Exposure of 4-year to 24-year olds to tobacco imagery on prime-time Chilean television.

INTRODUCTION: The extent of the population's exposure to tobacco imagery across all genres of regular TV programming and the contribution of each of these genres is unknown, except for UK broadcast channels. The objective of this study is to estimate the exposure of young people to tobacco imagery on Chilean prime-time television and the programme source contributing to such exposure. METHODS: Programmes aired during 3 weeks in 2019 from the 15 highest audience channels in Chile were content-analysed for the occurrence of tobacco categorised as actual use, implied use, tobacco paraphernalia, tobacco brand appearances and whether they violated Chilean smoke-free law for each 1 min interval (92 639). The exposure of young people to tobacco content was estimated using media viewership figures. RESULTS: Young people received 29, 11 and 4 million tobacco impressions of any type, explicit use and smoke-free violation, respectively, at a rate of 21.8, 8.0 and 2.1 thousand impressions per hour of TV viewing. The main sources of exposure to tobacco impressions were feature films and animated productions, which were almost entirely non-Chilean. Finally, young people were exposed to tobacco brand impressions primarily through films, effectively circumventing the advertising ban in Chile. DISCUSSION: Television programming is a source of significant youth exposure to tobacco imagery, including branding impressions. To conform to the WHO FCTC, Chile should prohibit tobacco branding in any TV programme and require strong anti-tobacco advertisements prior to any TV programme portraying tobacco.

Seroprevalence, spatial distribution, and social determinants of SARS-CoV-2 in three urban centers of Chile.

BACKGROUND: Seroprevalence studies provide an accurate measure of SARS-CoV-2 spread and the presence of asymptomatic cases. They also provide information on the uneven impact of the pandemic, pointing out vulnerable groups to prioritize which is particularly relevant in unequal societies. However, due to their high cost, they provide limited evidence of spatial spread of the pandemic specially in unequal societies. Our objective was to estimate the prevalence of SARS-CoV-2 antibodies in Chile and model its spatial risk distribution. METHODS: During Oct-Nov 2020, we conducted a population-based serosurvey in Santiago, Talca, and Coquimbo-La Serena (2493 individuals). We explored the individual association between positive results and socio-economic and health-related variables by logistic regression for complex surveys. Then, using an Empirical Bayesian Kriging model, we estimated the infection risk spatial distribution using individual and census information, and compared these results with official records. RESULTS: Seroprevalence was 10.4% (95% CI 7.8-13.7%), ranging from 2% (Talca) to 11% (Santiago), almost three times the number officially reported. Approximately 36% of these were asymptomatic, reaching 82% below 15 years old. Seroprevalence was associated with the city of residence, previous COVID-19 diagnosis, contact with confirmed cases (especially at household), and foreign nationality. The spatial model accurately interpolated the distribution of disease risk within the cities finding significant differences in the predicted probabilities of SARS-CoV-2 infection by census zone (IQR 2.5-15.0%), related to population density and education. CONCLUSIONS: Our results underscore the transmission heterogeneity of SARS-CoV-2 within and across three urban centers of Chile. Socio-economic factors and the outcomes of this seroprevalence study enable us to identify priority areas for intervention. Our methodological approach and results can help guide the design of interdisciplinary strategies for urban contexts, not only for SARS-CoV-2 but also for other communicable diseases.

[Description of the operation of a home hospitalization unit in a public hospital at Santiago, Chile]. / Hospitalización domiciliaria: aspectos conceptuales y su aplicación en el Hospital Padre Hurtado, Santiago de Chile. Descripción de funcionamiento y su rol durante la primera ola de la pandemia COVID-19.

This article briefly discloses what home hospitalization consists of, its different models of care, and the benefits and difficulties associated with it. We also describe the operation of the home hospitalization unit of the Padre Hurtado Hospital in Santiago de Chile and the role it took in the context of the first wave of the COVID-19 Pandemic, specifically between March and August of the year 2020. We aim to share our experience with this emerging form of hospitalization that is already working in Chilean public hospitals. We also hope that this hospitalization modality will continue to grow over the years.

Longitudinal assessment of SARS-CoV-2 IgG seroconversionamong front-line healthcare workers during the first wave of the Covid-19 pandemic at a tertiary-care hospital in Chile.

