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 Table of Contents  
Year : 2022  |  Volume : 9  |  Issue : 1  |  Page : 33-37

COVID immunity in the Angolan population: Serological study with Abbott COVID-19 IgG/IgM Rapid Test and serological mini VIDAS BIOMERIEUX test

1 International SOS Talatona Clinic, Luanda, Angola
2 National Institute for Health and Medical Research (INSERM), University of Limoges, CHU Limoges, IRD, U 1094, GEIST, Limoges, France
3 CMS Total, Luanda, Angola
4 Paz Flor Medical Center, Luanda, Angola

Date of Submission04-Nov-2021
Date of Acceptance03-Mar-2022
Date of Web Publication23-Mar-2022

Correspondence Address:
Dr. Renata Almeida
International SOS Talatona Clinic, OfficeRua S10 Sector Talatona, Zona CC-B2, Luanda.
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mgmj.mgmj_91_21

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Background: The numbers of severe COVID cases and COVID-related deaths on the African continent are lower than expected. We hypothesize that this paradox may be due to the achieved immunity in black Africans. Materials and Methods: A prospective study was conducted on Angolan people who performed the Panbio Abbott COVID-19 IgG/IgM Rapid Test in a health unit in Luanda. One hundred randomly selected subjects in those with positive immunoglobulin G (IgG) underwent the serological mini VIDAS BIOMERIEUX test. Results: In our population study (2409 subjects), 791 (32.83%) had positive IgG at the Panbio Abbott COVID-19 test. One hundred were randomly selected. The mean age was 39.55, and 96% were males. The positivity to IgG was validated in 72 subjects at the mini VIDAS BIOMERIEUX test. Conclusion: These results support our hypothesis that in the Angolan/African population a previously achieved immunity may be one of the reasons why this continent was not affected by COVID-19 as expected.

Keywords: Angolan, COVID-19, COVID-19 test, IgG serology, IgM serology, immunity

How to cite this article:
Almeida R, Desormais I, Taton P, Morales E, Reis A, Simba Y. COVID immunity in the Angolan population: Serological study with Abbott COVID-19 IgG/IgM Rapid Test and serological mini VIDAS BIOMERIEUX test. MGM J Med Sci 2022;9:33-7

How to cite this URL:
Almeida R, Desormais I, Taton P, Morales E, Reis A, Simba Y. COVID immunity in the Angolan population: Serological study with Abbott COVID-19 IgG/IgM Rapid Test and serological mini VIDAS BIOMERIEUX test. MGM J Med Sci [serial online] 2022 [cited 2022 May 20];9:33-7. Available from: http://www.mgmjms.com/text.asp?2022/9/1/33/340597

  Introduction Top

Due to fragile health systems, lack of access to preventive measures, barriers to testing, and potentially vulnerable populations, a high number of severe cases and deaths were expected on the African continent. Nevertheless, according to the World Health Organization (WHO) reports, Africa remains the least affected region, with 1.5% of the world’s reported coronavirus disease-2019 (COVID-19) cases and 0.1% of the world’s deaths.[1]

Many hypotheses have been suggested for this paradox, including the sensitivity of the virus to ambient temperature, Africa’s comparatively young population, lower rates of obesity, and familiarity with infectious disease outbreaks.[1] Low levels of testing were also been incriminated as artificially lower apparent infection rates. The average age on the African continent is 19.7 years, and contagion rates may also be underestimated as most asymptomatic cases occur among young people and the mortality rate is higher in the elderly.[2]

Moreover, preventive measures such as travel restrictions, school closures also were applied in advance to the first COVID-detected case in Black Africa.[2] Among all these hypotheses, the most plausible seems to be the population young age and the general population immunity to other pathogens since childhood. On January 20, 2020, Angola numbered 19,093 COVID cases and 444 COVID-related deaths.[3]

A COVID-19 antibody test can detect if a person has immunoglobulin M (IgM) or immunoglobulin G (IgG) antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19. The presence of IgM or IgG identifies people who may have been infected with the SARS-CoV-2 virus or have recovered from the COVID-19 infection.[2] Two tests are available for the screening and diagnosis of COVID infection: the Panbio Abbott COVID-19 IgG/IgM Rapid Test for screening and the mini VIDAS SARS-COV-2 IgM and IgM for serological confirmation.[4],[5]

