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BackgroundWorkplaces are an important potential source of SARS-CoV-2 exposure; however, investigation into workplace contact patterns is lacking. This study aimed to investigate how workplace attendance and features of contact varied between occupations and over time during the COVID-19 pandemic in England. MethodsData were obtained from electronic contact diaries submitted between November 2020 and November 2021 by employed/self-employed prospective cohort study participants (n=4,616). We used mixed models to investigate the main effects and potential interactions between occupation and time for: workplace attendance, number of people in shared workspace, time spent sharing workspace, number of close contacts, and usage of face coverings. FindingsWorkplace attendance and contact patterns varied across occupations and time. The predicted probability of intense space sharing during the day was highest for healthcare (78% [95% CI: 75-81%]) and education workers (64% [59%-69%]), who also had the highest probabilities for larger numbers of close contacts (36% [32%-40%] and 38% [33%-43%] respectively). Education workers also demonstrated relatively low predicted probability (51% [44%-57%]) of wearing a face covering during close contact. Across all occupational groups, levels of workspace sharing and close contact were higher and usage of face coverings at work lower in later phases of the pandemic compared to earlier phases. InterpretationMajor variations in patterns of workplace contact and mask use are likely to contribute to differential COVID-19 risk. Across occupations, increasing workplace contact and reduced usage of face coverings presents an area of concern given ongoing high levels of community transmission and emergence of variants.
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BackgroundWorkers differ in their risk of SARS-CoV-2 infection according to their occupation, but the direct contribution of occupation to this relationship is unclear. This study aimed to investigate how infection risk differed across occupational groups in England and Wales up to April 2022, after adjustment for potential confounding and stratification by pandemic phase. MethodsData from 15,190 employed/self-employed participants in the Virus Watch prospective cohort study were used to generate risk ratios for virologically- or serologically-confirmed SARS-CoV-2 infection using robust Poisson regression, adjusting for socio-demographic and health-related factors and non-work public activities. We calculated attributable fractions (AF) amongst the exposed for belonging to each occupational group based on adjusted risk ratios (aRR). FindingsIncreased risk was seen in nurses (aRR=1.44, 1.25-1.65; AF=30%, 20-39%), doctors (aRR=1.33, 1.08-1.65; AF=25%, 7-39%), carers (1.45, 1.19-1.76; AF=31%, 16-43%), primary school teachers (aRR=1.67, 1.42-1.96; AF=40%, 30-49%), secondary school teachers (aRR=1.48, 1.26-1.72; AF=32%, 21-42%), and teaching support occupations (aRR=1.42, 1.23-1.64; AF=29%, 18-39%) compared to office-based professional occupations. Differential risk was apparent in the earlier phases (Feb 2020 - May 2021) and attenuated later (June - October 2021) for most groups, although teachers and teaching support workers demonstrated persistently elevated risk across waves. InterpretationOccupational differentials in SARS-CoV-2 infection risk vary over time and are robust to adjustment for socio-demographic, health-related, and non-workplace activity-related potential confounders. Direct investigation into workplace factors underlying elevated risk and how these change over time is needed to inform occupational health interventions.
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BackgroundSARS-CoV-2 vaccines stimulate production of antibodies targeting the spike protein (anti-S). The level of antibodies following vaccination and trajectories of waning may differ between vaccines influencing the level of protection, how soon protection is reduced and, consequently the optimum timing of booster doses. MethodsWe measured SARS-CoV-2 anti-S titre in the context of seronegativity for SARS-CoV-2 anti-Nucleocapsid (anti-N), in samples collected between 1st July and 24th October 2021 in a subset of adults in the Virus Watch community cohort. We compared anti-S levels after BNT162b2 (BioNTech/Pfizer) or ChAdOx1 (AstraZeneca/Oxford) vaccination using time since second dose of vaccination, age, sex and clinical vulnerability to investigate antibody waning. To investigate the use of anti-S levels as a correlate of protection against SARS-CoV-2 infection, we undertook a survival analysis (Kaplan-Meier and Cox) with individuals entering 21 days after their second dose of vaccine, or first antibody test after 1st July (whichever was latest) and exiting with the outcome of SARS-Cov-2 infection or at the end of follow up 24th October 2021. We also undertook a negative test design case-control analysis of infections occurring after the second vaccine dose (breakthrough infections) to determine whether the type of vaccine affected the risk of becoming infected. Results24049 samples from 8858 individuals (5549 who received a second dose of ChAdOx1 and 3205 BNT162b2) who remained anti-N negative were included in the analysis of anti-S waning over time. Three weeks after the second dose of vaccine BNT162b2 mean anti-S levels were 9039 (95%CI: 7946-10905) U/ml and ChadOx1 were 1025 (95%CI: 917-1146) U/ml. For both vaccines, waning anti-S levels followed a log linear decline from three weeks after the second dose of vaccination. At 20 weeks after the second dose of vaccine, the mean anti-S levels were 1521 (95%CI: 1432-1616) U/ml for BNT162b2 and 342 (95%CI: 322-365) U/ml for ChadOx1. We identified 197 breakthrough infections and found a reduced risk of infection post second dose of vaccine for individuals with anti-S levels greater than or equal to 500 U/ml compared to those with levels under 500 U/ml (HR 0.62; 95%CIs:0.44-0.87; p=0.007). Time to reach an anti-S threshold of 500 U/ml was estimated at 96 days for ChAdOx1 and 257 days for BNT162b2. We found an increased risk of a breakthrough infection for those who received the ChAdOx1 compared to those who received BNT162b2 (OR: 1.43, 95% CIs:1.18-1.73, p<0.001). DiscussionAnti-S levels are substantially higher following the second dose of BNT162b2 compared to ChAdOx1. There is a log linear waning in levels for both vaccines following the second dose. Anti-S levels are an important correlate of protection as demonstrated by those with anti-S levels < 500U/ml following vaccination being at significantly greater risk of subsequent infection. Since anti-S levels are substantially lower in ChAdOx1 than in BNT162b2 and both decline at similar rates we would expect waning immunity to occur earlier in ChAdOx1 compared to BNT162b2. Our results showing an increased risk of breakthrough infections for those who were vaccinated with ChAdOx1 compared to BNT162b2 are in line with this hypothesis. Consistent with our data, national analyses of vaccine effectiveness also suggest that waning of immunity for infection and, to a lesser extent for severe disease, is seen earlier in ChAdOx1 than in BNT162b2. Our data demonstrate the importance of booster doses to maintain protection in the elderly and clinically vulnerable and suggest that these should be prioritised to those who received ChAdOx1 as their primary course.