BACKGROUND: Healthcare workers (HCWs) are at high risk of exposure to SARS-CoV-2. Cross-sectional studies have provided variable rates of seroprevalence in HCWs. Longitudinal assessments of the serological response to Covid-19 among HCWs are crucial to understanding the risk of infection and changes in antibody titers over time. We aimed to investigate seroprevalence and risk factors associated with seroconversion in a prospective cohort of HCWs during the peak of the first wave of the Covid-19 pandemic. METHODS: We conducted a longitudinal study among 446 front-line HCWsin a tertiary-care hospital in Chile from April to July 2020. IgG was determined monthly using two different ELISAs in serum samples of HCWs, during the three-month period. In each visit, demographic data, symptoms, risk factors, and exposure risks were also assessed. RESULTS: The overall seroprevalence at the end of the study period was 24% (95% CI20.2-28.3), with 43% of seropositive HCWs reporting no prior symptoms. Seroconversion rates significantly differed over the study period, from 2.1% to as high as 8.8% at the peak of the epidemic. There were no statistically significant differences observed between HCWs in direct clinical care of patients with Covid-19 and those working in low risk areas. Antibody titers appeared to wane over time. CONCLUSIONS: HCWs were severely affected with a high rate of seroconversion that appeared to mirror the local epidemiological situation. A significant amount of participants underwent an asymptomatic infection, highlighting the need for improved surveillance policies. Antibody titers appear to wane over time; further studies to understand this finding's impact on the risk of reinfection are warranted.

Modelling cost-effectiveness of syphilis detection strategies in prisoners: exploratory exercise in a Chilean male prison.

BACKGROUND: Syphilis, together with other sexually transmitted infections, remains a global public health problem that is far from controlled. People deprived of liberty are a vulnerable population. Control activities in prisons rely mostly on passive case detection, despite the existence of affordable alternatives that would allow switching to active case-finding strategies. Our objective was to develop a mathematical modelling framework for cost-effectiveness evaluation, from a health system perspective, of different approaches using rapid tests for the detection of syphilis in inmates' populations and to explore the results based on a Chilean male prison population. METHODS: A compartmental model was developed to characterize the transmission dynamics of syphilis inside a prison with the ongoing strategy (passive case detection, with VRDL + FTA-ABS), considering the entrance and exit of inmates over a 40 year period. The model allows simulation of the implementation of a reverse algorithm for the current situation (rapid test + VDRL), different screening strategies (entry point, massive periodically; both with rapid test + VDRL) and treatment of detected cases. The parameters for the exploratory exercise were obtained from systematic searches of indexed and grey literature and field work (EQ-5D questionnaire application and key actors interviews). Probabilistic sensitivity analysis was conducted to account for uncertainty in relevant parameters. RESULTS: The proposed framework allows the evaluation of different detection strategies. In this study, all the strategies were cost-effective in the baseline scenario when considering an ICER threshold of 1 Chilean GDP per capita (US$15,000). The strategies most likely to be cost-effective (over 80% probability) were: current situation with reverse algorithm, entry point screening and mass screening every two years; the latter was the most effective, achieving the lowest prevalence (0.7% and 1.7% over the period versus the 3% prevalence in the current situation). CONCLUSIONS: Mathematical modelling that considers the performance of different tests and detection strategies could be a useful tool for decision making. The exploratory results show the efficiency of adopting both the use of the rapid tests and performing active case detection to significantly reduce the burden of syphilis in Chilean prisons in the near future.

Compliance with the smoking ban in enclosed, semiopen and open areas of workplaces and public places in Chile.

OBJECTIVE: To assess the national level of compliance with the Chilean comprehensive smoke-free legislation by observing healthcare facilities, education centres, government offices, hospitality venues and private workplaces, by type of area within workplaces and public places: enclosed, semiopen and open. METHODOLOGY: In this cross-sectional observational study, we studied a national representative sample of 3253 venues obtained through a two-stage cluster sampling design. First, 57 municipalities were randomly selected, proportionally to the total number of venues of interest. Second, within each selected municipality, a maximum of 12 venues of each sector was selected systematically from a list of existing sites. We determined the non-compliance level by estimating the percentage of the visited venues where smoking was observed or suspected in banned areas of the premises. RESULTS: Smoking or suspicion thereof was not observed in any enclosed area of any establishment. However, smoking violations were observed in semiopen areas ranging from less than 0.5% of schools and healthcare centres to around 10% of hospitality venues or 23.0% of higher education centres. Smoking violations were also observed in outdoor areas of 6.7% and 1.6% of the health centres and schools, respectively. DISCUSSION: The stark contrast in compliance with the smoking ban between the enclosed areas and the semiopen areas may be a consequence of the complex definition of semiopen areas in the regulations. The study also reflects the need to improve the overall enforcement of the smoke-free law, particularly in universities and hospitality venues.