The results of the Abbott Rapid Test on venous plasma and finger stick whole blood are available in 10–20 min, with very high sensitivity (74.4%) and specificity (99.9%).[6] The mini VIDAS SARS-COV-2 IgM and VIDAS SARS-COV-2 IgG test is an automated immunoassay system based on the enzyme-linked fluorescent assay (ELFA). It rapidly (less than 30 min) identifies previous exposure to SARS-CoV-2 with high sensitivity (88.6% to IgG 8–15 days after positive polymerase chain reaction (PCR) and 96.6% after ≥ 16 days) and specificity (99.9%).[7]

SARS-COV-2 IgG antibodies can be detected up to 90 days after acute phase infection, even in mild cases. Patients with severe COVID-19 appear to have higher levels of antibodies than those with mild/asymptomatic cases, but the kinetics of antibody levels are similar across all cases.[8] To better explain the dynamic of the COVID epidemic in Africa, we hypothesize that this paradox is due to the achieved immunity. No study specifically analyzed, before, the prevalence of positive IgG among people in the general population.

Our study aimed to describe and confirm the prevalence of IgG-positive subjects among Angolan people in Luanda.

  Materials and methods Top

Our prospective study was conducted in the COVID testing and vaccination health center located on Paz Flor Morro Bento in Luanda. We aimed to determine the prevalence of COVID-19 immunity among young Angolan people with no previous symptomatic infection.

Study design

The study population included, successively, all Luanda residents systematically tested to COVID-19 before reaching the oil platforms for work. Previous COVID diagnosis or Refusal to participate was the exclusion criterion. Oral consent was obtained before inclusion. Data were collected through a face-to-face interview, a clinical examination, and laboratory tests.


The study obtained the approval of the National Ethics Review Committee (NEC) from Angola. The research reported in the paper was undertaken in compliance with Declaration of Helsinki.

Data collection and definitions

The administered questionnaire included exclusively demographic characteristics: age, gender, and COVID-19 infection signs and symptoms. First, the rapid test, Panbio Abbott COVID-19 IgG/IgM Rapid Test was performed. Second, 100 IgG-positive subjects were randomly selected for the mini VIDAS serology to confirm the COVID serological immunity.

Statistical analysis

Data were analyzed by using the statistical program Stata 12 (StataCorp, College Station, Texas). The Student’s t test or the Mann–Whitney test was used for the comparison of the continuous variables and the chi-square test or Fisher exact test for the comparison of the categorical variables. To determine independent risk factors associated with COVID, a multivariable logistic regression model including a backward stepwise procedure was performed. The level of significance for all the statistical analyses was set at P < .05 and interactions were checked.

  Results Top

From August to December 2020, 2409 subjects, mean age 39.6 years performed the Panbio Abbott COVID-19 IgG Rapid Test [Figure 1]. Approximately 96% were men. There were no refusals to participate. Among the 2409 subjects, 791 (32.8%) had positive IgG at the Rapid Test and only 28 had positive IgM. The serological mini VIDAS BIOMERIEUX test was secondly performed on one hundred randomly selected positive IgG subjects. 72% were confirmed IgG+ [Figure 1].
Figure 1: Total population and IgG+ at Panbio Abbott Rapid Test and confirmed IgG- at mini VIDAS BIOMERIEUX test

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Among the 791 positive IgG subjects, 11% were 20–29 years old, 46% were 30–39 years old, 28% were aged from 40 to 49, and 15% were 50 years and older (the oldest subject was 57 years). The IgG positivity mini VIDAS BIOMERIEUX test was confirmed at 72% but the percentage of positivity varied from one age group to another [Figure 2]. These results were statistically different for subjects aged 50 or more (only 47% of positivity, P < .0001) [Figure 2], but comparable for the others.
Figure 2: IgG+ subjects by age group (%) and positive results (%) at mini VIDAS BIOMERIEUX test

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There was no actual history of signs or symptoms of COVID-19 among the IgG+ population (fever, headache, cough, rhinitis, digestive symptoms). The 28 IgM+ subjects were excluded from the statistical analyses. Their main characteristics were comparable (97% men, mean age 39.4 ± 6.8), asymptomatic.

