Exploring cell-free assays for COVID-19 serosurvey.

Serosurveys to monitor immunity toward COVID-19 in the population are primarily performed using an ELISA to screen samples for SARS-CoV-2 antibodies, followed by confirmation by a virus neutralization test, which is considered the Gold Standard. However, virus neutralization test may not be feasible for some laboratories because of the requirement for specific facilities and trained personnel. In an attempt to address this limitation, we evaluated three cell-free methods as potential alternatives for assessing SARS-CoV-2 seroprevalence in human population from plasma. We report the establishment of two inhibition ELISAs designed to detect anti-Spike RBD IgG antibodies and a microsphere quantitative suspension array technology assay, based on the Luminex xMAP platform, to measure the presence of antibodies against various SARS-CoV-2 antigens, including anti-RBD. These methods were also compared to a commercial chemiluminescent immunoassay designed for anti-RBD antibodies detection and to the combined ELISA + virus neutralization test strategy. These cell-free assays performed equally to estimate the percentage of positive and negative samples and could be used to determine the prevalence of SARS-CoV-2 antibodies in human population, at least in cohort with high-expected prevalence, without the use of seroneutralization assay.

Metapopulation dynamics of SARS-CoV-2 transmission in a small-scale Amazonian society.

The severity of infectious disease outbreaks is governed by patterns of human contact, which vary by geography, social organization, mobility, access to technology and healthcare, economic development, and culture. Whereas globalized societies and urban centers exhibit characteristics that can heighten vulnerability to pandemics, small-scale subsistence societies occupying remote, rural areas may be buffered. Accordingly, voluntary collective isolation has been proposed as one strategy to mitigate the impacts of COVID-19 and other pandemics on small-scale Indigenous populations with minimal access to healthcare infrastructure. To assess the vulnerability of such populations and the viability of interventions such as voluntary collective isolation, we simulate and analyze the dynamics of SARS-CoV-2 infection among Amazonian forager-horticulturalists in Bolivia using a stochastic network metapopulation model parameterized with high-resolution empirical data on population structure, mobility, and contact networks. Our model suggests that relative isolation offers little protection at the population level (expected approximately 80% cumulative incidence), and more remote communities are not conferred protection via greater distance from outside sources of infection, due to common features of small-scale societies that promote rapid disease transmission such as high rates of travel and dense social networks. Neighborhood density, central household location in villages, and household size greatly increase the individual risk of infection. Simulated interventions further demonstrate that without implausibly high levels of centralized control, collective isolation is unlikely to be effective, especially if it is difficult to restrict visitation between communities as well as travel to outside areas. Finally, comparison of model results to empirical COVID-19 outcomes measured via seroassay suggest that our theoretical model is successful at predicting outbreak severity at both the population and community levels. Taken together, these findings suggest that the social organization and relative isolation from urban centers of many rural Indigenous communities offer little protection from pandemics and that standard control measures, including vaccination, are required to counteract effects of tight-knit social structures characteristic of small-scale populations.

A novel and sensitive real-time PCR system for universal detection of poxviruses.

Success in smallpox eradication was enabled by the absence of non-human reservoir for smallpox virus. However, other poxviruses with a wider host spectrum can infect humans and represent a potential health threat to humans, highlighted by a progressively increasing number of infections by (re)emerging poxviruses, requiring new improved diagnostic and epidemiological tools. We describe here a real-time PCR assay targeting a highly conserved region of the poxvirus genome, thus allowing a pan-Poxvirus detection (Chordopoxvirinae and Entomopoxvirinae). This system is specific (99.8% for vertebrate samples and 99.7% for arthropods samples), sensitive (100% for vertebrate samples and 86.3% for arthropods samples) and presents low limit of detection (< 1000 DNA copies/reaction). In addition, this system could be also valuable for virus discovery and epidemiological projects.

Impact of rotavirus vaccination on child mortality, morbidity, and rotavirus-related hospitalizations in Bolivia.

BACKGROUND: The public health impact of rotavirus vaccination in countries with high child mortality rates remains to be established. The RV1 rotavirus vaccine was introduced in Bolivia in August 2008. This study describes the trends in deaths, hospitalizations, and healthcare visits due to acute gastroenteritis (AGE) and in rotavirus-related hospitalizations, among children <5 years of age, during the pre- and post-vaccination periods. METHODS: Data were obtained from the National Health Information System to calculate vaccine coverage and AGE-related health indicators. Trend reductions in the main health indicators were examined using the pre-vaccine period as baseline. The effect of vaccination on the epidemiology of rotavirus-related AGE was assessed using data from the active surveillance hospitals. RESULTS: Compared with the 2001-2008 pre-vaccine baseline, the mean number of rotavirus-related hospitalizations was reduced by 40.8% (95% confidence interval (CI) 21.7-66.4%) among children <5years of age in the post-vaccine period (2009-2013). Reductions were most pronounced in children <1year of age, eligible for vaccination. The mean proportions of AGE-related deaths, AGE-related hospitalizations, and AGE-related healthcare visits during 2009-2014 were reduced by 52.5% (95% CI 47.4-56.3), 30.2% (95% CI 23.5-36.1), and 12.9% (95% CI 12.0-13.2), respectively. The greatest effect in reduction of AGE-related deaths was found during the months with seasonal peaks of rotavirus disease. Over the post-vaccine period, changes in rotavirus epidemiology were observed, manifested by variations in seasonality and by a shift in the mean age of those with rotavirus infection. CONCLUSIONS: The significant decrease in main AGE-related health indicators in children <5years of age after the introduction of rotavirus vaccine provides evidence of a substantial public health impact of rotavirus vaccination in Bolivia, as a measure for protecting children against AGE.