Vaccine effectiveness against COVID-19: A test negative case-control study in Tunisia, August 2021

BACKGROUND

In response to the COVID-19 pandemic, multiple vaccines to protect against COVID-19 disease have been developed rapidly. Precise estimates of vaccine effectiveness (VE) vary according to studies design, outcomes measured and circulating variants. The aim of this study was to evaluate the anti-covid-19 vaccine effectiveness in Tunisia.

METHODS

We conducted a matched case-control study from 2nd to 15th August 2021. Cases and controls were subjects over 60 years of age, selected from the National testing database, regardless vaccine status. A standardized questionnaire was administered for cases and controls to collect information about vaccination status. For cases, vaccination status was defined based on the number of doses received before becoming ill and excludes doses received during the previous two weeks. For matched controls, a reference date based on the case's date of illness onset was defined in order to look at the control's vaccination status before its corresponding case became ill. The odds-ratio was calculated using simple conditional logistic regression. The VE (95 % confidence intervals) was calculated as (1 - odds ratio for vaccination) × 100 %.

RESULTS

A sample of 977 matched peers for age and Gender, were included between August 2, and August 15, 2021. The overall vaccine effectiveness (VE) was 70 % [95 % CI 62.8-75.8 %]. Among our sample, 68.1 % of the male population and 56.4 % of the female population were vaccinated with a VE of 73 % [95 % CI 62.9-80.3 %] and 67 % [95 % CI 55.8-75.3 %] respectively, regardless vaccine scheme (complete or incomplete). VE was higher for the age group [60-70 years[ (72.3 % [95 % CI 62.8-79.3 %]). VE was 77.6 % [95 % CI 70.9-82.8 %] to prevent both symptomatic and asymptomatic forms of the disease. Moreover, in prevention from severe forms (treated with oxygen-therapy or admission to an Intensive-care-unit) VE was 86.6 % [95 % CI 75.6-92.7 %] and 98.4 % [95 % CI [79.2-99.8 %] in prevention from COVID-19 deaths with a complete anti-Covid vaccination scheme.

CONCLUSION

The results of our study showed that the anti-Covid-19 vaccines used in Tunisia are efficient to prevent both SARS-COV-2 infections and severe forms related to the disease. This study provided important data on the performance of vaccines in real-world settings that guide decisions about vaccine sustained use.

Baseline Seroprevalence of SARS-CoV-2 Specific Antibodies in Hot Spot Areas of Great Tunis, up to 3 Months Post Disease Onset in Tunisia

The extent of the SARS-CoV-2 circulation and the COVID-19 epidemic in Tunisia three months after virus circulation was unknown. The aim of this study was to determine the extent of SARS-CoV-2 infection among household contacts of confirmed COVID-19 cases living in Hot spot areas of Great Tunis, Tunisia by estimating the seroprevalence of antibodies anti SARS-CoV-2 and to identify factors associated to seroprevalence at the first stage of the pandemic in order to guide decision making and to constitute a baseline for further longitudinal analysis of protective immunity to SARS-CoV-2. The National Observatory of New and Emerging Diseases (ONMNE), Ministry of Health Tunisia (MoH), with the support of the Office of the World Health Organization Representative in Tunisia and the WHO Regional Office for the Eastern Mediterranean (EMRO)), conducted a household cross-sectional survey on April 2020 in Great Tunis (Tunis, Ariana, Manouba and Ben Arous). The study was based on the WHO seroepidemiological investigation protocol for SARS-CoV-2 infection. SARS-CoV-2 specific antibodies (IgG and IgM) were qualitatively detected using a lateral immunoassay that detect SARS-CoV-2 nucleocapsid protein and administered by the interviewers. The included subjects were confirmed COVID-19 cases and their households contacts resided in hot spot areas (cumulative incidence rate ≥ 10 cases/100,000 inhabitants) of Great Tunis. Results: In total, 1165 subjects were enrolled: 116 confirmed COVID-19 cases (43 active cases and 73 convalescents cases) and 1049 household contacts resided in 291 households. The median age of participants was 39.0 with 31 years' interquartile range (Min = 8 months; Max = 96 years). The sex ratio (M/F) was 0.98. Twenty-nine per cent of participants resided in Tunis. The global crude seroprevalence among household contacts was 2.5% (26/1049); 95% CI 1.6-3.6%, 4.8%; 95% CI 2.3-8.7% in Ariana governorate and 0.3%; 95% CI 0.01%-1.8% in Manouba governorate. In multivariate analysis, the associated factors independently related to seroprevalence were age ≥25 years (aOR = 5.1; 95% CI 1.2-22.0), history of travel outside Tunisia since January 2020 (aOR = 4.6; 95% CI 1.7-12.9), symptomatic illness in the previous four months (aOR = 3.5; 95% CI 1.4-9.0) and governorate of residence (p = 0.02). The low seroprevalence estimated among household contacts in Great Tunis reflect the effect of public health measures early taken (national lockdown, borders closed, remote work), the respect of non-pharmaceutical interventions and the efficacy of COVID-19 contact-tracing and case management at the first stage of the pandemic in Tunisia.

