Covid-19 vaccine safety in pregnancy, a nested case-control study in births from April 2021 to March 2022, England (preprint)

Introduction: Vaccine safety in pregnancy is always of paramount importance. Current evidence of COVID-19 vaccine safety in pregnancy has been reassuring with no association found with negative maternal and neonatal outcomes. However, very few safety studies are conducted on a national level and investigate dosage, timing of vaccination as well as vaccine manufacturer. To fill this knowledge gap, we conducted a population based COVID-19 vaccine safety evaluation in England, including timing of vaccination by trimester, dosage and vaccine manufacturer received in pregnancy. Method: A matched case control study nested in a retrospective cohort where adverse maternal and neonatal pregnancy outcomes were compared across several COVID-19 vaccine exposures using conditional multivariable logistic regression, adjusting for a range of demographic and health characteristics. Eligible participants were identified from the national maternity services dataset (MSDS) and records were linked to hospital admission, national COVID-19 vaccine and COVID-19 testing databases. Matching criteria differed by outcome but included participant's age and estimated week of conception. Results: 514,013 pregnant individuals aged between 18 and 50 years were identified during the study period (births from 16th of April 2021- 31st March 2022). Receiving at least one dose of COVID-19 vaccine during pregnancy conferred lower odds of giving birth to a baby who was low birthweight (aOR=0.86, 95% CI: 0.79 - 0.93), preterm (aOR=0.89, 95% CI: 0.85 - 0.92) or who had an Apgar score less than 7 at five mins of age (aOR=0.89, 95% CI: 0.80 - 0.98). There was no association between vaccination in pregnancy and stillbirth (aOR=0.90, 95% CI: 0.76 - 1.07), neonatal death (aOR=1.27, 95% CI: 0.91 - 1.77) perinatal death (aOR=0.98, 95% CI: 0.83 - 1.16), and maternal venous thromboembolism in pregnancy (aOR=0.82, 95% CI: 0.43 - 1.56). The odds of maternal admission to intensive care unit were lower in vaccinated pregnant women (aOR=0.85, 95% CI: 0.76 - 0.95). Conclusion: COVID-19 vaccines are safe to use in pregnancy and they confer protection against SARS-CoV-2 infection which can lead to adverse outcomes for both the mother and the infant. Our findings generated important information to communicate to pregnant women and health professionals to support COVID-19 maternal vaccination programmes.

Understanding reported COVID-19 cases in England following changes to testing, between November 2021 and April 2022 (preprint)

Background Over the course of the pandemic, testing policies for SARS-CoV-2 have varied considerably in England, particularly in the five months up to 1 April 2022 when free community testing ended. We described the trends and demographics of COVID-19 cases during this period. Methods COVID-19 cases reported between 15 November 2021 and 30 April 2022 were extracted and aggregated by testing pillar: Pillar 1 for those tested within the NHS, private or public health laboratories, and Pillar 2 for community testing. COVID-19 cases were described by epi-week, and stratified by test type, age, sex, index of multiple deprivation (IMD), region, and population density. Incidence rates were also calculated and stratified by IMD and region. Results Of 10,196,425 COVID-19 cases, 7.3% were reported under Pillar 1 and 92.7% under Pillar 2. From 15 November 2021 to 31 March 2022, most Pillar 2 cases were tested either by polymerase chain reaction (PCR) only or PCR with lateral flow device (LFD) (70.8%) and three in ten cases tested using LFD only. However, between 1 April and 30 April 2022 this rose to nine out of ten cases testing using LFD only. Over the whole period studied and under both pillars, the majority of cases were female (55.2%), resided in the South East (17.0%) and in the age group 30-39 years (18.6%). Trends in IMD and population density varied over the period. When stratifying by IMD the highest case numbers and incidence rates reported under Pillar 1 and NHS were in those in the most deprived quintile. This was also seen for cases reported under Pillar 2 by LFD until 11 January 2022, where a reverse in the trend occurred with the highest cases and rates in the least deprived quintile. This same pattern was observed when describing the cases by population density, with Pillar 2 LFD reported cases being highest in the most densely populated regions until 11 January, from when there was a switch to the highest cases being in the least densely populated regions. Conclusion Differences and trends were observed in reported COVID-19 cases in England, particularly those tested under Pillar 2 following the introduction of testing policy changes. To better understand the impact of these changes over the course of the COVID-19 pandemic, as well as to predict the impact of future testing policies, it would be beneficial to investigate the accessibility of testing amongst different populations. Currently, Pillar 1 COVID-19 cases are likely to be more representative of symptomatic cases requiring testing for a clinical need, as these are less impacted by variations in testing patterns compared to Pillar 2. However, a limitation of that approach is that use of Pillar 1 alone would be biased towards those more likely to be clinically unwell.

