The novel coronavirus took the world by surprise in December 2019, when several acute atypical respiratory tract infections were noticed in China and subsequently spread globally. [1] It caused a severe multisystemic disease, subsequently named the coronavirus disease 2019 (COVID-19). Within 36 months, 696 million cases and 6.6 million deaths had been reported worldwide from COVID-19 complications. A significant number of these cases (9.4 million) were reported in Africa [2] and Nigeria was not excluded from these complications.

The initial global response was focused on adults particularly in developing countries, as most of the complications were among adults. However as the pandemic progressed, more infections were reported in children and adolescents. [3] These adolescents mainly had asymptomatic or subclinical COVID-19 infections. Despite their subclinical presentations, they could transmit the virus making them a risk to other age groups, especially the elderly, younger children, and immunocompromised. [4] These adolescents are also at risk of long-term complications, particularly the Long COVID which has been seen in adolescents regardless of the severity of the disease. The Global response to the pandemic included travel restrictions (the lockdown), physical distancing, use of face masks, hand hygiene and eventually, vaccination. Many countries including Nigeria excluded adolescents and children from the COVID-19 vaccination Programme. In Nigeria where a quarter of the estimated 213 million population are adolescents, COVID vaccination in this age group is still restricted to those needing it for international travel and education. As of 2021, with increasing vaccination coverage, many countries relaxed the very stringent COVID-19 prevention requirements. The important question of whether COVID-19 had abated, particularly in the important adolescent population who received very little attention, was however left unanswered. Till-date, pockets of cases are still being reported. In Benue State, North-Central Nigeria, 25 new cases have been alluded to by the World Health Organization (WHO). [5] This suggests ongoing transmission.

Factors such as age, gender, socioeconomic status, and nutritional status that have been identified in some studies as being associated with seropositivity have not been comprehensively studied in adolescents. [6] Age and sex-disaggregated data from low and middle-income countries like Nigeria is limited. [7] Data from the United States Centre for Disease Control (CDC) noted that mortality arising from complications in children, was disproportionately higher in adolescents, Africans, and Hispanics. This suggests a need for further research in these subgroups. [8][9][10] In this study, we examined the pattern of exposure in Nigerian adolescents as documented by seropositivity and determined its association with age, gender, socioeconomic class, overcrowding, school type and nutritional status.

STUDY DESIGN: This was a cross-sectional study recruiting study participants from 6 secondary schools across 10 wards in Benin City, South-South Nigeria. The study was conducted between August and December 2022. The study population was made up of apparently healthy adolescents aged 10 to 19 years who met the inclusion criteria. Participants were eligible for enrolment if they met the following criteria: they attended one of the participating secondary schools, were between the ages of 10 and 19 years, their parent or legal guardian gave informed consent to participate, and the child gave their assent. Children with a prior COVID-19 positive diagnosis, children whose parents did not give consent and those outside the stipulated age were excluded.

Ethical clearance was obtained from the Health Research and Ethical Committee of the University of Benin Teaching Hospital (UBTH) protocol number: ADM/E22/A/VOL.1457, (see Appendix 1) and written permission was obtained from the Edo State Ministry of Education and Edo State Universal Basic Education Board (SUBEB). Participants were assured of confidentiality.

SAMPLING AND DATA COLLECTION: A multistage sampling technique was used. We randomly selected 3 out of the 10 wards in the selected LGA, and 30% of the secondary schools in these wards were randomly selected. The total student population in the 6 selected schools was determined from the school registers, and our sample size of 270study participants was distributed by proportion among the selected schools. A total of 270 students were recruited.

Sociodemographic data was collected from the study participants using a pretested modified WHO proforma for population-based age-stratified seroepidemiological studies for SARS-CoV-2. [11][12] The questionnaire was interviewer-administered.

LABORATORY ANALYSIS: Capillary blood samples were collected from the study participants by the research team and analysed using a lateral flow immunoassay device; the Unscience^R COVID IgG/IgM rapid test device, an immunochromatographic test for the qualitative detection of IgM and IgG antibodies to SARS CoV2. The manufacturers reported a sensitivity of 98.81% (95% CI: 97.25%, 99.61%), and a specificity of 98.02% (95%CI: 97.05%,98.74%). Test results were classified into one of five categories: Negative, IgG positive alone, IgM positive alone, IgG and IgM positive or invalid. Invalid or ambiguous test kits were discarded, and sample collection from the participant was repeated.

STATISTICAL ANALYSIS: Data obtained was analysed using Statistical Package for Social Sciences (SPSS) spreadsheet version 28. Overcrowding in homes was defined as; a couple plus a child <12 years or two adults (not in a relationship) of the opposite sex sleeping in the same room. [13][14] while overcrowding in classes was defined as more than 35 students to one teacher in a standard classroom. [15]

The primary outcome was serostatus of the study participants. The relationship between sociodemographic variables and serostatus was analysed using the chi-square test and Fisher’s Exact test where applicable.The positive predictors of serostatus were finally determined using a multiple logistics regression model. Statistical significance was set at p < 0.05.

