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BackgroundStudies of COVID-19 vaccine effectiveness show increases in COVID-19 cases within 14 days of a first dose, potentially reflecting post-vaccination behaviour changes associated with SARS-CoV-2 transmission before vaccine protection. However, direct evidence for a relationship between vaccination and behaviour is lacking. We aimed to examine the association between vaccination status and self-reported non-household contacts and non-essential activities during a national lockdown in England and Wales. MethodsParticipants (n=1,154) who had received the first dose of a COVID-19 vaccine reported non-household contacts and non-essential activities from February to March 2021 in monthly surveys during a national lockdown in England and Wales. We used a case-crossover study design and conditional logistic regression to examine the association between vaccination status (pre-vaccination vs. 14 days post-vaccination) and self-reported contacts and activities within individuals. Stratified subgroup analyses examined potential effect heterogeneity by sociodemographic characteristics such as sex, household income or age group. Results457/1,154 (39.60%) participants reported non-household contacts post-vaccination compared with 371/1,154 (32.15%) participants pre-vaccination. 100/1,154 (8.67%) participants reported use of non-essential shops or services post-vaccination compared with 74/1,154 (6.41%) participants pre-vaccination. Post-vaccination status was associated with increased odds of reporting non-household contacts (OR 1.65, 95% CI 1.31-2.06, p<0.001) and use of non-essential shops or services (OR 1.50, 95% CI 1.03-2.17, p=0.032). This effect varied between men and women and different age groups. ConclusionParticipants had higher odds of reporting non-household contacts and use of non-essential shops or services within 14 days of their first COVID-19 vaccine compared to pre-vaccination. Public health emphasis on maintaining protective behaviours during this post-vaccination time period when individuals have yet to develop full protection from vaccination could reduce risk of SARS-CoV-2 infection.
ABSTRACT
BackgroundOccupational disparities in COVID-19 vaccine uptake can impact the effectiveness of vaccination programmes and introduce particular risk for vulnerable workers and those with high workplace exposure. This study aimed to investigate COVID-19 vaccine uptake by occupation, including for vulnerable groups and by occupational exposure status. MethodsWe used data from employed or self-employed adults who provided occupational information as part of the Virus Watch prospective cohort study (n=19,595) and linked this to study-obtained information about vulnerability-relevant characteristics (age, medical conditions, obesity status) and work-related COVID-19 exposure based on the Job Exposure Matrix. Participant vaccination status for the first, second, and third dose of any COVID-19 vaccine was obtained based on linkage to national records and study records. We calculated proportions and Sison-Glaz multinomial 95% confidence intervals for vaccine uptake by occupation overall, by vulnerability-relevant characteristics, and by job exposure. FindingsVaccination uptake across occupations ranged from 89-96% for the first dose, 87-94% for the second dose, and 75-86% for the third dose, with transport, trade, service and sales workers persistently demonstrating the lowest uptake. Vulnerable workers tended to demonstrate fewer between-occupational differences in uptake than non-vulnerable workers, although clinically vulnerable transport workers (76%-89% across doses) had lower uptake than several other occupational groups (maximum across doses 86-96%). Workers with low SARS-CoV-2 exposure risk had higher vaccine uptake (86%-96% across doses) than those with elevated or high risk (81-94% across doses). InterpretationDifferential vaccination uptake by occupation, particularly amongst vulnerable and highly-exposed workers, is likely to worsen occupational and related socioeconomic inequalities in infection outcomes. Further investigation into occupational and non-occupational factors influencing differential uptake is required to inform relevant interventions for future COVID-19 booster rollouts and similar vaccination programmes.