[Worsening situation of tuberculosis in Chile]. / El deterioro de la tuberculosis en Chile.

BACKGROUND: Recent data suggest an increase in tuberculosis (TB) incidence in Chile. AIM: To evaluate recent epidemiological trends, geographic extension and potential factors associated with TB reemergence in Chile. MATERIAL AND METHODS: Data analysis from official sources and trend analysis. RESULTS: TB incidence rate increased from 12.3 (2014) to 14.7 (2017) per 100,000 inhabitants. Morbidity rates also increased in nine out of 15 regions. The proportion of TB cases in specific groups has also increased in the last six years: HIV/AIDS (68%), immigrants (118%), drug users/alcoholics (267%) and homeless people (370%). Several indicators of the national TB program performance have deteriorated including TB case detection, HIV co-infection study and contact tracing activities. Overall results indicate a higher than expected case-fatality ratio (> 3%), high rates of loss from follow-up (> 5%), and low percentage of cohort healing rate (< 90%). This decline is associated with a Control Program with scarce human resources whose central budget decreased by 90% from 2008 to 2014. New molecular diagnostic tools and liquid media culture were only recently implemented. CONCLUSIONS: TB trends and overall program performance indicators have deteriorated in recent years in Chile and several factors appear to be involved. Multiple strategies will be required to rectify this situation.

Case-Control Study of Risk Factors for Meningococcal Disease in Chile.

An outbreak of meningococcal disease with a case-fatality rate of 30% and caused by predominantly serogroup W of Neisseria meningitidis began in Chile in 2012. This outbreak required a case-control study to assess determinants and risk factors for infection. We identified confirmed cases during January 2012-March 2013 and selected controls by random sampling of the population, matched for age and sex, resulting in 135 case-patients and 618 controls. Sociodemographic variables, habits, and previous illnesses were studied. Analyses yielded adjusted odds ratios as estimators of the probability of disease development. Results indicated that conditions of social vulnerability, such as low income and overcrowding, as well as familial history of this disease and clinical histories, especially chronic diseases and hospitalization for respiratory conditions, increased the probability of illness. Findings should contribute to direction of intersectoral public policies toward a highly vulnerable social group to enable them to improve their living conditions and health.

Correlates of compliance with national comprehensive smoke-free laws.

OBJECTIVE: To explore correlates of high compliance with smoking bans in a cross-sectional data set from the 41 countries with national comprehensive smoke-free laws in 2014 and complete data on compliance and enforcement. METHODS: Outcome variable: compliance with a national comprehensive smoke-free law in each country was obtained for 2014 from the WHO global report on the global tobacco epidemic. Explanatory variables: legal enforcement requirements, penalties, infrastructure and strategy were obtained through a separate survey of governments. Also, country socioeconomic and demographic characteristics including the level of corruption control were included. ANALYSIS: an initial bivariate analysis determined the significance of each potentially relevant explanatory variable of high compliance. Differences in compliance were tested using the exact logistic regression. RESULTS: High compliance with the national comprehensive smoke-free law was associated with the involvement of the local jurisdictions in providing training and/or guidance for inspections (OR=10.3, 95% CI 1.7 to 117.7) and a perception of high corruption control efforts in the country (OR=7.2, 95% CI 1.1 to 85.8). DISCUSSION: The results show the importance of the depth of the enforcement infrastructure and effort represented by the degree to which the local government is involved in enforcement. They also show the significance of fighting corruption in the enforcement process, including the attempts of the tobacco industry to undermine the process, to achieve high levels of compliance with the law. The results point out to the need to invest minimal but essential enforcement resources given that national comprehensive smoke-free laws are self-enforcing in many but not all countries and sectors.

Tropical high-altitude Andean lakes located above the tree line attenuate UV-A radiation more strongly than typical temperate alpine lakes.

