Mapping SARS-CoV-2 Immune Responses: A Nationwide Seroprevalence Analysis of 190,358 Healthcare Workers and General Population in Morocco (2020–2023)

Background: The COVID-19 pandemic has significantly impacted global healthcare systems, placing healthcare workers (HCWs) at heightened risk of SARS-CoV-2 exposure due to their frontline roles. Objective: The purpose of this study is to assess and compare IgG antibody prevalence against SARS-CoV-2 among healthcare workers (HCWs) and the general population (GP) in Morocco from 2020 to 2023. It investigates seroprevalence trends across pre- and post-vaccination phases to deepen understanding of immune responses and inform evidence-based public health strategies. Methodology: A prospective cohort study spanned 2020–2023 across twelve Moroccan regions, assessing IgG antibody prevalence. Serological testing was conducted pre- and post-vaccination, with adjusted seroprevalence rates calculated to account for demographic and clinical factors. Results: A nationwide seroprevalence study was conducted with 190,358 participants, including 25,452 healthcare workers (HCWs) and 164,906 general population (GP) individuals. In the pre-vaccination phase, serological testing of 110,699 participants identified 24,770 seropositive, 82,466 seronegative, and 3,463 inconclusive cases, resulting in an adjusted seroprevalence of 24.7% (95% CI: [24,4%;25%]). HCWs demonstrated a significantly higher seroprevalence (30.8%; CI: [30,5%;31,1%]) compared to the GP (22.7%;95% CI:[22,4%;23,0%]), with an odds ratio of 1.28 (95% CI: [1,23;1,33], p<0.05), indicating elevated occupational exposure risk. Post-vaccination testing of 79,659 participants revealed an overall seroprevalence of 96.8% (95%CI: [96,7%;96,9%]), with 97.8% (95% CI [97,7%;97,9%]) for HCWs and 96.7% (95% CI [96,7%;96,9%]) for the GP. Multivariable analysis indicated that HCW status did not significantly influence seropositivity after vaccination (p>0.05). It highlighted vaccination status, prior SARS-CoV-2 infection, and age as the key determinants of seropositivity in the post-vaccination period. Conclusions: Before vaccination, healthcare workers (HCWs) showed a significantly higher IgG seroprevalence compared to the general population (GP), indicating greater occupational exposure. After vaccination, nearly universal seroprevalence in both groups underscores the success of the vaccination campaign in establishing widespread immunity.