Comparative transmission of SARS-CoV-2 Omicron (B.1.1.529) and Delta (B.1.617.2) variants and the impact of vaccination: national cohort study, England (preprint)

Background The SARS-CoV-2 Omicron variant (B.1.1.529) has rapidly replaced the Delta variant (B.1.617.2) to become dominant in England. This epidemiological study assessed differences in transmissibility between the Omicron and Delta using two methods and data sources. Methods Omicron and Delta cases were identified through genomic sequencing, genotyping and S-gene target failure in England from 5-11 December 2021. Secondary attack rates for Omicron and Delta using named contacts and household clustering were calculated using national surveillance and contact tracing data. Logistic regression was used to control for factors associated with transmission. Findings Analysis of contact tracing data identified elevated secondary attack rates for Omicron vs Delta in household (15.0% vs 10.8%) and non-household (8.2% vs 3.7%) settings. The proportion of index cases resulting in residential clustering was twice as high for Omicron (16.1%) compared to Delta (7.3%). Transmission was significantly less likely from cases, or in named contacts, in receipt of three compared to two vaccine doses in household settings, but less pronounced for Omicron (aRR 0.78 and 0.88) compared to Delta (aRR 0.62 and 0.68). In non-household settings, a similar reduction was observed for Delta cases and contacts (aRR 0.84 and 0.51) but only for Omicron contacts (aRR 0.76, 95% CI: 0.58-0.93) and not cases in receipt of three vs two doses (aRR 0.95, 0.77-1.16). Interpretation Our study identified increased risk of onward transmission of Omicron, consistent with its successful global displacement of Delta. We identified a reduced effectiveness of vaccination in lowering risk of transmission, a likely contributor for the rapid propagation of Omicron.

Effectiveness of COVID-19 vaccines against the Omicron (B.1.1.529) variant of concern (preprint)

Abstract Background A rapid increase in cases due to the SARS-CoV-2 Omicron (B.1.1.529) variant in highly vaccinated populations has raised concerns about the effectiveness of current vaccines. Methods We used a test-negative case-control design to estimate vaccine effectiveness (VE) against symptomatic disease caused by the Omicron and Delta variants in England. VE was calculated after primary immunisation with two BNT162b2 or ChAdOx1 doses, and at 2+ weeks following a BNT162b2 booster. Results Between 27 November and 06 December 2021, 581 and 56,439 eligible Omicron and Delta cases respectively were identified. There were 130,867 eligible test-negative controls. There was no effect against Omicron from 15 weeks after two ChAdOx1 doses, while VE after two BNT162b2 doses was 88.0% (95%CI: 65.9 to 95.8%) 2-9 weeks after dose 2, dropping to between 34 and 37% from 15 weeks post dose 2.From two weeks after a BNT162b2 booster, VE increased to 71.4% (95%CI: 41.8 to 86.0%) for ChAdOx1 primary course recipients and 75.5% (95%CI: 56.1 to 86.3%) for BNT162b2 primary course recipients. For cases with Delta, VE was 41.8% (95%CI: 39.4-44.1%) at 25+ weeks after two ChAdOx1 doses, increasing to 93.8% (95%CI: 93.2-94.3%) after a BNT162b2 booster. With a BNT162b2 primary course, VE was 63.5% (95%CI: 61.4 to 65.5%) 25+ weeks after dose 2, increasing to 92.6% (95%CI: 92.0-93.1%) two weeks after the booster. Conclusions Primary immunisation with two BNT162b2 or ChAdOx1 doses provided no or limited protection against symptomatic disease with the Omicron variant. Boosting with BNT162b2 following either primary course significantly increased protection.

