Spatial Clustering of Vaccine Exemptions on the Risk of a Measles Outbreak

OBJECTIVES Areas of increased school-entry vaccination exemptions play a key role in epidemics of vaccine-preventable diseases in the United States. California eliminated nonmedical exemptions in 2016, which increased overall vaccine coverage but also rates of medical exemptions. We examine how spatial clustering of exemptions contributed to measles outbreak potential pre- and postpolicy change. METHODS We modeled measles transmission in an empirically calibrated hypothetical population of youth aged 0 to 17 years in California and compared outbreak sizes under the observed spatial clustering of exemptions in schools pre- and postpolicy change with counterfactual scenarios of no postpolicy change increase in medical exemptions, no clustering of exemptions, and lower population immunization levels. RESULTS The elimination of nonmedical exemptions significantly reduced both average and maximal outbreak sizes, although increases in medical exemptions resulted in more than twice as many infections, on average, than if medical exemptions were maintained at prepolicy change levels. Spatial clustering of nonmedical exemptions provided some initial protection against random introduction of measles infections; however, it ultimately allowed outbreaks with thousands more infections than when exemptions were randomly distributed. The large-scale outbreaks produced by exemption clusters could not be reproduced when exemptions were distributed randomly until population vaccination was lowered by >6 percentage points. CONCLUSIONS Despite the high overall vaccinate rate, the spatial clustering of exemptions in schools was sufficient to threaten local herd immunity and reduce protection from measles outbreaks. Policies strengthening vaccine requirements may be less effective if alternative forms of exemptions (eg, medical) are concentrated in existing low-immunization areas.

Population-based seroprevalence of SARS-CoV-2 and the herd immunity threshold in Maranhão

OBJECTIVE: To estimate the seroprevalence of SARS-CoV-2 in the state of Maranhão, Brazil. METHODS: A population-based household survey was performed, from July 27, 2020 to August 8, 2020. The estimates considered clustering, stratification and non-response. Qualitative detection of IgM and IgG antibodies was performed in a fully-automated Elecsys® Anti-SARS-CoV-2 electrochemiluminescence immunoassay on the Cobas® e601 analyzer (Roche Diagnostics). RESULTS: In total, 3,156 individuals were interviewed. Seroprevalence of total antibodies against SARS-CoV-2 was 40.4% (95%CI 35.6-45.3). Population adherence to non-pharmaceutical interventions was higher at the beginning of the pandemic than in the last month. SARS-CoV-2 infection rates were significantly lower among mask wearers and among those who maintained social and physical distancing in the last month compared to their counterparts. Among the infected, 26.0% were asymptomatic. The infection fatality rate (IFR) was 0.14%, higher for men and older adults. The IFR based on excess deaths was 0.28%. The ratio of estimated infections to reported cases was 22.2. CONCLUSIONS: To the best of our knowledge, the seroprevalence of SARS-CoV-2 estimated in this population-based survey is one of the highest reported. The local herd immunity threshold may have been reached or might be reached soon.

Genetic structure of the Chernivtsi local stock of rainbow trout (Oncorhynchus mykiss) as determined by SSR-markers

Aim. The trend towards the development of high-tech trout farms is observed in Ukraine. The analysis of the genetic structure of rainbow trout by molecular genetic methods is necessary for breeding work. Therefore, the purpose of the study was to study polymorphism at the microsatellite loci of Oncorhynchus mykis of the chernivetsk local herd. Me-thods. The determination of the genetic polymorphism was carried out according to indicators: the effective number of alleles on the locus (ne), the observed (Но) and expected (Hе) heterozygosity, indexes of fixation (Fis) and polymorphism (PIC). Results. Specific features of the structure of the gene pool of the local herd O. mykiss by the SSR loci OMM 1032, 1077, 1088, STR 15, 60, 73 were revealed. The average value of the effective number of alleles per locus was 3.87. The high average values of the heterozygosity of the local herd and the index of fixation were fixed (mean values of H e and F is: 0.73 and -0.14, respectively). А high index of polymorphism was recorded for all used DNA markers and was 0.69. Тhe possibility to analyse the genetic structure of salmon using these SSR-markers was substantiated. Conclusions. An analysis of the genetic structure of trout (O. mykiss) was performed by using of 6 microsatellite. It was shown that the investigated local herd has a high level of heterozygosity. The conducted studies have shown the effectiveness of using selected loci for individual identification and population-genetic analysis. Keywords: Oncorhynchus mykis, SSR-markers, heterozygotes, polymorphism.

Big Bulls in the Local Herd

This chapter examines the role of superintendents in local school desegregation efforts, focusing particularly on the stories of Julian Prince, Clyde Muse, Tom Dulin, and Harold Kelly, who between them led seven school districts through school desegregation. Their stories demonstrate the many challenges school leaders faced in trying to mitigate the daily operations of school desegregation. Even after the Alexander v. Holmes ruling in October 1969, which called for an immediate end to segregated schooling, many superintendents with their school boards continued to wage a fierce battle with the Department of Health, Education and Welfare over their desegregation plans. Ultimately, regardless of how they went about desegregating their schools, the superintendent as the educational leader of his school district was expected to direct and lead his school through the turmoil of school desegregation.

Population viscosity suppresses disease emergence by preserving local herd immunity

Animal reservoirs for infectious diseases pose ongoing risks to human populations. In this theory of zoonoses, the introduction event that starts an epidemic is assumed to be independent of all preceding events. However, introductions are often concentrated in communities that bridge the ecological interfaces between reservoirs and the general population. In this paper, we explore how the risks of disease emergence are altered by the aggregation of introduction events within bridge communities. In viscous bridge communities, repeated introductions can elevate the local prevalence of immunity. This local herd immunity can form a barrier reducing the opportunities for disease emergence. In some situations, reducing exposure rates counterintuitively increases the emergence hazards because of off-setting reductions in local immunity. Increases in population mixing can also increase emergence hazards, even when average contact rates are conserved. Our theory of bridge communities may help guide prevention and explain historical emergence events, where disruption of stable economic, political or demographic processes reduced population viscosity at ecological interfaces.

Wolf, Canis lupus, Avoidance Behaviour of American Elk, Cervus elaphus, in Jasper National Park, Alberta

An American Elk calf (Cervus elaphus) that was captured near human habitation in Jasper National Park, Alberta, was fitted with a radio-collar and released 40 km away in the park's main valley of the Athabasca River. The calf joined a local herd of elk, and its radio signal revealed that the elk, in two months' time, travelled eight times back and forth between the herd's traditional semi-open winter range at Devona and a largely wooded area at Rocky River >3 km away. Each time, on their trans-valley route the elk crossed a busy highway, a railway, and a partly frozen river. Sightings of elk and Wolves (Canis lupus) were inversely correlated on 97 days of observation at Devona. We conclude that the elk's migrations were prompted by their urge to avoid and flee from Wolves, which were common at both locations.