A total of two hundred and seventy (270) participants between the ages of 10 to 19 years were recruited from both public and private secondary schools. Comparisons of the sociodemographic characteristics of the participants were made based on their school type (Table 1). Adolescents were classified into age groups in line with the WHO classification. [16] Early adolescents accounted for 54.1% (146), middle adolescents 30% (81) and late adolescents 15.9% (43) of the study population. The study participants consisted of 111 (41.1%) males and 159 (58.9%) females, giving a male: female ratio of 1:1.4. There were 112 (41.5%) study participants from the lower socioeconomic class (SEC), 105 (38.9%) from the middle, and 53 (19.6%) from the upper socioeconomic class. None of the participants had received COVID-19 vaccination.

Table1. Sociodemographic characteristics of study participants.

χ²: chi-square test, p: probability. *: p < 0.05 (Significant p-value).

Most of the students in public schools 101 (68%) were from low socioeconomic classes compared to those in private schools who were mostly from middle 66 (53.7%) and upper 46 (37.4%) socioeconomic classes. The difference in the socioeconomic class between study participants in public and private schools was statistically significant. (χ² = 106,672, p = 0.001).

Overcrowding in homes was defined as; a couple plus a child < 12 years or two adults (not in a relationship) of the opposite sex sleeping in the same room. [13][14] Overcrowding in classes was defined as more than 35 students to one teacher in a standard classroom. [15] A total of 149 students lived in overcrowded homes, of which 96 (64.4%) were from public schools, while 53 (35.6%) were from private schools. This difference was statistically significant. (χ² = 13.365, p = 0.001). There were significantly more overcrowded classrooms in public schools compared to private schools. (χ² = 95.788, p = 0.001).

The mean weight and height of students in public schools were significantly higher than those in private schools as shown in Table2 (t = 2.031, p = 0.043 and 3.302, p < 0.001 respectively).

This study focused on adolescents, who make up a large percentage of the population and can serve as a reservoir for transmission. The seroprevalence obtained in this study was 45.9%. This suggests a high seropositivity to SARS-CoV-2 among adolescents in this region and is reflective of the significantly high ongoing transmission of SARS-CoV-2 within the study population. A major determinant of seropositivity has been the time interval between waves of the disease and the study period. The high seroprevalence in this study reflects the concurrent waves of the pandemic and the rising cumulative number of people exposed, with successive waves of the disease. IgM antibodies wane in the period following the wave, however IgG antibodies last for months, ranging between 6 to 18 months. The current study assessed both IgM and IgG antibodies, affording an assessment of both the recently and previously infected adolescents. Assessing

Table4. Independent predictors of SARS-CoV-2 seropositivity.

C.I: confidence interval, AOR: adjusted odd ratio, p: probability. *: p < 0.05 (Significant p-value).

both IgG and IgM potentially contributed to the higher seroprevalence observed. [17] This is made obvious when comparing the prevalence reported by Okpala etal. [18] in Anambra State, Eastern Nigeria. They reported a seroprevalence of 15.1% among adolescents, one of the lowest that has been reported among adolescents in Nigeria. Their study was done in December 2020, barely a year after the onset of the pandemic. [18] The higher prevalence in the current study is a result of the cumulative effect of multiple previous waves of infection. Kolawole [17]et al. on the other hand reported a seroprevalence of 80.5% in adolescents studied between June and August 2021. Their review coincided with the onset of the second wave of the pandemic and most studies done during the pandemic like Kolawole et al., have had a higher seroprevalence. The seropositivity in the current study represents prior infection without the bias of a surge of new infections which would no doubt create a spike in seropositivity.

At the time of this study, a small percentage of the study participants had IgM antibodies. The presence of IgM antibodies suggests ongoing (new) infections that show active transmission. Although COVID-19 preventive modes and restrictions had been relaxed in most states and even countries worldwide, we found that there was still significant ongoing transmission during the study period. The presence of active transmission in any community comes with the attendant risk of infection and re-infection in the populace. Okpala and co-workers [18] reported similar evidence of acute infection among their study population six months after the first wave of COVID-19. In both Okpala’s study and the present study, there is comparable duration after a major wave of the disease, accounting for the similarity in findings. With the resolution of a wave of disease, the fear of the spread of infection begins to resolve and both general and individual personal protective measures begin to relax. Background pockets of transmission are the facilitators of new waves of the disease. The presence of ongoing local transmission increases the risk for new waves of the disease and puts the population at risk. [19]