ABSTRACT
The two most commonly-used SARS-CoV-2 vaccines in the UK, BNT162b2 (Pfizer-BioNTech) and ChAdOx1 nCoV-19 (Oxford-AstraZeneca), employ different immunogenic mechanisms. Compared to BNT162b2, two-dose immunisation with ChAdOx1 induces substantially lower peak anti-spike antibody (anti-S) levels and is associated with a higher risk of breakthrough infections. To provide preliminary indication of how a third booster BNT162b2 dose impacts anti-S levels, we performed a cross-sectional analysis using capillary blood samples from vaccinated adults (aged [≥]18 years) participating in Virus Watch, a prospective community cohort study in England and Wales. Blood samples were analysed using Roche Elecsys Anti-SARS-CoV-2 S immunoassay. We analysed anti-S levels by week since the third dose for vaccines administered on or after September 1, 2021 and stratified the results by second dose vaccine type (ChAdOx1 or BNT162b2), age, sex and clinical vulnerability. Anti-S levels peaked at two weeks post-booster for BNT162b2 (22,185 U/mL; 95%CI: 21,406-22,990) and ChAdOx1 second dose recipients (19,203 U/mL; 95%CI: 18,094-20,377). These were higher than the corresponding peak antibody levels post-second dose for BNT162b2 (12,386 U/mL; 95%CI: 9,801-15,653, week 2) and ChAdOx1 (1,192 U/mL; 95%CI: 818-1735, week 3). No differences emerged by second dose vaccine type, age, sex or clinical vulnerability. Anti-S levels declined post-booster for BNT162b2 (half-life=44 days) and ChAdOx1 second dose recipients (half-life=40 days). These rates of decline were steeper than those post-second dose for BNT162b2 (half-life=54 days) and ChAdOx1 (half-life=80 days). Our findings suggest that peak anti-S levels are higher post-booster than post-second dose, but that levels are projected to be similar after six months for BNT162b2 recipients. Higher peak anti-S levels post-booster may partially explain the increased effectiveness of booster vaccination compared to two-dose vaccination against symptomatic infection with the Omicron variant. Faster waning trajectories post third-dose may have implications for the timing of future booster campaigns or four-dose vaccination regimens for the clinically vulnerable.
ABSTRACT
ImportanceThe Omicron (B.1.1.529) variant has increased SARs-CoV-2 infections in double vaccinated individuals globally, particularly in ChAdOx1 recipients. To tackle rising infections, the UK accelerated booster vaccination programmes used mRNA vaccines irrespective of an individuals primary course vaccine type with booster doses rolled out according to clinical priority. There is limited understanding of the effectiveness of different primary vaccination courses on mRNA based booster vaccines against SARs-COV-2 infections and how time-varying confounders can impact the evaluations comparing different vaccines as primary courses for mRNA boosters. ObjectiveTo evaluate the comparative effectiveness of ChAdOx1 versus BNT162b2 as primary doses against SARs-CoV-2 in booster vaccine recipients whilst accounting for time-varying confounders. DesignTrial emulation was used to reduce time-varying confounding-by-indication driven by prioritising booster vaccines based upon age, vulnerability and exposure status e.g. healthcare worker. Trial emulation was conducted by meta-analysing eight cohort results whose booster vaccinations were staggered between 16/09/2021 to 05/01/2022 and followed until 23/01/2022. Time from booster vaccination until SARS-CoV-2 infection, loss of follow-up or end-of-study was modelled using Cox proportional hazards models for each cohort and adjusted for age, sex, minority ethnic status, clinically vulnerability, and deprivation. SettingProspective observational study using the Virus Watch community cohort in England and Wales. ParticipantsPeople over the age of 18 years who had their booster vaccination between 16/09/2021 to 05/01/2022 without prior natural immunity. ExposuresChAdOx1 versus BNT162b2 as a primary dose, and an mRNA booster vaccine. ResultsAcross eight cohorts, 19,692 mRNA vaccine boosted participants were analysed with 12,036 ChAdOx1 and 7,656 BNT162b2 primary courses with a median follow-up time of 73 days (IQR:54-90). Median age, clinical vulnerability status and infection rates fluctuate through time. 7.2% (n=864) of boosted adults with ChAdOx1 primary course experienced a SARS-CoV-2 infection compared to 7.6% (n=582) of those with BNT162b2 primary course during follow-up. The pooled adjusted hazard ratio was 0.99 [95%CI:0.88-1.11], demonstrating no difference between the incidence of SARs-CoV-2 infections based upon the primary vaccine course. Conclusion and RelevanceIn mRNA boosted individuals, we found no difference in protection comparing those with a primary course of BNT162b2 to those with aChAdOx1 primary course. This contrasts with pre-booster findings where previous research shows greater effectiveness of BNT162b2 than ChAdOx1 in preventing infection.
