The evolutionary cost of homophily: social stratification facilitates stable variant coexistence and increased rates of evolution in host-associated pathogens.

Coexistence of multiple strains of a pathogen in a host population can present significant challenges to vaccine development or treatment efficacy. Here we discuss a novel mechanism that can increase rates of long-lived strain polymorphism, rooted in the presence of social structure in a host population. We show that social preference of interaction, in conjunction with differences in immunity between host subgroups, can exert varying selection pressure on pathogen strains, creating a balancing mechanism that supports stable viral coexistence, independent of other known mechanisms. We use population genetic models to study rates of pathogen heterozygosity as a function of population size, host population composition, mutant strain fitness differences and host social preferences of interaction. We also show that even small periodic epochs of host population stratification can lead to elevated strain coexistence. These results are robust to varying social preferences of interaction, overall differences in strain fitnesses, and spatial heterogeneity in host population composition. Our results highlight the role of host population social stratification in increasing rates of pathogen strain diversity, with effects that should be considered when designing policies or treatments with a long-term view of curbing pathogen evolution.

Risk factors associated with cognitive impairment in patients with COVID-19: a protocol of systematic review and meta-analysis.

INTRODUCTION: COVID-19 infections have become a global public health emergency. Although COVID-19 is primarily a respiratory disease, some of hospitalised patients exhibit cognitive impairment-related neurological damage. Using a systematic review and meta-analysis, we aim to investigate the risk factors for cognitive impairment in patients with COVID-19. METHODS AND ANALYSIS: This meta-analysis has been registered with the International Prospective Register of Systematic Reviews. From inception to 5 August 2022, we will search PubMed, Web of Science, Embase via Ovid, the Chinese Biological Medical Database and the Cochrane Central Register of Controlled Trials (CENTRAL) for relevant studies . We will also look for additional studies in the reference lists of selected articles. To ensure data quality and accuracy, only researches published in English and Chinese will be included. Fixed or random-effects model will be used to calculate the relative risk (RR) or odds ratio (OR) and 95% CIs for pooled data about dichotomous outcomes. We will also assess heterogeneity using Cochrane's Q and I2 tests. Cognitive impairment RR or OR is the primary outcome. ETHICS AND DISSEMINATION: Data will be extracted from published studies, so ethical approval is not required. The outcomes of this meta-analysis will be published in a journal with peer review. PROSPERO REGISTRATION NUMBER: CRD42022351011.