We identified an association between the age category of the study participants and seropositivity. Participants in their late adolescence had a higher seroprevalence than those in the early and middle adolescent age group. With advancing age, adolescents are more likely to engage in risk-taking and have less parental control. [20] They are more exposed to the outdoors and crowded environments, and this accounts for the higher prevalence observed in the older adolescent age group. Adolescents in the older age groups are more likely to interact not just with themselves within the school environment but also with other adolescents in the community, as compared with those in the early adolescent age group who are still under close control from parents/guardians and may be more restricted. The findings in this study are in keeping with the cumulative UNICEF age-disaggregated data that showed a higher number of COVID-19 cases among late adolescents than early adolescents. [3] Kolawole et al. also reported similar findings, their highest prevalence was in those aged 15 - 19 years. [17] Audu et al. in Gombe State also reported a higher prevalence in adolescents aged 15 - 19 years, when compared to those aged 10 - 14 years. [21]

In the current study, there was no association between gender and seropositivity. This is because both male and female adolescents are exposed to the same environment. Kolawole, Okpala, and Olaleye had similar findings. [17][18][22] Our findings are similar to global reports that sex does not significantly influence SARS-CoV-2 seropositivity and transmissibility. The World Health Organization and the African Centre for Disease Control indicated that gender has no role in SARS-CoV-2 seropositivity.

We found no statistically significant difference in seropositivity concerning different nutritional status. Few studies have assessed the relationship between seropositivity and nutritional status. Nwosu et al in their study noted higher seroprevalence in obese individuals. [23] Studies have suggested that a positive correlation between obesity and seropositivity may be related to severe illness, which is more common in obese individuals and linked to longer-lasting antibody responses. [23] These findings are further buttressed by Karachaliou et al in Spain who demonstrated that obese people had higher positive responses. [24] However, after adjustments were made for the severity of infection, associations were largely diluted. Although Karachaliou et al. noted higher seroprevalence among obese individuals, the current study did not have any obese participants and did not observe any relationship between seropositivity and nutritional status. Most of the study participants had normal stature with only a few being overweight or thin. This might account for the lack of significant difference as most of the study population clustered within the normal BMI group.

In the present study, participants in the lower socioeconomic class had higher seropositivity than those in the higher and middle classes. This finding was also reported by Indenbaum in Israel, and Ferreira in Brazil. [25][26] The higher seropositivity in adolescents of lower socioeconomic class may be linked to higher attendance at public schools by these adolescents. These public schools are often overcrowded, a factor that was noted to independently predict seropositivity in this study. The pattern of housing in overcrowded suburban regions occupied by those in the lower socioeconomic classes may also be a factor. Overcrowding increases the likelihood of transmission via respiratory droplets. Of note was that overcrowding in schools with other students from different homes was even more of a contributor than overcrowding at home with members of the same family. Also, adolescents from the lower socioeconomic class may have limited ability to acquire personal protective materials hence increasing the chances of transmission among them. The role of social distancing and the use of personal protective material in the prevention of SARS-CoV-2 transmission have been alluded to in previous studies.

Despite the low reports of COVID-19 in Nigeria, there is a high seroprevalence of SARS-CoV-2 antibodies among adolescents in Benin City. Adolescents in overcrowded classrooms, older adolescents and those from lower socio-economic classes are more likely to be seropositive. Transmission remains ongoing among the adolescent population who may serve as the source of the infection for their vulnerable parents and other elderly persons in their homes.

There is a need to review the Nigerian COVID-19 immunization policy to include adolescents. Clinicians should maintain a high index of suspicion and include testing for SARS-CoV-2 in adolescents who present with respiratory illness and symptoms simulating post-COVID sequelae.

There should be continued public protective measures to mitigate the spread of the infection and reduce ongoing transmission.

The recommended student: Teacher ratio for classrooms of 1 teacher to 35 students, should be maintained to avoid overcrowded school settings that could set the stage for the spread of infection.

Similar studies should be replicated in a multi-site research to generate representative national data. In addition, more studies should be carried out on the impact of nutrition on SARS-CoV-2 Seropositivity.

This study was conducted when nations had lifted COVID-19 restrictions, and most communities had relaxed most preventive measures, which could impact the outcome of the study.

IAE—conceptualization of the study and study design, data collection and entry, sample collection and analysis, interpretation of data, writing of draft and final approval of the version to be published.

AES—conceptualization and review of study design, interpretation of data, revision of draft critically for important intellectual content; and final approval of the version to be published.

EUE—conceptualization and study design, data collection and entry, sample collection and analysis, interpretation of data, revision of draft critically for important intellectual content and final approval of the version to be published.

POA—revision of the draft critically for important intellectual content; and final approval of the version to be published

All authors read and approved the final manuscript.

This study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. The research was reviewed and approved by the University of Benin Teaching Hospital Ethics Health and Research Committee (protocol number: ADM/E22/A/VOL.1457). (Appendix I) Signed informed consent was obtained from caregivers of the study participants after the purpose of the study was explained to them and participation was voluntary.

The research was self-funded by the authors and no funding was received from any funding body or organization.

The authors would like to thank Dr. P.E. Ikhurionan for his contributions to statistical analysis and proofreading of this work. Special thanks to Mr. Igbarumah, for his assistance with the University Virological research lab. We would also like to acknowledge Dr. C. Solomon for her assistance with data collection.