Emergence of the Delta Variant and risk of SARS-CoV-2 infection in secondary school students and staff: prospective surveillance in 18 schools, England (preprint)

Background The role of educational settings on SARS-CoV-2 infection and transmission remains controversial. We investigated SARS-CoV-2 infection, seroprevalence and seroconversions rates in secondary schools during the 2020/21 academic year, which included the emergence of the more transmissible Alpha and Delta variants, in England. Methods The UK Health Security Agency (UKHSA) initiated prospective surveillance in 18 urban English secondary schools. Participants had nasal swabs for SARS-CoV-2 RT-PCR and blood sampling for SARS-CoV-2 Nucleoprotein and Spike protein antibodies at the start (Round 1: September-October 2020) and end (Round 2: December 2021) of the autumn term, when schools reopened after national lockdown was imposed in January 2021 (Round 3: March-April) and end of the academic year (Round 4: May-July). Findings We enrolled 2,314 participants (1277 students, 1037 staff). In-school testing identified 31 PCR-positive participants (20 students, 11 staff). Another 247 confirmed cases (112 students, 135 staff) were identified after linkage with national surveillance data, giving an overall positivity rate of 12.0% (278/2313; staff [14.1%, 146/1037] vs students [10.3%, 132/1276; p=0.006). Nucleoprotein-antibody seroprevalence increased for students and staff between Rounds 1-3 but changed little in Round 4, when the Delta variant was the dominant circulating strain. Overall, Nucleoprotein-antibody seroconversion was 18.4% (137/744) in staff and 18.8% (146/778) in students, while Spike-antibody seroconversion was higher in staff (72.8% (525/721) than students (21.3%, 163/764) because of vaccination. Interpretation SARS-CoV-2 infection and transmission in secondary schools remained low when community infection rates were low because of national lockdown, even after the emergence of the Delta variant

Long-term health-related quality of life in non-hospitalised COVID-19 cases with confirmed SARS-CoV-2 infection in England: Longitudinal analysis and cross-sectional comparison with controls (preprint)

Background This study measured the long-term health-related quality of life of non-hospitalised COVID-19 cases with PCR-confirmed SARS-CoV-2(+) infection using the recommended instrument in England (the EQ-5D). Methods Prospective cohort study of SARS-CoV-2(+) cases aged 12-85 years and followed up for six months from 01 December 2020, with cross-sectional comparison to SARS-CoV-2(-) controls. Main outcomes were loss of quality-adjusted life days (QALDs); physical symptoms; and COVID-19-related private expenditures. We analysed results using multivariable regressions with post-hoc weighting by age and sex, and conditional logistic regressions for the association of each symptom and EQ-5D limitation on cases and controls. Results Of 548 cases (mean age 41.1 years; 61.5% female), 16.8% reported physical symptoms at month 6 (most frequently extreme tiredness, headache, loss of taste and/or smell, and shortness of breath). Cases reported more limitations with doing usual activities than controls. Almost half of cases spent a mean of £18.1 on non-prescription drugs (median: £10.0), and 52.7% missed work or school for a mean of 12 days (median: 10). On average, all cases lost 15.9 (95%-CI: 12.1, 19.7) QALDs, while those reporting symptoms at month 6 lost 34.1 (29.0, 39.2) QALDs. Losses also increased with older age. Cumulatively, the health loss from morbidity contributes at least 21% of the total COVID-19-related disease burden in England. Conclusions One in 6 cases report ongoing symptoms at 6 months, and 10% report prolonged loss of function compared to pre-COVID-19 baselines. A marked health burden was observed among older COVID-19 cases and those with persistent physical symptoms. summary Losses of health-related quality of life in non-hospitalised COVID-19 cases increase by age and for cases with symptoms after 6 months. At a population level, at least 21% of the total COVID-19-related disease burden in England is attributable to morbidity.

