Estimating the effectiveness of COVID-19 vaccination against COVID-19 hospitalisation and death: a cohort study based on the 2021 Census, England. (preprint)

Objective: To estimate the effectiveness of COVID-19 vaccination against hospitalisation for COVID-19 and death involving COVID-19 in England using linked population level data sources including the 2021 Census. Design: Retrospective cohort study. Setting: England, 21 March 2021 to 20 March 2022. Participants: Individuals alive and aged 16+ on 21 March 2021, resident in England, enumerated in the 2021 Census as a usual resident, and able to link to an NHS number. A sample of 583,840 individuals was used for the analysis. Exposures: COVID-19 vaccination: first dose, second dose and third dose/first booster dose, with categories for time since each dose. Main outcome measures: Hospitalisation for COVID-19 or death involving COVID-19. An adjusted Cox proportional hazard model was used to estimate the hazard ratio for the outcomes for vaccinated participants for different doses and time since dose compared to unvaccinated individuals. Vaccine effectiveness was estimated as (1 minus hazard ratio)x 100%. A control outcome of non-COVID-19 death was also assessed. Results: Vaccine effectiveness against hospitalisation for COVID-19 was 52.1% (95% confidence interval 51.3% to 52.8%) for a first dose, 55.6% (55.2% to 56.1%) for a second dose and 77.6% (77.3% to 78.0%) for a third dose, with a decrease in vaccine effectiveness 3+ months after the third dose. Vaccine effectiveness against COVID-19 mortality was 58.7% (52.7% to 63.9%) for a first dose, 88.5% (87.5% to 89.5%) for a second dose and 93.2% (92.9% to 93.5%) for a third dose, with evidence of waning 3+ months after the second and third doses. For the second dose, which is the most comparable across the different time-periods, vaccine effectiveness was higher against COVID-19 hospitalisation but slightly lower against COVID-19 mortality in the Omicron dominant period than the period before the Omicron variant became dominant. Vaccine effectiveness against both COVID-19 hospitalisation and mortality was higher in general for mRNA vaccines than non mRNA vaccines, however this could be influenced by the different populations given each vaccine vector. Non-zero VE against non-COVID-19 mortality indicates that residual confounding may impact the results, despite the inclusion of up-to-date socio-demographic adjustments and various sources of health data, with possible frailty bias, confounding by indication and a healthy vaccinee effect observed. Conclusions: The vaccine effectiveness estimates show increased protection with number of doses and a high level of protection against both COVID-19 hospitalisation and mortality for the third/booster dose, as would be expected from previous research. However, despite the various sources of health data used to adjust the models, the estimates for different breakdowns and for non-COVID-19 mortality expose residual confounding by health status, which should be considered when interpreting estimates of vaccine effectiveness.

Risk of death following SARS-CoV-2 infection or COVID-19 vaccination in young people in England: a self-controlled case series study (preprint)

Objectives: To assess whether there is a change in the incidence of cardiac and all-cause death in young people following COVID-19 vaccination or SARS-CoV-2 infection in unvaccinated individuals. Design: Self-controlled case series. Setting: National, linked electronic health record data in England. Study population: Individuals aged 12-29 who had received at least one dose of COVID-19 vaccination and died between 8 December 2020 and 2 February 2022 and registered by 16 February 2022 within 12 weeks of COVID-19 vaccination; Individuals aged 12-29 who died within 12 weeks of testing positive for SARS-CoV-2. Main outcome measures: Cardiac and all-cause deaths occurring within 12 weeks of vaccination or SARS-CoV-2 infection. Results: Compared to the baseline period, there was no evidence of a change in the incidence of cardiac death in the six weeks after vaccination, whether for each of weeks 1 to 6 or the whole six-week period. There was a decrease in the risk of all-cause death in the first week after vaccination and no change in each of weeks 2 to 6 after vaccination or whole six-week period after vaccination. Subgroup analyses by sex, age, vaccine type, and last dose also showed no change in the risk of death in the first six weeks after vaccination. There was a large increase in the incidence of cardiac and all-cause death in the overall risk period after SARS-CoV-2 infection among the unvaccinated. Conclusion: There is no evidence of an association between COVID-19 vaccination and an increased risk of death in young people. By contrast, SARS-CoV-2 infection was associated with substantially higher risk of cardiac related death and all-cause death.

