARS-CoV-2 infection (culture media or 105 TCID50 USA/WA1/2020 isolate, respectively). Mock and SARS-CoV-2 infected hamsters were then given a secondary SARS-CoV-2 infection at 1, 2, 4, or 6 months post-primary infection (n = 14/time point/group). After the primary SARS-CoV-2 infection, hamsters developed anti-spike protein IgG, IgA, and neutralizing antibodies, and these antibodies were maintained for at least 6 months. Upon secondary SARS-CoV-2 challenge, previously SARS-CoV-2 infected animals were protected from weight loss, while all previously mock-infected animals became infected and lost weight. Importantly, despite having high titres of antibodies, one SARS-CoV-2 infected animal re-challenged at 4 months had a breakthrough infection with replicating virus in the upper and lower respiratory tract. These studies demonstrate immunity to SARS-CoV-2 is maintained for 6 months; however, protection may be incomplete and, even in the presence of high antibody titres, previously infected hosts may become re-infected.

SARS CoV-2 Re infection after natural infection compared with previously sero-negative: Descriptive longitudinal study

Background: WHO declared SARS-CoV-2 infection as pandemic on March 11, 2020. As cases recovered, it became important to know the rate of re-infection from the same virus and its severity. Therefore, the study was done to find out re-infection rate among the previously infected individuals. Aim: To find out re-infection rate among already exposed and nonexposed individuals. Materials and Methods: A cohort study was done over 5000 previously serosurveyed individual. They were followed up via telephone. Data was collected using a questionnaire with questions regarding infection post-serosurvey, severity of infection among relatives and vaccination status. Thus information collected was uploaded in Google form. Results: Re-infection rate among previously exposed individuals was 1.2%;at the same time period, 6% of nonexposed individuals got infected. All the re-infection cases were mild, whereas 80.74% of individuals who got infected for the first time had mild symptoms. Exposure to SARS-CoV-2 in relatives who were staying with participants was found to be 3.23% and 4.22% among previously exposed and non-exposed individuals respectively. 17% of previously nonexposed individuals were fully vaccinated, whereas 0.65% of exposed individual got fully vaccinated. Conclusion: Re-infection rate in the study was less and mild on the basis of severity. Infection rate among the nonexposed was at a higher side stating that chances of getting re-infected are much lesser. Previously exposed individuals did not show the same type of interest for vaccination compared to previously nonexposed individuals. © 2022 International Journal of Nutrition, Pharmacology, Neurological Diseases ;Published by Wolters Kluwer - Medknow.

Re-infection in COVID-19: Do we exaggerate our worries?

BACKGROUND: Protective long-term immunity following coronavirus disease 2019 (COVID-19) is unclear. The study evaluated the relationship between the vaccination status and risk factors in the re-infection of patients with a diagnosis of COVID-19 who reported to the Public Health Management System in a province in south-eastern Turkey. METHODS: Patients with positive results for the severe acute respiratory syndrome coronavirus 2 by the real-time reverse transcription polymerase chain reaction (RT-PCR) test in respiratory samples were defined as confirmed cases. Reinfection was diagnosed in cases with COVID-19 real-time RT-PCR positivity, with or without COVID-19-like symptoms, in at least 90 days after the first infection/disease. RESULTS: A total of 58 811 patients with the diagnosis of COVID-19 from March 11, 2020, to August 31, 2021, were included in the study. Re-infection was detected in 421 (0.7%) of all patients. The mean age of the cases was 38.0±16.0 years, and 51% of them were female. Eight (2.0%) of the cases resulted in death due to re-infection. No hospitalization or mortality was observed in fully vaccinated patients. Additionally, none of the mortal cases had completed the vaccination schedule. CONCLUSIONS: We are concerned that the re-infection rates and mortality may increase due to new variant strains. Vaccination is the greatest weapon against progression to critical illness in re-infections, even with existing mutations. Therefore, it is important for those without a full vaccination schedule to be vaccinated, even if they have been previously infected.

Protective Immunity of the Primary SARS-CoV-2 Infection Reduces Disease Severity Post Re-Infection with Delta Variants in Syrian Hamsters.

The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) Delta variant has evolved to become the dominant SARS-CoV-2 lineage with multiple sub-lineages and there are also reports of re-infections caused by this variant. We studied the disease characteristics induced by the Delta AY.1 variant and compared it with the Delta and B.1 variants in Syrian hamsters. We also assessed the potential of re-infection by these variants in Coronavirus disease 2019 recovered hamsters 3 months after initial infection. The variants produced disease characterized by high viral load in the respiratory tract and interstitial pneumonia. The Delta AY.1 variant produced mild disease in the hamster model and did not show any evidence of neutralization resistance due to the presence of the K417N mutation, as speculated. Re-infection with a high virus dose of the Delta and B.1 variants 3 months after B.1 variant infection resulted in reduced virus shedding, disease severity and increased neutralizing antibody levels in the re-infected hamsters. The reduction in viral load and lung disease after re-infection with the Delta AY.1 variant was not marked. Upper respiratory tract viral RNA loads remained similar after re-infection in all the groups. The present findings show that prior infection could not produce sterilizing immunity but that it can broaden the neutralizing response and reduce disease severity in case of reinfection.

The Effect of Varying Interval Definitions on the Prevalence of SARS-CoV-2 Reinfections: A Retrospective Cross-Sectional Cohort Study.

BACKGROUND: We assessed the SARS-CoV-2 reinfection rate in a large patient cohort, and evaluated the effect of varying time intervals between two positive tests on assumed reinfection rates using viral load data. METHODS: All positive SARS-CoV-2 samples collected between 1 March 2020 and 1 August 2021 from a laboratory in the region Kennemerland, the Netherlands, were included. The reinfection rate was analyzed using different time intervals between two positive tests varying between 2 and 16 weeks. SARS-CoV-2 PCR crossing point (Cp) values were used to estimate viral loads. RESULTS: In total, 679,513 samples were analyzed, of which 53,366 tests (7.9%) were SARS-CoV-2 positive. The number of reinfections varied between 260 (0.52%) for an interval of 2 weeks, 89 (0.19%) for 4 weeks, 52 (0.11%) for 8 weeks, and 37 (0.09%) for a minimum interval of 16 weeks between positive tests. The median Cp-value (IQR) in the second positive samples decreased when a longer interval was chosen, but stabilized from week 8 onwards. CONCLUSIONS: Although the calculated reinfection prevalence was relatively low (0.11% for the 8-week time interval), choosing a different minimum interval between two positive tests resulted in major differences in reinfection rates. As reinfection Cp-values stabilized after 8 weeks, we hypothesize this interval to best reflect novel infection rather than persistent shedding.