Secondary Attack Rates in Primary and Secondary School Bubbles Following a Confirmed Case: Active, Prospective National Surveillance, November to December 2020, England (preprint)

Background: Following the full re-opening of schools in England and emergence of the SARS-CoV-2 Alpha variant, we investigated the risk of SARS-CoV-2 infection in students and staff who were contacts of a confirmed case in a school bubble (school groupings with limited interactions), along with their household members. Methods: Primary and secondary school bubbles were recruited into sKIDsBUBBLE after being sent home to self-isolate following a confirmed case of COVID-19 in the bubble. Bubble participants and their household members were sent home-testing kits comprising nasal swabs for RT-PCR testing and whole genome sequencing, and oral fluid swabs for SARS-CoV-2 antibodies. Results: During November-December 2020, 14 bubbles were recruited from 7 schools, including 269 bubble contacts (248 students, 21 staff) and 823 household contacts (524 adults, 299 children). The secondary attack rate was 10.0% (6/60) in primary and 3.9% (4/102) in secondary school students, compared to 6.3% (1/16) and 0% (0/1) among staff, respectively. The incidence rate for household contacts of primary school students was 6.6% (12/183) and 3.7% (1/27) for household contacts of primary school staff. In secondary schools, this was 3.5% (11/317) and 0% (0/1), respectively. Household contacts were more likely to test positive if their bubble contact tested positive although there were new infections among household contacts of uninfected bubble contacts. Interpretation: Compared to other institutional settings, the overall risk of secondary infection in school bubbles and their household contacts was low. Our findings are important for developing evidence-based infection prevention guidelines for educational settings.

Emergence of SARS-CoV-2 Alpha (B.1.1.7) variant, infection rates, antibody seroconversion and seroprevalence rates in secondary school students and staff: active prospective surveillance, December 2020 to March 2021, England (preprint)

Background In England, the rapid spread of the SARS-Cov-2 Alpha (B.1.1.7) variant from November 2020 led to national lockdown, including school closures in January 2021. We assessed SARS-CoV-2 infection, seroprevalence and seroconversion in students and staff when secondary schools reopened in March 2021. Methods Public Health England initiated SARS-CoV-2 surveillance in 18 secondary schools across six regions in September 2020. Participants provided nasal swabs for RT-PCR and blood samples for SARS-CoV-2 antibodies at the beginning (September 2020) and end (December 2020) of the autumn term and at the start of the spring term (March 2021). Findings In March 2021, 1895 participants (1100 students, 795 staff) were tested; 5.6% (61/1094) students and 4.4% (35/792) staff had laboratory-confirmed SARS-CoV-2 infection between December 2020 and March 2021. Nucleoprotein antibody seroprevalence was 36.3% (370/1018) in students and 31.9% (245/769) in staff, while spike protein antibody prevalence was 39.5% (402/1018) and 59.8% (459/769), respectively, similar to regional community seroprevalence. Between December 2020 and March 2021 (median 15.9 weeks), 14.8% (97/656; 95% CI: 12.2-17.7) students and 10.0% (59/590; 95% CI: 7.7-12.7) staff seroconverted. Weekly seroconversion rates were similar from September to December 2020 (8.0/1000) and from December 2020 to March 2021 (7.9/1000; students: 9.3/1,000; staff: 6.3/1,000). Interpretation By March 2021, a third of secondary school students and staff had serological evidence of prior infection based on N-antibody seropositivity, and an additional third of staff had evidence of vaccine-induced immunity based on S-antibody seropositivity. Further studies are needed to assess the impact of the Delta variant. Research in Context Evidence Before this study The Alpha variant is 30-70% more transmissible than previously circulating SARS-CoV-2 strains in adults and children. One outbreak investigation in childcare settings estimated similar secondary attack rates with the Alpha variant in children and adults. There are limited data on the impact of the Alpha variant in educational settings. In England, cases in primary and secondary school aged children increased rapidly from late November 2020 and peaked at the end of December 2020, leading to national lockdown including school closures. Added Value of This Study Seroconversion rates in staff and students during December 2020 to March 2021, when the Alpha variant was the primary circulating strain in England, were similar to the period between September 2020 and December 2020 when schools were fully open for in-person teaching. By March 2021, a third of students overall and more than half the students in some regions were seropositive for SARS-CoV-2 antibodies. Among staff, too, around a third had evidence of prior infection on serological testing and a further third had vaccine-induced immunity. Implications of all the Available Evidence SARS-CoV-2 antibody seroprevalence was high among secondary school students in March 2021 and is likely to be higher following the emergence of an even more transmissible Delta variant in May 2021. Education staff are increasingly being protected by the national COVID-19 immunisation programme. These findings have important implications for countries that are considering vaccination of children to control the pandemic

