Person: Aguilera, Ximena
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Publication Factors influencing neutralizing antibody response to the original SARS-CoV-2 virus and the Omicron variant in a high vaccination coverage country, a population-based study(2023) Hormazabal, Juan; Nuñez-Franz, Loreto; Rubilar, Paola; Apablaza, Mauricio; Vial Cox, María Cecilia; Cortes Salinas, Lina Jimena; González, Natalia; Vial, Pablo; Said, Macarena; Gonzalez Wiedmaier, Claudia; Olivares, Kathya; Aguilera, Ximena; Ramírez-Santana, MurielThe study compared immunity to the original SARS-CoV-2 virus (Wuhan) and the Omicron variant using neutralizing antibodies (NAbs), that provide a good approximation of protective immunity. The results might help determine immunization strategies. Design and methods: Unlike previous studies, we analyzed NAbs in a random sample of 110 IgG positive sera from individuals who participated in a population-based seroprevalence transversal study, carried out in May 2022 in two Chilean cities, a country with high vaccination coverage. Results: Our findings indicate that 98.2% of individuals had NAbs against Wuhan, 65.5% against Omicron, and 32.7% tested positive for Wuhan but not Omicron. Factors influencing protective immunity included a prior natural infection and the number of vaccines received. NAbs titers against the original virus were high, demonstrating vaccine effectiveness in the population. However, the level of antibodies decreased when measuring NAbs against Omicron, particularly among older individuals, indicating a decline in vaccine protection. Previous COVID-19 episodes acted as a natural booster, increasing NAbs titers against both virus strains. Conclusions: Protective immunity against the original Wuhan SARS-CoV-2 virus is reduced when compared to Omicron variant. Updating vaccine to target emerging variants and continued monitoring of effectiveness at the population level are necessary.Publication SARS-CoV-2 infectivity and antigenic evasion: spotlight on isolated Omicron sub-lineages(2024) Barrera, Aldo; Martínez, Constanza; Angulo, Jenniffer; Palma, Carlos; Hormazabal, Juan; Vial Cox, María Cecilia; Aguilera, Ximena; Castillo, Pablo; Pardo, Catalina; Balcells, María; Nervi, Bruno; Le Corre, Nicole; Ferrés, MarcelaSince the SARS-CoV-2 outbreak in 2019, a diversity of viral genomic variants has emerged and spread globally due to increased transmissibility, pathogenicity, and immune evasion. By the first trimester of 2023 in Chile, as in most countries, BQ and XBB were the predominant circulating sub-lineages of Omicron. The molecular and antigenic characteristics of these variants have been mainly determined using non-authentic spike pseudoviruses, which is often described as a limitation. Additionally, few comparative studies using isolates from recent Omicron sub-lineages have been conducted. In this study, we isolated SARS-CoV-2 variants from clinical samples, including the ancestral B.1.1, Delta, Omicron BA.1, and sub-lineages of BA.2 and BA.5. We assessed their infectivity through cell culture infections and their antibody evasion using neutralization assays. We observed variations in viral plaque size, cell morphology, and cytotoxicity upon infection in Vero E6-TMPRSS2 cells for each variant compared to the ancestral B.1.1 virus. BA.2-derived sub-variants, such as XBB.1.5, showed attenuated viral replication, while BA.5-derived variants, such as BQ.1.1, exhibited replication rates similar to the ancestral SARS-CoV-2 virus. Similar trends were observed in intestinal Caco-2 cells, except for Delta. Antibody neutralization experiments using sera from individuals infected during the first COVID-19 wave (FWI) showed a consistent but moderate reduction in neutralization against Omicron sub-lineages. Interestingly, despite being less prevalent, BQ.1.1 showed a 6.1-fold greater escape from neutralization than XBB.1.5. Neutralization patterns were similar when tested against sera from individuals vaccinated with 3xBNT162b2 (PPP) or Coronavac-Coronavac-BNT162b2 (CCP) schedules. However, CCP sera showed 2.3-fold higher neutralization against XBB.1.5 than FWI and PPP sera. This study provides new insights into the differences between BA.2 and BA.5-derived variants, leading to their eventual outcompetition. Our analysis offers important evidence regarding the balance between infectivity and antigenic escape that drives the evolution of second-generation SARS-CoV-2 variants in the population.Publication Overcoming Health Inequities: Spatial Analysis of Seroprevalence and Vaccination Against COVID-19 in Chile(2024) Muriel Ramírez-Santana , Juan Hormazábal, Luis Canales, Pablo Vial, and Ximena Aguilera; Correa, Juan; Núñez Franz, Loreto; Apablaza, Mauricio; Rubilar, Paola; Vial Cox, María Cecilia; Cortes, Lina Jimena; Hormazabal, Juan; Canales, Luis; Vial, Pablo; Aguilera, XimenaBackground: In unequal economies, the spread of the first waves of the COVID-19 was usually associated withlow socioeconomic status of individuals and their families. Chile exemplified this. By mid-2020, Chile had one ofthe highest SARS-CoV-2 infection rates in the world predominantly in poorer areas. A year later, the countrylaunched a universal vaccination campaign based on the national strategy of immunization established in1975. By 2022, Chile presented one of the highest COVID-19 vaccination coverages globally, reaching 94.3%of the population with the primary scheme by the end of 2022.Objective: This study analyzes the spatial distribution of SARS-CoV-2 seroprevalence at the beginning of the pan-demic (2020) compared with the seroprevalence after 2 years of ongoing epidemic and COVID-19 vaccinationcampaigns (2022).Methods: Two population-based random samples of individuals aged 7 years and older from two Chilean citieswere studied. Utilizing an enzyme-linked immunosorbent assay test, IgG antibodies were measured in serum of1061 participants in 2020, and 853 in 2022.Results: Using the Global Moran’s Index, the seroprevalence distribution pattern for the year 2020 showed clus-tering in the two cities. Conversely, seroprevalence and vaccinations were homogeneously distributed in 2022.These results show the success of the vaccination campaign in Chile, not only in coverage but also because itwidely reached all individuals.Conclusions: The uptake of this preventive measure is high, regardless of the social and economic factors,achieving broad population immunity. The extensive deployment of the primary health care network contrib-uted to reducing health inequities and promoting to universal health access.