  Discussion Top

Our study results confirm the previous COVID-19 immunity in the Luanda adult population which could partially explain why the Sub-Saharan African continent remains the least affected region in the world.

To the best of our knowledge, this is the first study specifically focused on the African COVID-19 immunity, carried out at an early stage of the pandemic: only a few months (5–9 months) after the first detected COVID-19 case in Luanda (March 21). Therefore, our results lead us to believe that immunity was related to the background of this population and not due to a previous COVID-19 infection. This hypothesis is also supported by the lack of concomitant or history of COVID-19-related signs or symptoms.

The weakness of our study is the selected population: workers on oil platforms, generally men aged 20 and more. The study population has been justified by easier access to the test (too expensive and not available in the general population). The lack of women and younger subjects does not allow a complete analysis but we do believe that the test’s results might be extrapolated to young adults in the general population as the test was performed before reaching the platforms after at least one month ashore and not to their return. Also as only simple demographic characteristics were available, further studies in the general population should be done to analyze gender differences and the impact of chronic pathologies.

In our study, only 47% of the oldest age group was confirmed with the serological test. This might be due to a false positive on Panbio Abbott Rapid Test IgG or a false negative on mini VIDAS IgG. A false-positive detection of IgG SARS-CoV-2 antibody can be because of endogenous factors like rheumatoid factor, heterophil antibody, lysozyme, and cross-antigens. Rheumatoid Factor (RF)may appear in the blood of autoimmune diseases, such as rheumatoid arthritis, infectious diseases, and even healthy people. In SARS-CoV-2 antibody detection, RF can nonspecifically bind to the specific antibody fragment crystallizable (Fc) segment coated on the solid-phase carrier and the labeled antibody Fc segment, resulting in a nonspecific detection signal, causing false positive). Heterophil antibody is a type of cross-reactive immunoglobulin secreted by the human immune system, lacking animal serum or animal immunoglobulin stimulation can stimulate the immune activity of the target antigen in the immune response, attach to the capture antibody and label antibody, and thereby interfere. Lysozyme is widely present in various human tissues, with an isoelectric point of pH 11, and has a strong binding ability with substances having a lower isoelectric point. The isoelectric point of immunoglobulin is approximately 5, so lysozyme can form a bridge between the labeled IgG and the coated IgG in immunoassays, resulting in false-positive reactions. Cross-antigens are similar epitopes between two antigens from different sources. The antibodies produced by certain determinants can bind to the corresponding epitopes on their surface and react with similar epitopes of other antigens. At present, a large number of studies have shown that there are N protein and S protein immune cross-reactions between coronaviruses in the same subgenus or different subgenuses.[9]

A false negative on mini VIDAS IgG can occur if the quantity of the anti-SARS-CoV-2 antibodies present in the specimen is below the detection limits of the assay, or the antibodies that are detected are not present during the stage of disease in which a sample is collected. Patient specimens may be negative if collected during the early (pre-seroconversion) phase of illness or due to a decline in titer over time. In addition, the immune response may be depressed in elderly, immunocompromised, or immunosuppressed patients. These facts may be the causes of the results obtained in this population.[5]

There are seven types of coronaviruses capable of infecting humans. Among these, three can cause severe acute respiratory disease: SARS-CoV-2, SARS-CoV, and MERS-CoV. In contrast, the other four types, classified as genotypes, are considered endemic, usually causing only mild infection of the upper respiratory tract. They are called 229E, NL63, OC43, and HKU1. Because of the sequence identity between the common flu-causing coronaviruses in humans (HKU1, OC43, NL63, and 229E) and SARS-CoV-2, cross antigenicity should be considered, and this can be one of the reasons for the immunity in African people.[10]

In this study, we also conducted the mini VIDAS IgG BIOMERIEUX tests on 100 people in the population who had IgG positive on the Panbio Abbott COVID-19. We found that 72% of these also had IgG in this test, this may be due to false positives resulting from the Abbot test, and however, we continue to find high immunity in the African population. We decided to apply this test because it´s a compact and automated immunoassay system based on ELFA principles (fluorescence immunoenzymatic test) and has more sensitivity and validated the tests.