Tropical high-altitude Andean lakes are physically harsh ecosystems. Located above the treeline (≥4000 m a.s.l.), they share common features with temperate alpine lakes, which impose extreme conditions on their aquatic organisms: e.g., strong winds, broad diel variations in water temperature, and intense solar ultraviolet radiation (UVR). However, because of their latitude, they differ in two major ecological characteristics: they lack ice cover during the winter and they do not present summer water column stratification. We sampled 26 tropical high-altitude Andean lakes from three regions of the Bolivian Eastern Andes Cordillera during the wet period (austral summer). We performed an ordination to better describe the typology of Andean lakes in relation to the environmental variables, and we assessed the relationships among them, focussing on the UV-A transparency (360 nm) throughout the water column. We found a positive correlation between UV-A transparency calculated as Z(1%) (the depth which reaches 1% of the surface UV-A), the lake maximum depth and Secchi transparency (r = 0.61). Z(1%) of UV-A was smaller in shallow lakes than in deep lakes, indicating that shallow lakes are less transparent to UV-A than deep lakes. We hypothesize that, compared to shallow lakes, deep lakes (maximum depth > 10 m) may have lower dissolved organic carbon (DOC) concentrations (that absorb UV radiation) due to lower temperature and reduced macrophyte cover. Based on our data, tropical high-altitude Andean lakes are less transparent to UV-A (K(d) range = 1.4-11.0 m(-1); Z(1%) depth range = 0.4-3.2 m) than typical temperate alpine lakes (1-6 m(-1), 3-45 m, respectively). Moreover, they differ in vertical profiles of UV-A, chlorophyll-a, and temperature, suggesting that they may have a distinct ecological functioning. Such peculiarities justify treating tropical high-altitude Andean lakes as a separate category of alpine lakes. Tropical high-altitude Andean lakes have been poorly studied. Thus they deserve more in-depth studies in the face of global changes regarding the use of their UV transparency as a sentinel proxy of climate changes, particularly global warming.

[Barriers and facilitators to antenatal care in adolescents: results of a qualitative study in Chile]. / Barreras y facilitadores para el control prenatal en adolescentes: resultados de un estudio cualitativo en Chile.

OBJECTIVE: Analyze barriers and facilitators of access to prenatal care in pregnant urban adolescents between 15-19 years of age in Santiago, Chile. MATERIALS AND METHODS: Qualitative study based on grounded theory with 17 adolescent mothers. Eleven semi-structured interviews and one focus group were conducted. RESULT: . The denial and concealment of pregnancy is the main barrier to start the prenatal care in the "delayed access group". This group does not identify facilitators. For maintenance in antenatal care, all participants identified a support figure as a facilitator. Family and social vulnerabilities explain why some adolescents start the prenatal care late. CONCLUSION: The presence of facilitators is crucial for both, the timely entry and the maintenance in antenatal care because they reduce or nullify the effect of barriers. The health system must become a facilitator to accompany adolescents and promote a bond of trust and respect.

Seroprevalence of Natural and Acquired Immunity against the SARS-CoV-2 Virus in a Population Cohort from Two Chilean Cities, 2020-2022.

BACKGROUND: Chile has achieved the highest coverage for vaccines against the SARS-CoV-2 virus worldwide. OBJECTIVE: To assess the progression of immunity (natural and acquired by vaccine) in a cohort from two Chilean cities. METHODS: Individuals (n = 386) who participated in three phases of population-based serial prevalence studies were included (2020-2021 and 2022). Presence of SARS-CoV-2 antibodies was measured in serum. Data including time of vaccination and type of vaccine received were analysed with descriptive statistics. RESULTS: Seroprevalence was 3.6% in the first round and increased to 96.9% in the second and 98.7% in the third. In the third round, 75% of individuals who had received the basal full scheme were seropositive at 180 days or more since their last dose; 98% of individuals who received one booster dose were seropositive at 180 days or more, and 100% participants who received two boosters were seropositive, regardless of time since their last dose. Participants receiving mRNA vaccines had higher seroprevalence rates over time. CONCLUSIONS: The high vaccination coverage in Chile enabled the population to maintain high levels of antibodies. Vaccination boosters are essential to maintain immunity over time, which also depends on the type of vaccine administered.

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.

The 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.

Exposure to tobacco impressions during prime-time TV among Chilean minors by sex and socioeconomic status.