Risk of COVID-19 related deaths for SARS-CoV-2 Omicron (B.1.1.529) compared with Delta (B.1.617.2) (preprint)

Objective To assess the risk of death involving COVID-19 following infection from Omicron (B.1.1.539/BA.1) relative to Delta (B.1.617.2). Design Retrospective cohort study. Setting England, UK, 1 December 2021 to 25 January 2022. Participants 1,035,163 people aged 18-100 years who tested positive for SARS-CoV-2 in the national surveillance programme, and had an infection identified as either Omicron- or Delta compatible. Main outcome measures Death involving COVID-19 as identified from death certification records. The exposure of interest was the SARS-CoV-2 variant identified from NHS Test and Trace PCR positive tests taken in the community (pillar 2) and analysed by Lighthouse laboratories. Cause-specific Cox proportional hazard regression models were adjusted for sex, age, vaccination status, previous infection, calendar time, ethnicity, Index of Multiple Deprivation rank, household deprivation, university degree, keyworker status, country of birth, main language, region, disability, and comorbidities. Additionally, we tested for interactions between variant and sex, age, vaccination status and comorbidities. Results The risk of death involving COVID-19 was 67% lower for Omicron compared to Delta and the reduction in the risk of death involving COVID-19 for Omicron compared to Delta was more pronounced in males than in females and in people under 70 years old than in people aged 70 years or over. Regardless of age, reduction of the risk of death from Omicron relative to Delta more was more pronounced in people who had received a booster than in those having received only two doses. Conclusions Our results support early work showing the relative reduction in severity of Omicron compared to Delta in terms of hospitalisation and extends this research to assess COVID-19 mortality. Our work also highlights the importance of the vaccination booster campaign, where the reduction in risk of death involving COVID-19 is most pronounced in individuals who had received a booster. What is already known on this topic The Omicron variant, which refers to the whole lineage (BA.1, BA.2, BA.3) had already been shown to be more transmissible than the Delta variant, but there is emerging evidence suggests that the risk of hospitalisation and risk of death within 28 days after a SARS-COV-2 test is lower. However, with a highly transmissible infection and high levels of population testing, definition of death within 28 days is more likely to be susceptible to misclassification bias due to asymptomatic or co-incidental infection. There is no study so far comparing the risk of COVID-19 death as identified from death certification records, with the cause of death assessed by the physician who attended the patient in the last illness. What this study adds Using data from a large cohort of COVID-19 infections that occurred in December 2021, we examined the difference in the risk COVID-19 death, as identified from death certification records, between the Delta and Omicron BA.1 variant. Our study shows that risk of death involving COVID-19 was reduced by 67% following infection with the Omicron BA.1 variant relative to the Delta variant after adjusting for a wide range of potential confounders, including vaccination status and comorbidities. Importantly, we found that the relative risk of COVID-19 mortality following Omicron versus Delta infection varied by age and sex, with lower relative risk in younger individuals and for males than females. The reduction in risk of death involving COVID-19 was also most pronounced in individuals who had received a booster.

Changes in the trajectory of Long Covid symptoms following COVID-19 vaccination: community-based cohort study (preprint)