Epidemiological patterns of Hepatitis A infection during the pre-vaccination Era: A population-based survey in Tunisia in 2015

BACKGROUND

In the 1980s, Tunisia was considered a country of high endemicity for Hepatitis A virus (HAV). Since 2000, an epidemiological shift has led to an increased incidence of symptomatic and severe forms of HAV infection.

OBJECTIVE

In 2015, we conducted a cross-sectional nationwide household-based HAV seroprevalence study in the total population regardless of age, sex, or geographical origin using a stratified sampling design in order to make an overview of the HAV epidemiological situation in Tunisia before vaccine implementation.

RESULTS

A total of 6322 individuals were enrolled. The HAV prevalence was 78.8%. The anti-HAV IgG seropositivity rate increases from 16% for ages 5-9 years to 45% for ages 10-14, 67% for ages 15-19, 87% for ages 20-24, and >90% for older age groups, which suggests an age at midpoint of population immunity (AMPI) in late adolescence. It was significantly higher in rural areas (p<10^-3) and varied significantly between and within regions (p<10^-4).

CONCLUSIONS

In this study, although the overall AMPI suggests intermediate endemicity, the regional AMPI varies from intermediate to very high endemicity profiles attributable to different socio-economic determinants and conditions of sanitation and hygiene. Also it provides insights for the best decisions in terms of vaccinations strategies.

[Clinical and epidemiological features of COVID-19-related deaths in Tunisia before the emergence of VOCs (March 2020-February 2021)]

Introduction

the purpose of this study was to describe the clinical and epidemiological features of COVID-19-related deaths in Tunisia notified at the ONMNE (National Observatory of New and emerging Diseases) between 2^nd March 2020 and 28^th February 2021 and to compare COVID-19-related deaths recorded in Tunisia with the international data.

Methods

we conducted a national prospective longitudinal descriptive study of data collected from the National Surveillance System of SARS-CoV-2 infection of the ONMNE, Ministry of Health. All COVID-19-related deaths that occurred in Tunisia between March 2020 and February 2021 were included in this study. Data were collected from hospitals, municipalities and regional health departments. Death notifications were collected from multiple data sources (triangulation): The Regional Directorate of Basic Health Care, the ShocRoom (Strategic Health Operations Center), public and private health facilities, the Crisis Unit of the Presidency of the Government, the Directorate for Hygiene and Environmental Protection, the Ministry of Local Affairs and the Environment, as part of the follow-up of confirmed cases by the ONMNE team, positive RT-PCR / TDR post mortem results.

Results

during this study, 8051 deaths were recorded, corresponding to a proportional mortality of 10.4%. The median age was 73 years, with an interquartile range of 17 years. Sex-ratio (M/F) was 1.8. The crude death rate was 69.1/100 000 inhabitants and fatality rate was 3.5%. The analysis of the epidemic curve showed 2 peaks of deaths on 29^th October 2020 and 22^nd January 2021, with 70 and 86 deaths notified respectively. The spatial distribution of mortality showed that the southern Tunisian region had the highest mortality rate. Patients aged 65 and over were most affected (73.7% of cases) with a crude mortality rate of 570.9/100,000 inhabitants and a fatality rate of 13.7%.

Conclusion

prevention strategy based on public health measures must be reinforced by the rapid deployment of anti-COVID-19 vaccination, especially for people at risk of death.

Identification of transmission chains and clusters associated with COVID-19 in Tunisia

BACKGROUND

The aim of this study was to characterize the transmission chains and clusters of COVID-19 infection in Tunisia.