Implementation of COVID-19 Preventive Measures in Primary and Secondary Schools Following Reopening of Schools in Autumn 2020; A Cross-Sectional Study of Parents' and Teachers' Experiences in England (preprint)

Objective The main objective was to assess implementation of and ease of implementation of control measures in schools as reported by staff and parents. Design Cross-sectional study. Setting Staff and parents/guardian participants in the 132 primary schools and 20 secondary schools participating in sKIDs and sKIDsPLUS surveillances. Main outcome measure Prevalence of control measures implemented in Autumn 2020, parental and staff perception of ease of implementation and acceptability of conducting school surveillance studies. Results In total, 56/152 (37%) schools participating in Public Health England's sKIDs study of COVID in schools accepted the invitation to participate in the survey. By 28 December 2020, 1,953 parent and 986 staff respondents had completed the online questionnaire. While more than half the parents were positive about their children returning to school, roughly a third reported being a little anxious. 90% and 82% of primary and secondary school parents were either completely or partly reassured by the preventive measures implemented in their schools. Among staff, 80% of primary staff and 87% of secondary school staff felt that they were at higher risk of COVID-19 because of their profession; only 52% of primary school staff and 38% of secondary school staff reportedly felt safe. According to the teaching staff, most preventive measures were well-implemented apart from requiring 2-metre distancing between staff. For students, maintaining the 2-metre distance was reported to be particularly difficult. By extension, secondary schools also struggled to maintain small groups at all times or ensuring that the same staff were assigned to each student group (a problem also commonly reported by parents). Conclusions Variable implementation of infection control measures was reported by staff and parents. Whilst the majority were not worried about returning to school, some parents and staff, were concerned about returning to school and the risks posed to children, staff and household members.

Assessment of Mortality and Hospital Admissions Associated with Confirmed Infection with SARS-CoV-2 Variant of Concern VOC-202012/01 (B.1.1.7) a Matched Cohort and Time-to-Event Analysis (preprint)