  Conclusion Top

COVID-19 infection history could be important for future medical management, and in this study, we confirm that immunity already exists in a certain African population, and this may be one of the causes for the lower impact of COVID-19 on this continent. However, we stay with these outstanding questions about how the antibodies reflect protective immunity, the durability of antibodies, and the necessity for protection from reinfection. Another issue remains, why the African population already has immunity. It is due to cross-match with other coronaviruses, due to immunity from other diseases, your immune system can be because of a lot of causes or a mix of them. Because of this, further studies are needed in this population to better understand this situation. It would also be interesting to conduct serological studies in rural and urban environments in Africa.

Ethical policy and institutional review board statement

The study obtained the approval of the National Ethics Review Committee (NEC) from Angola. The research reported in the paper was undertaken in compliance with Declaration of Helsinki.


We are grateful to the entire team working at Paz Flor Medical Center (Luanda, Angola) who supported us and worked with us all this time. In this pandemic time, everything has become easier with this team.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

The Lancet. COVID-19 in Africa: No room for complacency. Lancet 2020;395:1669.  Back to cited text no. 1
West R, Kobokovich A, Connell N, Gronvall GK. COVID-19 antibody tests: A valuable public health tool with limited relevance to individuals. Trend Microbiol 2021;29:214-23.  Back to cited text no. 2
Africa Centre for Disease Prevention and Control (CDC). African Union Rolls Out Partnership to Accelerate COVID-19 Testing; 2020. Available from: https://africacdc.org/news-item/african-union-rolls-out-partnership-to-accelerate-covid-19-testing/. [Last accessed on 2020 Jan 26].  Back to cited text no. 3
PANBIO™ COVID-19 IgG/IgM Rapid Test Device VIDAS® SARS-COV-2 Dois testes de imunoensaio para detetar anticorpos IgM & IgG. Available from: https://www.biomerieux.pt/produto/vidasr-sars-cov-2. [Last accessed on 2020 Jan 26].  Back to cited text no. 4
Scale-up Covid-19 Antibody Testing. Available from: https://www.globalpointofcare.abbott/en/product-details/panbio-covid-19-igg-igm-antibody-test.html. [Last accessed on 2020 Jan 26].  Back to cited text no. 5
Norwegian Directorate of Health. COVID-19 Pandemic: Evaluation of Abbot’s Panbio COVID-19 Rapid Antigen Test in Norway. Oslo: Norwegian Directorate of Health; 2020. Available from: https://www.helsedirektoratet.no/rapporter/evaluation-of-abbots-panbio-covid-19-rapid-antigen-test-in-norway. [Last accessed on 2020 Dec 3].  Back to cited text no. 6
Wolff F, Dahma H, Duterme C, Van den Wijngaert S, Vandenberg O, Cotton F, et al. Monitoring antibody response following SARS-CoV-2 infection: Diagnostic efficiency of 4 automated immunoassays. Diagn Microbiol Infect Dis 2020;98:115140.  Back to cited text no. 7
Moradi G, Mohamadi Bolbanabad A, Ahmadi S, Aghaei A, Bahrami F, Veysi A, et al. Persistence assessment of SARS-CoV-2-specific igg antibody in recovered COVID-19 individuals and its association with clinical symptoms and disease severity: A prospective longitudinal cohort study. Int Immunopharmacol 2021;98:107893.  Back to cited text no. 8
Ye Q, Zhang T, Lu D. Potential false-positive reasons for SARS-CoV-2 antibody testing and its solution. J Med Virol 2021;93:4242-6.  Back to cited text no. 9
Hu B, Guo H, Zhou P, Shi ZL. Characteristics of SARS-CoV-2 and COVID-19. Nat Rev Microbiol 2021;19:141-54.  Back to cited text no. 10


  [Figure 1], [Figure 2]


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