METHODS

All cases were confirmed by Reverse Transcriptase Polymerase Chain Reaction of a nasopharyngeal specimen. Contact tracing is undertaken for all confirmed cases in order to identify close contacts that will be systematically screened and quarantined. Transmission chains were identified based on field investigation, contact tracing, results of screening tests and by assessing all probable mode of transmission and interactions.

RESULTS

As of May 18, 2020, 656 cases out of a total of 1043 confirmed cases of Coronavirus disease 2019 belong to 127 transmission chains identified during the epidemic (mean age 42.36 years, Standard deviation 19.56 and sex ratio 0.86). The virus transmission is the most concentrated in the governorate of Tunis (31.5%), Ariana (10.2%) and Ben Arous (10.2%). Virus transmission occurred 50 times (9.72% of secondary transmission events) between two different governorates. A maximum of seven generations of secondary infection was identified, whereas 62% of these secondary infections belong the first generation. A total of 11 "super spreader" cases were identified in this investigation. Four large clusters have been identified. The evolution of secondary cases highlighted two peaks: one in 2nd April and a second in 16 th April whereas imported cases caused local transmission of virus during the early phase of the epidemic.

CONCLUSION

Correct contact tracing and early active case finding is useful to identify transmission chains and source of infection in order to contain the widespread transmission in the community.

Impact of contact tracing, respect of isolation, and lockdown in reducing the number of cases infected with COVID-19. Case study: Tunisia's response from March 22 to May 4, 2020

Background

Coronavirus disease 2019 (COVID-19) has spread rapidly across the world. Tunisia reacted early to COVID-19, resulting in a low number of infections during the first wave of the pandemic. This study was performed to model the effects of different interventions on the evolution of cases and to compare these with the Tunisian experience.

Methods

A stochastic transmission model was used to quantify the reduction in number of cases of COVID-19 with the interventions of contact tracing, compliance with isolation, and a general lockdown.

Results

In the model, increasing contact tracing from 20% to 80% after the first 100 cases reduced the cumulative number of infections (CNI) by 52% in 1 month. Similarly, increased compliance with isolation from 20% to 80% after the first 100 cases reduced the CNI by 45%. These reductions were smaller if the interventions were implemented after 1000 cases. A general lockdown reduced the CNI by 97% after the first 100 cases. Tunisia implemented its general lockdown after 75 cases were confirmed, which reduced the cumulative number of infected cases by 86% among the general population.

Conclusions

This study shows that the early application of critical interventions contributes significantly to reducing infections and the evolution of COVID-19 in a country. Tunisia’s early success with the control of COVID-19 is explained by its quick response.

Estimating transmission dynamics and serial interval of the first wave of COVID-19 infections under different control measures: a statistical analysis in Tunisia from February 29 to May 5, 2020

BACKGROUND

Describing transmission dynamics of the outbreak and impact of intervention measures are critical to planning responses to future outbreaks and providing timely information to guide policy makers decision. We estimate serial interval (SI) and temporal reproduction number (Rt) of SARS-CoV-2 in Tunisia.

METHODS

We collected data of investigations and contact tracing between March 1, 2020 and May 5, 2020 as well as illness onset data during the period February 29-May 5, 2020 from National Observatory of New and Emerging Diseases of Tunisia. Maximum likelihood (ML) approach is used to estimate dynamics of Rt.

RESULTS

Four hundred ninety-one of infector-infectee pairs were involved, with 14.46% reported pre-symptomatic transmission. SI follows Gamma distribution with mean 5.30 days [95% Confidence Interval (CI) 4.66-5.95] and standard deviation 0.26 [95% CI 0.23-0.30]. Also, we estimated large changes in Rt in response to the combined lockdown interventions. The Rt moves from 3.18 [95% Credible Interval (CrI) 2.73-3.69] to 1.77 [95% CrI 1.49-2.08] with curfew prevention measure, and under the epidemic threshold (0.89 [95% CrI 0.84-0.94]) by national lockdown measure.

CONCLUSIONS

Overall, our findings highlight contribution of interventions to interrupt transmission of SARS-CoV-2 in Tunisia.

Prevalence and risk factors of hepatitis B in Tunisia

Background

Hepatitis B virus (HBV) infection is a major public health problem. Data related to epidemiology, distributions and outcomes of VHB infections in Tunisia remains scarce. This work aimed to study the prevalence of HBV infections and their distribution as well as the main risk factors associated to HBV infection.

