Dynamic Contact Networks of Residents of an Urban Jail in the Era of SARS-CoV-2 (preprint)

BACKGROUND. In custodial settings such as jails and prisons, infectious disease transmission is heightened by factors such as overcrowding and limited healthcare access. Specific features of social contact networks within these settings have not been sufficiently characterized, especially in the context of a large-scale respiratory infectious disease outbreak. The study aims to quantify contact network dynamics within the Fulton County Jail in Atlanta, Georgia, to improve our understanding respiratory disease spread to informs public health interventions. METHODS. As part of the Surveillance by Wastewater and Nasal Self-collection of Specimens (SWANSS) study, jail roster data were utilized to construct social contact networks. Rosters included resident details, cell locations, and demographic information. This analysis involved 6,702 residents over 140,901 person days. Network statistics, including degree, mixing, and turnover rates, were assessed across age groups, race/ethnicities, and jail floors. We compared outcomes for two distinct periods (January 2022 and April 2022) to understand potential responses in network structures during and after the SARS-CoV-2 Omicron variant peak. RESULTS. We found high cross-sectional network degree at both cell and block levels, indicative of substantial daily contacts. While mean degree increased with age, older residents exhibited lower degree during the Omicron peak, suggesting potential quarantine measures. Block-level networks demonstrated higher mean degrees than cell-level networks. Cumulative degree distributions for both levels increased from January to April, indicating heightened contacts after the outbreak. Assortative age mixing was strong, especially for residents aged 20-29. Dynamic network statistics illustrated increased degrees over time, emphasizing the potential for disease spread, albeit with a lower growth rate during the Omicron peak. CONCLUSIONS. The contact networks within the Fulton County Jail presented ideal conditions for infectious disease transmission. Despite some reduction in network characteristics during the Omicron peak, the potential for disease spread remained high. Age-specific mixing patterns suggested unintentional age segregation, potentially limiting disease spread to older residents. The study underscores the need for ongoing monitoring of contact networks in carceral settings and provides valuable insights for epidemic modeling and intervention strategies, including quarantine, depopulation, and vaccination. This network analysis offers a foundation for understanding disease dynamics in carceral environments.

Can long-term COVID-19 vaccination be improved by serological surveillance?: a modeling study for Mozambique (preprint)

Seroprevalence provides an estimate of the population-level susceptibility to infection. In this study, we used a transmission model to examine the potential of using serological surveillance to inform the timing of COVID-19 boosters in Mozambique. We simulated using population-level seroprevalence thresholds as an estimate of the risk of outbreaks to trigger the timing of re-vaccination campaigns among older adults. We compare this approach to a strategy of re-vaccination at fixed time intervals. Vaccinating older adults each time the seroprevalence among older adults falls below 50% and 80% resulted in medians of 20% and 71% reduction in deaths, respectively, and number-needed-to-vaccinate to avert one death (NNT) of 1,499 (2.5th-97.5th centile:1,252-1,905) and 3,151 (2,943-3,429), respectively. In comparison, biennial and annual re-vaccination of older adults resulted in medians of 35% and 52% deaths averted, respectively, and NNTs of 1,443 (1,223-1,733) and 1,941 (1,805-2,112), respectively. We conducted sensitivity analysis over a range of antibody waning rates and epidemic scenarios and found that re-vaccination trigger thresholds of 50-60% seroprevalence are most likely to be efficient compared to fixed-time strategies. However, given marginal gains in efficiency even in the best-case scenarios, our results favor the use of simpler fixed-time strategies for long-term control of SARS-CoV-2.

Modelling the Interplay between Responsive Individual Vaccination Decisions and the Spread of SARS-CoV-2 (preprint)

The uptake of COVID-19 vaccines remains low despite their high effectiveness. Epidemic models that represent decision-making psychology can provide insight into the potential impact of vaccine promotion interventions in the context of the COVID-19 pandemic. We coupled a network-based mathematical model of SARS-CoV-2 transmission in Georgia, USA with a social-psychological vaccination decision-making model in which vaccine side effects, post-vaccination infections, and other unidentified community-level factors could "nudge" individuals towards vaccine resistance while hospitalization spikes could nudge them towards willingness. Combining an increased probability of hospitalization-prompted resistant-to-willing switches with a decreased probability of willing-to-resistant switches prompted by unidentified community-level factors increased vaccine uptake and decreased SARS-CoV-2 incidence by as much as 30.7% and 24.0%, respectively. The latter probability had a greater impact than the former. This illustrates the disease prevention potential of vaccine promotion interventions that address community-level factors influencing decision-making and anticipate the case curve instead of reacting to it.

Rapid review of social contact patterns during the COVID-19 pandemic (preprint)

Background: Physical distancing measures aim to reduce person-to-person contact, a key driver of transmission of respiratory infections such as SARS-CoV-2. In response to unprecedented restrictions on human contact during the COVID-19 pandemic, a number of studies measured social contact patterns under the implementation of physical distancing measures. This rapid review aims to synthesize empirical data on the changing social contact patterns during the COVID-19 pandemic. Method: We conducted a systematic review using PubMed, Medline, Embase and Google Scholar following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We descriptively compared the distribution of contacts observed during the pandemic to pre-COVID data across countries to explore changes in contact patterns during physical distancing measures. Results: We identified 12 studies that reported social contact patterns during the COVID-19 pandemic. The majority of studies (11/12) collected data during the initial mitigation period in the spring of 2020 marked by government-declared lockdowns and the most stringent physical distancing measures. Some studies collected additional data after relaxation of initial mitigation. Most study settings reported a mean of between 2-5 contacts per person per day, a substantial reduction compared to pre-COVID rates which ranged from 7-26 contacts per day in similar settings. This reduction was particularly pronounced for contacts outside of the home. Consequently, levels of assortative mixing by age substantially declined. After relaxation of initial mitigation, mean contact rates subsequently increased but did not return to pre-COVID levels. Increases in contacts post-relaxation were driven by working-age adults. Conclusion: Information on changes in contact patterns during physical distancing measures can guide more realistic representations of contact patterns in mathematical models for SARS-CoV-2 transmission.

