COVID-19 in Tunisia (North Africa): Seroprevalence of SARS-CoV-2 in the General Population of the Capital City Tunis

Dynamics of SARS-CoV-2 antibodies after natural infection: insights from a study on Pasteur Institute of Tunis employees

This study aimed to assess the kinetics of antibodies against the SARS-CoV-2, following natural infection in a cohort of employees of the Institut Pasteur de Tunis (IPT) and to assess the risk of reinfection over a 12-months follow-up period. A prospective study was conducted among an open cohort of IPT employees with confirmed SARS-CoV-2 infection that were recruited between September 2020 and March 2021. Sera samples were taken at 1, 3, 6, 9 and 12 months after confirmation of COVID-19 infection and tested for SARS-CoV-2-specific immunoglobulin G (IgG) antibodies to the spike (S-RBD) protein (IgG anti-S-RBD) and for neutralizing antibodies. Participants who had an initial decline of IgG anti-S-RBD and neutralizing antibodies followed by a subsequent rise in antibody titers as well as those who tested positive for SARS-CoV-2 by RT-PCR after at least 60 days of follow up were considered as reinfected. In total, 137 individuals were included with a mean age of 44.7 ± 12.3 years and a sex-ratio (Male/Female) of 0.33. Nearly all participants (92.7%) were symptomatic, and 2.2% required hospitalization. Among the 70 participants with three or more prospective blood samples, 32.8% were reinfected among whom 11 (47.8%) reported COVID-19 like symptoms. Up to 12 months of follow up, 100% and 42.9% of participants had detectable IgG anti-S-RBD and neutralizing antibodies, respectively. This study showed that humoral immune response following COVID-19 infection may persist up to 12 months after infection despite the potential risk for reinfection that is mainly explained by the emergence of new variants.

Comparison of long-term anti-RBD SARS-CoV-2 antibody response following different vaccination schemes in Tunisia

AIM

The study aimed to compare long-term vaccine-induced humoral immunity following different vaccines regimens.

METHODS

Anti-S-RBD total antibody levels were measured in blood samples of 167 participants nearly 6 months post-vaccination. Participants had received one; two or four doses of Pfizer vaccine or who received a third dose of mRNA vaccine (Pfizer) and primed with mRNA (Pfizer/Moderna), adenoviral (AstraZeneca/Jonson & Jonson) or inactivated (CoronaVac/Sinopharm) vaccine.

RESULTS

Among all vaccination regimens, fourth dose of Pfizer achieved the highest S-RBD antibody titers. Nevertheless, the third dose of mRNA vaccine primed with adenoviral vaccine achieved the lowest titers of S-RBD antibody. Notably, the group that received a third dose of mRNA primed with two doses of mRNA vaccine exhibited higher S-RBD antibody compared to groups inoculated with a third dose of mRNA and primed with inactivated or adenovirus vaccine.

CONCLUSION

Our data showed the superiority of three mRNA vaccinations compared to third heterologous vaccine (inactivated of adenoviral) including mRNA as booster in terms of humoral immunogenicity. Our findings supporting the use of additional booster shot from a more potent vaccine type such as mRNA vaccines. Nevertheless, due to the limited number of subjects, it is difficult to extrapolate the results of our study to the whole of Tunisian population. Future studies should investigate a larger cohort and other potential correlates of protection, such as cellular immunity and how it is affected by different vaccination schemes after long-term post-vaccination.

Incidence and risk factors of post COVID-19 syndrome: a Tunisian cohort study

BACKGROUND

It has become increasingly clear that SARS-CoV-2 infection can lead to persistent physical and mental health problems lasting weeks or months, requiring prolonged periods of clinical care and increasing the burden on the healthcare system. This phenomenon, known as post COVID-19 syndrome (PCS), is a relatively new condition, its incidence is still unclear and differs between studies.

OBJECTIVES

In this cohort study, we aimed to estimate the incidence of PCS and to identify its risk factors in the Tunisian population.

METHODS

This is a prospective cohort study that enrolled patients diagnosed with COVID-19 from the triage unit of the University Hospital of Monastir, Tunisia. between April 2021 and June 2022. Patients were contacted by phone for a follow-up evaluation of PCS 12- weeks after the diagnosis date.