ABSTRACT
IntroductionInfections of SARS-CoV-2 in vaccinated individuals have been increasing globally. Understanding the associations between vaccine type and a post-vaccination infection could help prevent further COVID-19 waves. In this paper, we use trial emulation to understand the impact of a phased introduction of the vaccine in the UK driven by vulnerability and exposure status. We estimate the comparative effectiveness of COVID-19 vaccines (ChAdOx1 versus BNT162b2) against post-vaccination infections of SARS-CoV-2 in a community setting in England and Wales. MethodTrial emulation was conducted by pooling results from six cohorts whose recruitment was staggered between 1st January 2021 and 31st March 2021 and followed until 12th November 2021. Eligibility for each trial was based upon age (18+ at the time of vaccination), without prior signs of infection or an infection within the first 14 days of the first dose. Time from vaccination of ChAdOx1 or BNT162b2 until SARS-CoV-2 infection (positive polymerase chain reaction or lateral flow test after 14 of the vaccination) was modelled using Cox proportional hazards model for each cohort and adjusted for age at vaccination, gender, minority ethnic status, clinically vulnerable status and index of multiple deprivation quintile. For those without SARS-CoV-2 infection during the study period, follow-up was until loss-of-follow-up or end of study (12th November 2021). Pooled hazard ratios were generated using random-effects meta-analysis. ResultsAcross six cohorts, there were a total of 21,283 participants who were eligible and vaccinated with either ChAdOx1 (n = 13,813) or BNT162b2 (n = 7,470) with a median follow-up time of 266 days (IQR: 235 - 282). By November 12th 2021, 750 (5.4%) adults who had ChAdOx1 as their vaccine experienced a SARS-CoV-2 infection, compared to 296 (4.0%) who had BNT162b2. We found that people who received ChAdOx1 vaccinations had 10.54 per 1000 people higher cumulative incidence for SARS-CoV-2 infection compared to BNT162b2 for infections during a maximum of 315 days of follow-up. When adjusted for age at vaccination, sex, minority ethnic status, index of multiple deprivation, and clinical vulnerability status, we found a pooled adjusted hazard ratio of 1.35 [HR: 1.35, 95%CI: 1.15 - 1.58], demonstrating a 35% increase in SARS-CoV-2 infections in people who received ChAdOx1 compared to BNT162b2. DiscussionWe found evidence of greater effectiveness of receiving BNT162b2 compared to ChAdOx1 vaccines against SARS-CoV-2 infection in England and Wales during a time period when Delta became the most prevalent variant of concern. Our findings demonstrate the importance of booster (third) doses to maintain protection and suggest that these should be prioritised to those who received ChAdOx1 as their primary course.
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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.
ABSTRACT
BackgroundWith the potential for and emergence of new COVID-19 variants, such as the reportedly more infectious Omicron, and their potential to escape the existing vaccines, understanding the relative importance of which non-household activities increase risk of acquisition of COVID-19 infection is vital to inform mitigation strategies. MethodsWithin an adult subset of the Virus Watch community cohort study, we sought to identify which non-household activities increased risk of acquisition of COVID-19 infection and which accounted for the greatest proportion of non-household acquired COVID-19 infections during the second wave of the pandemic. Among participants who were undertaking antibody tests and self-reporting PCR and lateral flow tests taken through the national testing programme, we identified those who were thought to be infected outside the household during the second wave of the pandemic. We used exposure data on attending work, using public or shared transport, using shops and other non-household activities taken from monthly surveys during the second wave of the pandemic. We used multivariable logistic regression models to assess the relative independent contribution of these exposures on risk of acquiring infection outside the household. We calculated Adjusted Population Attributable Fractions (APAF - the proportion of non-household transmission in the cohort thought to be attributable to each exposure) based on odds ratios and frequency of exposure in cases. ResultsBased on analysis of 10475 adult participants including 874 infections acquired outside the household, infection was independently associated with: leaving home for work (AOR 1.20 (1.02 - 1.42) p=0.0307, APAF 6.9%); public transport use (AOR for use more than once per week 1.82 (1.49 - 2.23) p<0.0001, APAF for public transport 12.42%); and shopping (AOR for shopping more than once per week 1.69 (1.29 - 2.21) P=0.0003, APAF for shopping 34.56%). Other non-household activities such as use of hospitality and leisure venues were rare due to restrictions and there were no significant associations with infection risk. ConclusionsA high proportion of the second wave of the pandemic was spent under conditions where people were being advised to work from home where possible, and to minimize exposure to shops, and a wide range of other businesses were subject to severe restrictions. Vaccines were being rolled out to high-risk groups. During this time, going to work was an important risk factor for infection but public transport use likely accounted for a lot of this risk. Only a minority of the cohort left home for work or used public or shared transport. By contrast, the majority of participants visited shops and this activity accounted for about one-third of non-household transmission.