Social contact patterns among employees in 3 U.S. companies during early phases of the COVID-19 pandemic, April to June 2020. (preprint)

2.ImportanceDevising control strategies against diseases such as COVID-19 require understanding of contextual social mixing and contact patterns. There has been no standardized multi-site social contact study conducted in workplace settings in the United States that can be used to broadly inform pandemic preparedness policy in these settings. ObjectiveThe study aimed to characterize the patterns of social contacts and mixing across workplace environments, including on-site or when teleworking. DesignThis was a cross-sectional non-probability survey that used standardized social contact diaries to collect data. Employees were requested to record their physical and non-physical contacts in a diary over two consecutive days, documented at the end of each day. Employees from each company were enrolled through email and electronic diaries sent as individual links. Data were collected from April to June 2020. SettingTwo multinational consulting companies and one university administrative department, all located in Georgia, USA. ParticipantsEmployees opted into the study by accepting the invitation on a link sent via email. Main OutcomeThe outcome was median number of contacts per person per day. This was stratified by day of data collection, age, sex, race and ethnicity. ResultsOf 3,835 employees approached, 357 (9.3%) completed the first day of contact diary of which 304 completed both days of contact diary. There was a median of 2 contacts (IQR: 1-4, range: 0-21) per respondent on both day one and two. The majority (55%) of contacts involved conversation only, occurred at home (64%), and cumulatively lasted more than 4 hours (38%). Most contacts were repeated, and within same age groups, though participants aged 30-59 years reported substantial inter-generational mixing with children. ConclusionParticipating employees in 3 surveyed workplaces reported few contacts, similar to studies from the UK and China when shelter-in-place orders were in effect during the pandemic. Many contacts were repeated which may limit the spread of infection. Future rounds are planned to assess changes in contact patterns when employees resume work in the office after the lockdown due to COVID-19 pandemic.

Projected HIV and Bacterial STI Incidence Following COVID-Related Sexual Distancing and Clinical Service Interruption (preprint)

BackgroundThe global COVID-19 pandemic has the potential to indirectly impact the transmission dynamics and prevention of HIV and other sexually transmitted infections (STI). Studies have already documented reductions in sexual activity ("sexual distancing") and interruptions in HIV/STI services, but it is unknown what combined impact these two forces will have on longer-term HIV/STI epidemic trajectories. MethodsWe adapted a network-based model of co-circulating HIV, gonorrhea, and chlamydia for a population of men who have sex with men (MSM) in the Atlanta area. Model scenarios varied the timing, overlap, and relative extent of COVID-related sexual distancing in casual and one-time partnership networks and service interruption within four service categories (HIV screening, HIV PrEP, HIV ART, and STI treatment). ResultsA 50% relative decrease in sexual partnerships and interruption of all clinical services, both lasting 18 months, would generally offset each other for HIV (total 5-year population impact for Atlanta MSM: -227 cases), but have net protective effect for STIs (-23,800 cases). Greater relative reductions and longer durations of service interruption would increase HIV and STI incidence, while greater relative reductions and longer durations of sexual distancing would decrease incidence of both. If distancing lasted only 3 months but service interruption lasted 18 months, the total 5-year population impact would be an additional 890 HIV cases and 57,500 STI cases. ConclusionsThe counterbalancing impact of sexual distancing and clinical service interruption depends on the infection and the extent and durability of these COVID-related changes. If sexual behavior rebounds while service interruption persists, we project an excess of hundreds of HIV cases and thousands of STI cases just among Atlanta MSM over the next 5 years. Immediate action to limit the impact of service interruptions is needed to address the indirect effects of the global COVID pandemic on the HIV/STI epidemic.

Modeling Dynamic Network Strategies for SARS-CoV-2 Control on a Cruise Ship (preprint)

SARS-CoV-2 outbreaks have occurred on several nautical vessels, driven by the high-density contact networks on these ships. Optimal strategies for prevention and control that account for realistic contact networks are needed. We developed a network-based transmission model for SARS-CoV-2 on the Diamond Princess outbreak to characterize transmission dynamics and to estimate the epidemiological impact of outbreak control and prevention measures. This model represented the dynamic multi-layer network structure of passenger-passenger, passenger-crew, and crew-crew contacts, both before and after the large-scale network lockdown imposed on the ship in response to the disease outbreak. Model scenarios evaluated variations in the timing of the network lockdown, reduction in contact intensity within the sub-networks, and diagnosis-based case isolation on outbreak prevention. We found that only extreme restrictions in contact patterns during network lockdown and idealistic clinical response scenarios could avert a major COVID-19 outbreak. Contact network changes associated with adequate outbreak prevention were the restriction of passengers to their cabins, with limited passenger-crew contacts. Clinical response strategies required for outbreak prevention included early mass screening with an ideal PCR test (100% sensitivity) and immediate case isolation upon diagnosis. Public health restrictions on optional leisure activities like these should be considered until longer-term effective solutions such as a COVID-19 vaccine become widely available.