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This study assessed the seroprevalence of SARS-CoV-2 and antibody responses in a high-risk adult population and hospitalized children in the state of Morelos. An ELISA test utilizing the SARS-CoV-2 spike protein’s RBD domain was employed to detect IgG, IgM, and IgA antibodies. Among adults, before vaccination campaigns (n = 114), 26.3 % tested positive for IgG, while IgM and IgA were detected in 19.3 % and 13.2 %, respectively. The impact of Pfizer-BioNTech (BNT162b2) vaccination was analyzed, revealing significant increases in antibody levels following the second dose. Subsequently, participants receiving third doses from different vaccines exhibited comparable or higher IgG and IgM levels. IgA levels varied, with a subset reaching high levels only after receiving the booster dose. Children, before vaccination campaigns (n = 115), displayed 56.5 % IgG seropositivity, despite minimal reported COVID-19 cases. Elevated MIS-C/Kawasaki syndrome diagnoses (15 %) prompted a need for pediatric diagnosis focus. Comparative analysis of antibodies’ levels in seropositive adults and children showed higher responses in adults both after infection (IgG: r = 0.42, p < 0.001; IgM: r = 0.63, p < 0.001) and after application of two vaccine doses (IgG: r = 0.52, p < 0.001; IgM: r = 0.57, p < 0.001; IgA: r = 0.26, p < 0.001). These findings underscore the necessity for continued antibody response monitoring post-vaccination in children and emphasize the importance of tailored vaccination strategies and diagnostic prioritization to address SARS-CoV-2 immunity in diverse populations. [ABSTRACT FROM AUTHOR]

Five of the eight vaccines approved in Mexico to be used against COVID-19 are adenovirus-based, including Gam-COVID-Vac (Sputnik V), Ad5-nCoV Covidecia, Ad26.COV2-S, and AZD1222 Covishield. AdV-based vaccines have shown promise due to their ability to induce robust B- and T-cell responses. However, studies indicate high levels of prior exposure to HAdV-C5 and neutralizing antibodies in the human population that could interfere with the efficacy of the vaccine, while the prevalence of antibodies against HAdV-D26 varies worldwide. In Mexico, data on AdV seroprevalence are scarce, hindering predictions about vaccine efficacy, immunity duration, and their use for boosters or seasonal application. In this work we have analyzed pre-COVID-19 pandemic and pre-COVID-19 vaccination blood samples from healthy Mexican adult donors for antibodies against different AdV types (from species A to F) and simian AdVs (SAdV-21, SAdV-25, and SAdV-31) using ELISA and neutralization assays. The highest levels of neutralizing antibodies were observed for HAdV-C5, HAdV-C6, HAdV-B14, and HAdV-F41, while SAdV-21, SAdV-25, and SAdV-31 showed negligible neutralization. HAdV-D36, HAdV-A12, and HAdV-E4 formed a separate cluster with intermediate neutralization levels. Notably, HAdV-D26 exhibited low neutralization, similar to developed countries. These findings show widespread and high prevalence of adenovirus in healthy individuals in Mexico, with levels that are similar to developing countries for HAdV-C5 or HAdV-F41, while more closely matching levels in developed countries for HAdV-D26. The data indicate that HAdV-D26 and SAdV21 are good vaccine vector candidates for the Mexican population due to their low prevalence. The data should contribute to plans for vaccine development and vaccination strategies by national health authorities, including seasonal vaccine application and the development of new AdV-based vaccines. [ABSTRACT FROM AUTHOR]