RESULTS

A total of 1451 individuals diagnosed with COVID-19 during the study period, responded to the follow-up evaluation after 3 months. The incidence of PCS was found to be 44.03% (95% CI [41.47; 46.58]), with fatigue being the most common symptom (21.5%), followed by cognitive impairment (10.3%), including memory loss and difficulty concentrating. Multivariate analysis revealed that the main associated factors to PCS were female gender (RR = 1.54; CI95% [1.30 - 1.82]), pre-existing comorbidities (RR = 1.30; CI95% [1.10 - 1.52]), duration of acute COVID-19 illness (days) (RR = 1.02; CI95% [1.01 - 1.03]), hospitalization (RR = 1.27; CI95% [1.05 - 1.53]), number of COVID-19 episodes (RR = 1.46; CI 95% [1.28 - 1.67]) and patients having receive two or more doses of vaccine prior to COVID-19 infection (RR = 0.82; CI95% [0.70 - 0.96]).

CONCLUSION

Our study allowed to estimate the incidence and identify risk factors of PCS. Recognizing these factors could help to better understand the underlying mechanisms and guide interventions for prevention and management of this condition.

Differences in leucocytes and inflammation-based indices among critically ill patients owing to SARS-CoV-2 variants during several successive waves of COVID-19 pandemic

BACKGROUND/AIM

Inflammatory indices are useful informative markers in assessing the severity of the COVID-19 disease course; however, their involvements during series waves of SARS-CoV-2 virus outbreaks in critical patients with COVID-19 remain unclear. Hence, we aimed to ascertain the changing dynamics of the combined inflammatory indices (NLR, dNLR, CLR, LMR, PLR, SII, and SIRI) and their associations with clinical outcomes in severe COVID-19 patients during serial waves of SARS-CoV-2.

PATIENTS AND METHODS

We retrospectively enrolled 163 severe COVID-19 patients admitted to the ICU during six SARS-CoV-2 waves.

RESULTS

We found that most of patients admitted to the ICU were from the fourth wave. Patients in the fourth wave were considerably younger and had the highest percentage of ARDS than other waves. The highest CRP was found in the first wave, while the lowest in patients admitted in the sixth wave. Although most of the COVID-19 waves were marked with leukocytosis, neutrophilia, and lymphocytopenia, the lowest of both NLR and dNLR were found in the fourth wave "Delta wave" and the lowest of both CLR and SII were observed in "Omicron wave". Interestingly, during most of the COVID-19 waves, the derived combined inflammatory ratio NLR, dNLR, CLR, SII and SIRI were sustained at high levels in fatal cases at the last day of hospitalization, while these indices declined in the alive group at the end of ICU hospitalization. No major difference was identified in lymphocyte count between admission and the last day of hospitalization in both deceased and recovered COVID-19 patients during Delta and Omicron waves. Moreover, patients admitted in the Omicron wave had less severe disease compared to those admitted in the Delta wave. The Kaplan-Meier analysis revealed no significant difference in survival rates or the probability of respiratory failure between six successive COVID-19 waves.

CONCLUSION

Taken together, our results showed marked differences in the alteration of nonspecific inflammation and damage in the adaptive immune response during the six serial SARS-CoV-2 waves. Considering the inflammatory response of infectious diseases, embedding inflammatory indices informative markers into routine clinical testing offers the potential to mitigate the impact of future pandemics of COVID-19 and other infectious diseases.

Seroprevalence of COVID-19 in Oran: Cross-Sectional Study

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was introduced in Algeria in March 2020. This study aimed to estimate the seroprevalence of SARS-CoV-2 infection in Oran, Algeria, and to identify factors associated with seropositivity. This was a cross-sectional seroprevalence study conducted between 7 and 20 January 2021 across all 26 municipalities in the province of Oran. The study employed a random cluster sampling technique stratified by age and sex to select participants from households, who were then administered a rapid serological test. The overall seroprevalence and specific seroprevalences by municipality were calculated, and the number of COVID-19 cases in Oran was estimated. The correlation between population density and seroprevalence was also examined. Among the participants, 422 (35.6%; 95% confidence interval [CI], 32.9 to 38.4) had a positive serological test for SARS-CoV-2, and eight municipalities had seroprevalence rates above 73%. We found a strong positive correlation between population density and seroprevalence (r = 0.795, P < 0.001), indicating that areas with higher population density had higher numbers of positive COVID-19 cases. Our study provides evidence of a high seroprevalence of SARS-CoV-2 infection in Oran, Algeria. The estimated number of cases based on seroprevalence is much higher than the number of cases confirmed by PCR. Our findings suggest that a large proportion of the population has been infected with SARS-CoV-2, highlighting the need for continued surveillance and control measures to prevent further spread of the virus. IMPORTANCE This is the first and only seroprevalence study of COVID-19 conducted in the general population in Algeria prior to the national vaccination campaign against COVID-19. The significance of this study lies in its contribution to our understanding of the spread of the virus in the population before the implementation of the vaccination program.

