COVID-19 Infection Risk amongst 14,104 Vaccinated Care Home Residents: A national observational longitudinal cohort study in Wales, United Kingdom, December 2020 to March 2021 (preprint)

BackgroundVaccinations for COVID-19 have been prioritised for older people living in care homes. However, vaccination trials included limited numbers of older people. AimWe aimed to study infection rates of SARS-CoV-2 for older care home residents following vaccination and identify factors associated with increased risk of infection. Study Design and SettingWe conducted an observational data-linkage study including 14,104 vaccinated older care home residents in Wales (UK) using anonymised electronic health records and administrative data. MethodsWe used Cox proportional hazards models to estimate hazard ratios (HRs) for the risk of testing positive for SARS-CoV-2 infection following vaccination, after landmark times of either 7 or 21-days post-vaccination. We adjusted hazard ratios for age, sex, frailty, prior SARS-CoV-2 infections and vaccination type. ResultsWe observed a small proportion of care home residents with positive PCR tests following vaccination 1.05% (N=148), with 90% of infections occurring within 28-days. For the 7-day landmark analysis we found a reduced risk of SARS-CoV-2 infection for vaccinated individuals who had a previous infection; HR (95% confidence interval) 0.54 (0.30,0.95), and an increased HR for those receiving the Pfizer-BioNTECH vaccine compared to the Oxford-AstraZeneca; 3.83 (2.45,5.98). For the 21-day landmark analysis we observed high HRs for individuals with low and intermediate frailty compared to those without; 4.59 (1.23,17.12) and 4.85 (1.68,14.04) respectively. ConclusionsIncreased risk of infection after 21-days was associated with frailty. We found most infections occurred within 28-days of vaccination, suggesting extra precautions to reduce transmission risk should be taken in this time frame.

Intensity of COVID-19 in care homes following Hospital Discharge in the early stages of the UK epidemic (preprint)

Background A defining feature of the COVID-19 pandemic in many countries was the tragic extent to which care home residents were affected, and the difficulty preventing introduction and subsequent spread of infection. Management of risk in care homes requires good evidence on the most important transmission pathways. One hypothesised route at the start of the pandemic, prior to widespread testing, was transfer of patients from hospitals, which were experiencing high levels of nosocomial events. Methods We tested the hypothesis that hospital discharge events increased the intensity of care home cases using a national individually linked health record cohort in Wales, UK. We monitored 186,772 hospital discharge events over the period March to July 2020, tracking individuals to 923 care homes and recording the daily case rate in the homes populated by 15,772 residents. We estimated the risk of an increase in cases rates following exposure to a hospital discharge using multi-level hierarchical logistic regression, and a novel stochastic Hawkes process outbreak model. Findings In regression analysis, after adjusting for care home size, we found no significant association between hospital discharge and subsequent increases in care home case numbers (odds ratio: 0.99, 95% CI 0.82, 1.90). Risk factors for increased cases included care home size, care home resident density, and provision of nursing care. Using our outbreak model, we found a significant effect of hospital discharge on the subsequent intensity of cases. However, the effect was small, and considerably less than the effect of care home size, suggesting the highest risk of introduction came from interaction with the community. We estimated approximately 1.8% of hospital discharged patients may have been infected. Interpretation There is growing evidence in the UK that the risk of transfer of COVID-19 from the high-risk hospital setting to the high-risk care home setting during the early stages of the pandemic was relatively small. Although access to testing was limited to initial symptomatic cases in each care home at this time, our results suggest that reduced numbers of discharges, selection of patients, and action taken within care homes following transfer all may have contributed to mitigation. The precise key transmission routes from the community remain to be quantified.

Staff-Pupil SARS-CoV-2 Infection Pathways in Schools: A Population Level Linked Data Approach (preprint)

Abstract Background: Better understanding of the role that children and school staff play in the transmission of SARS-CoV-2 is essential to guide policy development on controlling infection whilst minimising disruption to children's education and wellbeing. Methods: Our national e-cohort (n=500,779) study used anonymised linked data for pupils, staff and associated households linked via educational settings. We estimated the risk of testing positive for SARS-CoV-2 infection for staff and pupils over the period August-December 2020, dependent on measures of recent exposure to known cases linked to their educational settings. Results: The total number of cases in a school was not associated with a subsequent increase in the risk of testing positive (Staff OR per case 0.92, 95%CI 0.85, 1.00; Pupils OR per case 0.98, 95%CI 0.93, 1.02). Amongst pupils, the number of recent cases within the same year group was significantly associated with subsequent increased risk of testing positive (OR per case 1.12, 95%CI 1.08 - 1.15). These effects were adjusted for a range of demographic covariates, and in particular any known cases within the same household, which had the strongest association with testing positive (Staff OR 39.86, 95%CI 35.01, 45.38, pupil OR 9.39, 95%CI 8.94 - 9.88). Conclusions: In a national school cohort, the odds of staff testing positive for SARS-CoV-2 infection were not significantly increased in the 14-day period after case detection in the school. However, pupils were found to be at increased risk, following cases appearing within their own year group, where most of their contacts occur. Strong mitigation measures over the whole of the study period may have reduced wider spread within the school environment.