Methods

Our study was a cross-sectional household- based study carried out among a representative sample of 22 275 from January 2014 to December 2015. Sampling was based on the National Census of 2014. For data collection, questionnaires were administrated by trained investigator and blood samples were sent to the Reference laboratory for analysis of HBV markers.

Results

Among 21720 surveyed subjects, 19663 subjects had a laboratory tests and the serological results reached to 19155. Overall prevalence of HBs Ag was 1.7% [1.6-1.9]. Prevalence of HBsAg was significantly higher in men (2.1% against 1.4%; p &lt; 10-3), in age group more than 20 years (2.1% against 0.1% p ≪10-3) and in the Central region (2.3%; p &lt; 10-3). Among the associated risk factors in univariate analysis were chronic dialysis, dental care, surgical intervention, hospitalization, traditional circumcision, scarification and multiple sexual partners. Multivariate analysis showed that male gender, age over 20 years, center and south regions, hospital follow-up of a chronic pathology and having a family member chronic carrier of HBs Ag were the associated risk factors of HBV infection and vaccination was the only protective factor.

Conclusions

Our study allowed to have a clear estimate of the national prevalence of HBsAg and to classify Tunisia as a country of low endemicity of Hepatitis B. This decline is mainly due to the introduction of vaccination since 1995 and the improvement of the health system. However, more efforts should be paid to reduce nosocomial transmission and traditional high-risk behaviors.

Key messages

Tunisia has become a country of low endemicity for hepatitis B. This was a result to the introduction of vaccination since 1995.

Impact of hepatitis B vaccine in Tunisia 20 years after its introduction

Introduction

Vaccination against hepatitis B represents the most effective preventive measure to reduce the global impact of this infection. In Tunisia hepatitis B vaccination was introduced for health professionals in 1992 and for the general population in 1995. The objectives of this study were to evaluate the impact of vaccination twenty years after its introduction.

Methods

It was a descriptive study of data provided by the national survey of prevalence of Hepatitis B in Tunisia, which was a household-based study conducted in 2015. Blood samples sent to the reference laboratory to test markers of hepatitis B virus infection. The Vaccine effectiveness rate was calculated using the following formula: VE = 1 - Odds-ratio (OR), where OR = ratio of odds of being vaccinated among subjects with positive HBsAg test results to the odds of being vaccinated among subjects with negative HBsAg test results.

Results

Approximately a quarter of our population reported having been vaccinated against HBV, a coverage rate of 26.9%. Among subjects above 20 years of age, this rate was 85.3%. Besides, 83.7% of vaccinated subjects had received the three required doses of the HBV vaccine. Analysis of vaccination status by great regions of the country showed that the vaccination coverage rate was higher in the southern region. Regarding HBsAg prevalence, the rate was significantly higher among unvaccinated subjects 0.3% vs 2.2% in those vaccinated (OR = 0.11 [0.07-0.18]). We found that among vaccinated subjects, the serologic response rate at vaccination was only 63.2% which represented 16.2% of the total population. The vaccine effectiveness indicated that vaccination reduced by 88.6% the risk of HBV infection.

Conclusions

These results demonstrate that vaccination against hepatitis B introduced in the national immunization schedule since 1995 has reduced the infection although the vaccination coverage rate remains below 90%.

Key messages

Importance of vaccination that reduced by 88.6% the risk of HBV infection. More effort required to raise awareness about vaccination against HBV.

Effect of outdoor air pollution on respiratory deseases in the District of Tunis

Background

Asthma and Chronic Obstructive Pulmonary Disease (COPD) are the two most common chronic obstructive pulmonary diseases worldwide. The objective of this study was to analyze the relation between the daily levels of air pollution indicators and the number of emergency department visits (EDV) for asthma and COPD exacerbation in the District of Tunis.

Methods

We conducted a retrospective ecological study. We collected daily morbidity data from the emergency register of Ariana Mami Hospital from 1 January 2007 to 31 December 2014. We investigated the association between daily EDV for asthma or COPD exacerbation and daily concentrations levels of air pollutants by simple Pearson correlation and by binomial negative regression using generalized linear models (GLM).