Background: The emergence of VOC202012/01 in England, known as B.1.1.7 or informally as the ‘UK variant’, has coincided with rapid increases in the number of PCR-confirmed positive cases in areas where the variant has been concentrated. Methods: To assess whether infection with SARS-CoV-2 variant VOC202012/01 is associated with more severe clinical outcomes compared to wild-type infection, genomically sequenced and confirmed variant and wild-type cases were linked to routine healthcare and surveillance datasets. Two statistical analyses were conducted to compare the risk of hospital admission and death within 28 days of test between variant and wild-type cases: a case-control study and an adjusted Cox proportional hazards model. Differences in severity of disease were assessed by comparing hospital admission and mortality, including length of hospitalisation and time to death.Results: Of 63,609 genomically sequenced COVID-19 cases tested in England between October and December 2020 6,038 were variant cases. In the matched cohort analysis 2,821 variant cases were matched to 2,821 to wild-type cases. In the time to event analysis we observed a 34% increased risk in hospitalisation associated with the variant compared to wild-type cases, however, no significant difference in the risk of mortality was observed. Conclusion: We found evidence of increased risk of hospitalisation after adjusting for key confounders, suggesting increase infection severity associated with this variant. Follow-up studies are needed to assess potential longer-term differences in the clinical outcomes of people infected with the VOC-202012/01 variant.

Do antibody positive healthcare workers have lower SARS-CoV-2 infection rates than antibody negative healthcare workers? Large multi-centre prospective cohort study (the SIREN study), England: June to November 2020 (preprint)

BackgroundThere is an urgent need to better understand whether individuals who have recovered from COVID-19 are protected from future SARS-CoV-2 infection. MethodsA large multi-centre prospective cohort was recruited from publicly funded hospital staff in the UK. Participants attended regular SARS-CoV-2 PCR and antibody testing (every 2-4 weeks) and completed fortnightly questionnaires on symptoms and exposures. At enrolment, participants were assigned to either the positive cohort (antibody positive or prior PCR/antibody test positive) or negative cohort (antibody negative, not previously known to be PCR/antibody positive). Potential reinfections were clinically reviewed and classified according to case definitions (confirmed, probable, possible (subdivided by symptom-status)) depending on hierarchy of evidence. Individuals in the primary infection were excluded from this analysis if infection was confirmed by antibody only. Reinfection rates in the positive cohort were compared against new PCR positives in the negative cohort using a mixed effective multivariable logistic regression analysis. FindingsBetween 18 June and 09 November 2020, 44 reinfections (2 probable, 42 possible) were detected in the baseline positive cohort of 6,614 participants, collectively contributing 1,339,078 days of follow-up. This compares with 318 new PCR positive infections and 94 antibody seroconversions in the negative cohort of 14,173 participants, contributing 1,868,646 days of follow-up. The incidence density per 100,000 person days between June and November 2020 was 3.3 reinfections in the positive cohort, compared with 22.4 new PCR confirmed infections in the negative cohort. The adjusted odds ratio was 0.17 for all reinfections (95% CI 0.13-0.24) compared to PCR confirmed primary infections. The median interval between primary infection and reinfection was over 160 days. InterpretationA prior history of SARS-CoV-2 infection was associated with an 83% lower risk of infection, with median protective effect observed five months following primary infection. This is the minimum likely effect as seroconversions were not included. FundingDepartment of Health and Social Care and Public Health England, with contributions from the Scottish, Welsh and Northern Irish governments.

Nowcasting CoVID-19 Deaths in England by Age and Region (preprint)

Understanding the trajectory of the daily numbers of deaths in people with CoVID-19 is essential to decisions on the response to the CoVID-19 pandemic. Estimating this trajectory from data on numbers of deaths is complicated by the delay between deaths occurring and their being reported to the authorities. In England, Public Health England receives death reports from a number of sources and the reporting delay is typically several days, but can be several weeks. Delayed reporting results in considerable uncertainty about the number of deaths that occurred on the most recent days. In this article, we estimate the number of deaths per day in each of five age strata within seven English regions. We use a Bayesian hierarchical model that involves a submodel for the number of deaths per day and a submodel for the reporting delay distribution. This model accounts for reporting-day effects and longer-term changes over time in the delay distribution. We show how the model can be fitted in a computationally efficient way when the delay distribution is same in multiple strata, e.g. over a wide range of ages.