INTRODUCTION: We tested if tobacco impressions were delivered differentially to prime-time TV watching minors by sex and socioeconomic status. METHODS: Programs aired during prime-time for three random weeks in 2019 from the 15 highest audience channels in Chile were content-analyzed for the occurrence of tobacco for each one-minute interval of 92639 recorded. Such occurrences were categorized as actual use and whether they violated Chilean smoke-free law or tobacco brand appearances. We estimated the number of persons per hour (p/h) exposed to tobacco impressions for the 4 to 17 years age group by sex and socioeconomic status (SES). RESULTS: Minors spent over a billion p/h watching TV during the observation period. Minors were exposed to tobacco explicit use, branding and smoke-free violation impressions for 9.7 million, 1.2 million, and 1.0 million p/h, respectively. The odds ratios (OR) of exposure to total tobacco impressions were always greater among boys with higher SES compared to boys with low SES. However, they were greater among girls of low SES compared to those of high SES for all types of impressions. The OR of exposure to tobacco branding was higher among girls of any SES compared to boys of any SES. CONCLUSIONS: Minors need protection from tobacco imagery on television, particularly girls of low SES. To that end, new legislation should implement all measures to counter depictions of tobacco in entertainment media, as recommended in the WHO FCTC Article 13 guidelines. This should require strong anti-tobacco advertisements before any TV program portraying tobacco targeting minor audiences, particularly girls of low SES. Given that Chile has one of the highest prevalences in the world of current cigarette smoking among young females, the potential contribution of tobacco impressions on TV to smoking differentials across female socioeconomic groups should be further studied.

Seroprevalence and estimation of the impact of SARS-CoV-2 infection in older adults residing in Long-term Care Facilities in Chile. / Seroprevalencia y estimación del impacto de la infección por SARS-CoV-2 en personas mayores residentes en centros de larga estadía en Chile.

Introduction: Older adults are at a higher risk of severe illness and death from COVID-19. This vulnerability increases in those who live in long-term care facilities due to overcrowding, greater physical dependence, and contact with health workers. Evidence on the impact of the pandemic on these establishments in lowand middle-income countries has been scant. This study aims to determine the seroprevalence of SARS-CoV-2 in older people residing in long-term care facilities and estimate the impact of infection after the first wave of the pandemic. Methods: A cross-sectional design with 2099 residents in three regions of Chile was carried out between September and November 2020. Measurement of antibodies was performed with a rapid test. The impact of SARS-CoV-2 infection was estimated with seropositive residents, those who had a history of positive polymerase chain reaction tests, and those who died from COVID-19. Bivariate analysis with the region, sex, age, history of COVID-19, physical dependence, and serological results were performed. In addition, we performed a correlation analysis between the seroprevalence of the centers by the municipality and the rate of confirmed cases. Results: The seroprevalence of SARS-CoV-2 antibodies in the three regions was 14.7% (95% confidence interval: 13.2 to 16.3%), the infection impact was 46.4%, and the fatality rate was 19.6%. A significant correlation was found between the seroprevalence of older adults residing in long-term care facilities and the cumulative incidence by municipalities. Conclusions: The seroprevalence of older adults residing in long-term care facilities was higher than the general population. The high impact of infection among this population at the end of the first wave of the COVID-19 pandemic is similar to other countries. The centers' environment is directly related to COVID-19 infection. Morbidity and mortality monitoring systems should be implemented promptly to establish prevention and control measures.

Introducción: Las personas mayores tienen más riesgo de enfermar gravemente y fallecer por COVID-19. Esta vulnerabilidad aumenta en quienes viven en establecimientos de larga estadía, debido a hacinamiento, mayor dependencia física y contacto con los trabajadores. La evidencia sobre el impacto de la pandemia de estos establecimientos en países de medianos y bajos ingresos ha sido escasa. El objetivo es determinar la seroprevalencia de la infección por SARS-CoV-2 en personas mayores que residen en establecimientos de larga estadía. Así como estimar el impacto global de la infección después de la primera ola de la pandemia. Métodos: Diseño transversal con 2099 residentes en tres regiones de Chile, realizado entre septiembre y noviembre 2020. Anticuerpos fueron medidos con test rápido contra SARS-CoV-2. Se estimó el impacto de la infección con los residentes seropositivos, los residentes con antecedentes de reacción en cadena de la polimerasa de transcripción inversa positiva, y residentes que murieron por COVID-19. Análisis bivariado entre el resultado serológico y región, sexo, edad, antecedentes de COVID-19 y dependencia física fueron realizados. Además, realizamos un análisis de correlación entre la seroprevalencia de los centros por municipio y la tasa acumulada de casos confirmados. Resultados: La seroprevalencia de anticuerpos en las tres regiones fue 14,7% (intervalo de confianza del 95%: 13,2 a 16,3%). El impacto real de la infección se estimó en 46,4% y la tasa de letalidad en 19,6%. La seroprevalencia de los residentes de los centros por comuna se correlacionó positiva y significativamente con la frecuencia de la enfermedad a nivel comunal. Conclusiones: Seroprevalencia superior a la de la población general, observándose un alto impacto de la infección por COVID-19 al final de la primera ola de la pandemia. El lugar en el que se encuentran los establecimientos está directamente relacionado con la tasa de seroprevalencia en ellos. Sistemas de vigilancia epidemiológica deben aplicarse con prontitud para establecer medidas de prevención y control.