Dynamics of SARS-CoV-2 seroassay sensitivity: a systematic review and modelling study

BackgroundSerological surveys have been the gold standard to estimate numbers of SARS-CoV-2 infections, the dynamics of the epidemic, and disease severity. Serological assays have decaying sensitivity with time that can bias their results, but there is a lack of guidelines to account for this phenomenon for SARS-CoV-2.AimOur goal was to assess the sensitivity decay of seroassays for detecting SARS-CoV-2 infections, the dependence of this decay on assay characteristics, and to provide a simple method to correct for this phenomenon.MethodsWe performed a systematic review and meta-analysis of SARS-CoV-2 serology studies. We included studies testing previously diagnosed, unvaccinated individuals, and excluded studies of cohorts highly unrepresentative of the general population (e.g. hospitalised patients).ResultsOf the 488 screened studies, 76 studies reporting on 50 different seroassays were included in the analysis. Sensitivity decay depended strongly on the antigen and the analytic technique used by the assay, with average sensitivities ranging between 26% and 98% at 6 months after infection, depending on assay characteristics. We found that a third of the included assays departed considerably from manufacturer specifications after 6 months.ConclusionsSeroassay sensitivity decay depends on assay characteristics, and for some types of assays, it can make manufacturer specifications highly unreliable. We provide a tool to correct for this phenomenon and to assess the risk of decay for a given assay. Our analysis can guide the design and interpretation of serosurveys for SARS-CoV-2 and other pathogens and quantify systematic biases in the existing serology literature.

Development and comparative evaluation of SARS-CoV-2 S-RBD and N based ELISA tests in various African endemic settings

Management of the COVID-19 pandemic relies on molecular diagnostic methods supported by serological tools. Herein, we developed S-RBD- and N- based ELISA assays useful for infection rate surveillance as well as the follow-up of acquired protective immunity against SARS-CoV-2. ELISA assays were optimized using COVID-19 Tunisian patients' sera and prepandemic controls. Assays were further validated in 3 African countries with variable endemic settings. The receiver operating curve was used to evaluate the assay performances. The N- and S-RBD-based ELISA assays performances, in Tunisia, were very high (AUC: 0.966 and 0.98, respectively, p < 0.0001). Cross-validation analysis showed similar performances in different settings. Cross-reactivity, with malaria infection, against viral antigens, was noticed. In head-to-head comparisons with different commercial assays, the developed assays showed high agreement. This study demonstrates, the added value of the developed serological assays in low-income countries, particularly in ethnically diverse populations with variable exposure to local endemic infectious diseases.

Incidence and risk factors of SARS-CoV-2 infection among workers in a public health laboratory in Tunisia

The aim of this study was to measure the extent of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among workers at the Institut Pasteur de Tunis (IPT), a public health laboratory involved in the management of the COVID-19 pandemic in Tunisia, and to identify risk factors for infection in this occupational setting. A cross-sectional survey was conducted on IPT workers not vaccinated against coronavirus disease 2019 (COVID-19). Participants completed a questionnaire that included a history of reverse transcription-polymerase chain reaction (RT-PCR)-confirmed SARS-CoV-2 infection. Immunoglobulin G antibodies against the receptor-binding domain of the spike antigen (anti-S-RBD IgG) and the nucleocapsid protein (anti-N IgG) of the SARS-CoV-2 virus were detected by enzyme-linked immunoassay (ELISA). A multivariate analysis was used to identify factors significantly associated with SARS-CoV-2 infection. A total of 428 workers were enrolled in the study. The prevalence of anti-S-RBD and/or anti-N IgG antibodies was 32.9% [28.7-37.4]. The cumulative incidence of SARS-CoV-2 infection (positive serology and/or previous positive RT-PCR test) was 40.0% [35.5-44.9], while the proportion with asymptomatic infection was 32.9%. One-third of the participants with RT-PCR-confirmed infection tested seronegative more than 90 days postinfection. Participants aged over 40 and laborers were more susceptible to infection (adjusted OR [AOR] = 1.65 [1.08-2.51] and AOR = 2.67 [1.45-4.89], respectively), while tobacco smokers had a lower risk of infection (AOR = 0.54 [0.29-0.97]). The SARS-CoV-2 infection rate among IPT workers was not significantly different from that detected concurrently in the general population. Hence, the professional activities conducted in this public health laboratory did not generate additional risk to that incurred outside the institute in day-to-day activities.