Results

For morbidity data, we recorded 19127 EDV for asthma (10771, 56.3%) and COPD exacerbation (8356, 43.7%) between 2007 and 2014. We observed a rising trend in the number of EDV for COPD since 2007 with winter seasonality. Regarding the profile of air pollution in the study region, we have exceeded the thresholds of all standards for PM10, exceeding the Canadian standard for O3. However, no threshold exceeded for NO2 and SO2. In the univariate analysis, there was a positive correlation between the daily number of EDV for asthma and COPD exacerbation and NO2 ambient concentration (r = 0.121, p &lt; 10-3) and O3 level (r = 0.066, P &lt; 10-3). Multivariate analysis showed a significant positive association between the daily number of EDV for asthma and COPD exacerbation and NO2 daily concentration (Adjusted OR = 1.033, CI = [1.011 - 1.055], P &lt; 10-3) with a delayed effect of 10 days for NO2 and 12 days for O3.

Conclusions

The exacerbation of asthma and COPD was correlated to the NO2 outdoor air concentration level, with an immediate and other delayed effect of 10 days, also with the 12-day lag from the elevation of O3.

Key messages

Ambient air pollution is a major risk factor for respiratory health. Reducing NO2 emissions could decrease morbidity and direct health care costs of respiratory diseases.

Observational study of vaccine effectiveness 20 years after the introduction of universal hepatitis B vaccination in Tunisia

OBJECTIVES

The objectives of this study were to estimate the national prevalence of hepatitis B infection in Tunisia using data from a nationwide survey, to compare results with those obtained in 1996 survey and to evaluate the impact of vaccination twenty years after its introduction.

METHODS

A National household-based cross sectional and serological survey was undertaken in 2015 from randomly selected districts using two-stage sampling. Data collection was performed using standardized and pretested questionnaires and collected blood samples were tested for markers of hepatitis B virus infection.

RESULTS

National point prevalence of Hepatitis B surface antigen was 1.7% (95% CI [1.6-1.9%]). The highest prevalence was found in the Center and South regions with respectively 2.3% (95% CI [2.0-2.7%]) and 2.2% (95% CI [1.8-2.8%]). Vaccine effectiveness (VE) was 88.6% (95% CI [81.5-93.0%]) and was higher among population aged less than 20 years 96.1% (95% CI [70.1-99.5%]) than those aged more than 20 years 59.0% (95% CI [32.0-75.3%]). VE was 85.6% (95% CI [65.8-93.9%]) is hyper-endemic areas and 89.1% (95% CI [80.3-94.0%]) in meso-endemic and hypo-endemic areas.

CONCLUSIONS

The prevalence of Hepatitis B surface antigen decreased compared to previous estimations and classify Tunisia as a low endemic country as result to the introduction of vaccination since 1995.

Modeling zoonotic cutaneous leishmaniasis incidence in central Tunisia from 2009-2015: Forecasting models using climate variables as predictors

Transmission of zoonotic cutaneous leishmaniasis (ZCL) depends on the presence, density and distribution of Leishmania major rodent reservoir and the development of these rodents is known to have a significant dependence on environmental and climate factors. ZCL in Tunisia is one of the most common forms of leishmaniasis. The aim of this paper was to build a regression model of ZCL cases to identify the relationship between ZCL occurrence and possible risk factors, and to develop a predicting model for ZCL's control and prevention purposes. Monthly reported ZCL cases, environmental and bioclimatic data were collected over 6 years (2009-2015). Three rural areas in the governorate of Sidi Bouzid were selected as the study area. Cross-correlation analysis was used to identify the relevant lagged effects of possible risk factors, associated with ZCL cases. Non-parametric modeling techniques known as generalized additive model (GAM) and generalized additive mixed models (GAMM) were applied in this work. These techniques have the ability to approximate the relationship between the predictors (inputs) and the response variable (output), and express the relationship mathematically. The goodness-of-fit of the constructed model was determined by Generalized cross-validation (GCV) score and residual test. There were a total of 1019 notified ZCL cases from July 2009 to June 2015. The results showed seasonal distribution of reported ZCL cases from August to January. The model highlighted that rodent density, average temperature, cumulative rainfall and average relative humidity, with different time lags, all play role in sustaining and increasing the ZCL incidence. The GAMM model could be applied to predict the occurrence of ZCL in central Tunisia and could help for the establishment of an early warning system to control and prevent ZCL in central Tunisia.