First wave of SARS-CoV-2 in Santiago Chile: Seroprevalence, asymptomatic infection and infection fatality rate.

BACKGROUND: The first wave of SARS-CoV-2 infection in Chile occurred during the cold season reaching a peak by the end of June 2020, with 80 % of the cases concentrated in its capital, Santiago. The main objective of this study was to estimate the attack rate during this first wave of SARS-CoV-2 in a large, densely populated city with more than seven million inhabitants. Since the number of confirmed cases provides biased information due to individuals' potential self-selection, mostly related to asymptomatic patients and testing access, we measured antibodies against SARS-CoV-2 to assess infection prevalence during the first wave in the city, as well as estimate asymptomatic cases, and infection fatality ratio. To our knowledge this is one of the few population-based cross-sectional serosurvey during the first wave in a highly affected emerging country. The challenges of pandemic response in urban settings in a capital city like Santiago, with heterogeneous subpopulations and high mobility through public transportation, highlight the necessity of more accurate information regarding the first waves of new emerging diseases. METHODS: From April 24 to June 21, 2020, 1326 individuals were sampled from a long-standing panel of household representatives of Santiago. Immunochromatographic assays were used to detect IgM and IgG antibody isotypes. RESULTS: Seroprevalence reached 6.79 % (95 %CI 5.58 %-8.26 %) in the first 107 days of the pandemic, without significant differences among sex and age groups; this figure indicates an attack rate 2.8 times higher than the one calculated with registered cases. It also changes the fatality rate estimates, from a 2.33 % case fatality rate reported by MOH to an estimated crude 1.00 % (CI95 % 0.97-1.03) infection fatality rate (adjusted for test performance 1.66 % [CI95 % 1.61-1.71]). Most seropositive were symptomatic (81,1 %). CONCLUSIONS: Despite the high number of cases registered, mortality rates, and the stress produced over the health system, the vast majority of the people remained susceptible to potential new epidemic waves. We contribute to the understanding of the initial spread of emerging epidemic threats. Consequently, our results provide better information to design early strategies that counterattack new health challenges in urban contexts.

Immunization and SARS-CoV-2 Antibody Seroprevalence in a Country with High Vaccination Coverage: Lessons from Chile.

Chile is among the most successful nations worldwide in terms of its COVID-19 vaccine rollout. By 31 December 2021, 84.1% of the population was fully vaccinated, and 56.1% received booster doses using different COVID-19 vaccines. In this context, we aimed to estimate the prevalence of anti-SARS-CoV-2 antibodies following the infection and vaccination campaign. Using a three-stage stratified sampling, we performed a population-based cross-sectional serosurvey based on a representative sample of three Chilean cities. Selected participants were blood-sampled on-site and answered a short COVID-19 and vaccination history questionnaire using Wantai SARS-CoV-2 Ab ELISA to determine seroprevalence. We recruited 2198 individuals aged 7-93 between 5 October and 25 November 2021; 2132 individuals received COVID-19 vaccinations (97%), 67 (3.1%) received one dose, 2065 (93.9%) received two doses, and 936 received the booster jab (42.6%). Antibody seroprevalence reached 97.3%, ranging from 40.9% among those not vaccinated to 99.8% in those with booster doses (OR = 674.6, 154.8-2938.5). SARS-CoV-2 antibodies were associated with vaccination, previous COVID-19 diagnosis, age group, and city of residence. In contrast, we found no significant differences in the type of vaccine used, education, nationality, or type of health insurance. We found a seroprevalence close to 100%, primarily due to the successful vaccination program, which strongly emphasizes universal access.

SARS-CoV-2 Neutralizing Antibodies in Chile after a Vaccination Campaign with Five Different Schemes.

Using levels of neutralizing antibodies (nAbs), we evaluate the successful Chilean SARS-CoV-2 vaccine campaign, which combines different vaccine technologies and heterologous boosters. From a population-based study performed in November 2021, we randomly selected 120 seropositive individuals, organized into six groups of positive samples (20 subjects each) according to natural infection history and the five most frequent vaccination schemes. We conclude that the booster dose, regardless of vaccine technology or natural infection, and mRNA vaccines significantly improve nAbs response.