COVID-19 control across urban-rural gradients (preprint)

Controlling the regional re-emergence of SARS-CoV-2 after its initial spread in ever-changing personal contact networks and disease landscapes is a challenging task. In a landscape context, contact opportunities within and between populations are changing rapidly as lockdown measures are relaxed and a number of social activities re-activated. Using an individual-based metapopulation model, we explored the efficacy of different control strategies across an urban-rural gradient in Wales, UK. Our model shows that isolation of symptomatic cases, or regional lockdowns in response to local outbreaks, have limited efficacy unless the overall transmission rate is kept persistently low. Additional isolation of non-symptomatic infected individuals, who may be detected by effective test and trace strategies, is pivotal to reduce the overall epidemic size over a wider range of transmission scenarios. We define an urban-rural gradient in epidemic size as a correlation between regional epidemic size and connectivity within the region, with more highly connected urban populations experiencing relatively larger outbreaks. For interventions focused on regional lockdowns, the strength of such gradients in epidemic size increased with higher travel frequencies, indicating a reduced efficacy of the control measure in the urban regions under these conditions. When both non-symptomatic and symptomatic individuals are isolated or regional lockdown strategies are enforced, we further found the strongest urban-rural epidemic gradients at high transmission rates. This effect was reversed for strategies targeted at symptomatics only. Our results emphasise the importance of test-and-tracing strategies and maintaining low transmission rates for efficiently controlling COVID19 spread, both at landscape scale and in urban areas.

Risk factors for outbreaks of COVID-19 in care homes following hospital discharge: a national cohort analysis (preprint)

BackgroundAdult residential and nursing care homes are settings in which older and often vulnerable people live in close proximity. This population experiences a higher proportion of respiratory and gastrointestinal illnesses than the general population and has been shown to have a high morbidity and mortality in relation to COVID-19. MethodsWe examined 3,115 hospital discharges to 1,068 Welsh adult care homes and the subsequent outbreaks of COVID-19 occurring over an 18 week period between 22 February and 27 June 2020. A Cox proportional hazards regression model was used to assess the impact of time-dependent exposure to hospital discharge on the incidence of the first known outbreak, over a window of 7-21 days after discharge, and adjusted for care home characteristics, including size, type of provision and health board. ResultsA total of 330 homes experienced an outbreak of COVID-19, and 544 homes received a discharge from hospital over the study period. The exposure to discharge from hospital was not associated with a significant increase in the risk of a new outbreak (hazard ratio 1{middle dot}15, 95% CI 0{middle dot}89, 1{middle dot}47, p = 0{middle dot}29) after adjusting for care home characteristics. Care home size was by far the most significant predictor. Hazard ratios (95% CI) in comparison to homes of <10 residents were: 3{middle dot}40 (1{middle dot}99, 5{middle dot}80) for 10-24 residents; 8{middle dot}25 (4{middle dot}93, 13{middle dot}81) for 25-49 residents; and 17{middle dot}35 (9{middle dot}65, 31{middle dot}19) for homes of 50+ residents. When stratified for care home size, the outbreak rates were similar for periods when homes were exposed to a hospital discharge, in comparison to periods when homes were unexposed. ConclusionOur analyses showed that large homes were at considerably greater risk of outbreaks throughout the epidemic, and after adjusting for care home size, a discharge from hospital was not associated with a significant increase in risk. Research in contextO_ST_ABSWhat is already known on this subjectC_ST_ABSO_LICare home populations experience more respiratory outbreaks than the general population1 and older people have been more severely affected by COVID-19, with a case fatality proportion of 2{middle dot}3% overall but 8% in those aged 70-79 and 14{middle dot}8% in those aged over 802 C_LIO_LIEvidence and modelling suggested that up to half of all COVID-19 fatalities could come from the care home population3 and that testing prior to hospital discharge was not always available or undertaken9 C_LIO_LIType and use of PPE6 and the number of staff employed can have an impact on care home outbreaks of COVID-196,7 C_LI What this study addsO_LIOur analysis found no effect of hospital discharges on care home outbreaks once care home size had been adjusted for. In line with previous studies, larger care homes were much more likely to experience an outbreak C_LI