ObjectiveTo estimate associations between COVID-19 vaccination and Long Covid symptoms in adults who were infected with SARS-CoV-2 prior to vaccination. DesignObservational cohort study using individual-level interrupted time series analysis. SettingRandom sample from the community population of the UK. Participants28,356 COVID-19 Infection Survey participants (mean age 46 years, 56% female, 89% white) aged 18 to 69 years who received at least their first vaccination after test-confirmed infection. Main outcome measuresPresence of long Covid symptoms at least 12 weeks after infection over the follow-up period 3 February to 5 September 2021. ResultsMedian follow-up was 141 days from first vaccination (among all participants) and 67 days from second vaccination (84% of participants). First vaccination was associated with an initial 12.8% decrease (95% confidence interval: -18.6% to -6.6%) in the odds of Long Covid, but increasing by 0.3% (-0.6% to +1.2%) per week after the first dose. Second vaccination was associated with an 8.8% decrease (-14.1% to -3.1%) in the odds of Long Covid, with the odds subsequently decreasing by 0.8% (-1.2% to -0.4%) per week. There was no statistical evidence of heterogeneity in associations between vaccination and Long Covid by socio-demographic characteristics, health status, whether hospitalised with acute COVID-19, vaccine type (adenovirus vector or mRNA), or duration from infection to vaccination. ConclusionsThe likelihood of Long Covid symptoms reduced after COVID-19 vaccination, and the improvement was sustained over the follow-up period after the second dose. Vaccination may contribute to a reduction in the population health burden of Long Covid, though longer follow-up time is needed. Summary boxWhat is already known on this topic O_LICOVID-19 vaccines are effective at reducing rates of SARS-CoV-2 infection, transmission, hospitalisation, and death C_LIO_LIThe incidence of Long Covid may be reduced if infected after vaccination, but the relationship between vaccination and pre-existing long COVID symptoms is unclear, as published studies are generally small and with self-selected participants C_LI What this study adds O_LIThe likelihood of Long Covid symptoms reduced after COVID-19 vaccination, and the improvement was sustained over the follow-up period after the second dose C_LIO_LIThere was no evidence of differences in this relationship by socio-demographic characteristics, health-related factors, vaccine type, or duration from infection to vaccination C_LIO_LIAlthough causality cannot be inferred from this observational evidence, vaccination may contribute to a reduction in the population health burden of Long Covid; further research is needed to understand the biological mechanisms that may ultimately contribute to the development of therapeutics for Long Covid C_LI

Estimating the effectiveness of first dose of COVID-19 vaccine against mortality in England: a quasi-experimental study (preprint)

BackgroundEstimating real-world vaccine effectiveness is vital to assess the impact of the vaccination programme on the pandemic and inform the ongoing policy response. However, estimating vaccine effectiveness using observational data is inherently challenging because of the non-randomised design and the potential for unmeasured confounding. MethodsWe used a Regression Discontinuity Design (RDD) to estimate vaccine effectiveness against COVID-19 mortality in England, exploiting the discontinuity in vaccination rates resulting from the UKs age-based vaccination priority groups. We used the fact that people aged 80 or over were prioritised for the vaccine roll-out in the UK to compare the risk of COVID-19 and non-COVID-19 death in people aged 75-79 and 80-84. FindingsThe prioritisation of vaccination of people aged 80 or above led to a large discrepancy in vaccination rates in people 80-84 compared to those 75-79 at the beginning of the vaccination campaign. We found a corresponding difference in COVID-19 mortality, but not in non-COVID-19 mortality, suggesting that our approach appropriately addresses the issue of unmeasured confounding factors. Our results suggest that the first vaccine dose reduced the risk of COVID-19 death by 52.6% (95% Cl 26.6-84.2) in those aged 80. InterpretationsOur results support existing evidence that a first dose of a COVID-19 vaccine has a strong protective effect against COVID-19 mortality in older adults. The RDD estimate of vaccine effectiveness is comparable to previously published studies using different methods, suggesting that unmeasured confounding factors are unlikely to substantially bias these studies. FundingOffice for National Statistics. Research in ContextO_ST_ABSEvidence before this studyC_ST_ABSWe searched PubMed for studies reporting on the real-world effectiveness of the COVID-19 vaccination on risk of death using terms such as "COVID-19", "vaccine effectiveness", "mortality" and "death". The relevant published studies on this topic report vaccine effectiveness estimates against risk of death ranging from 64.2% to 98.7%, for varying times post-vaccination. All of these are observational studies and therefore potentially subject to bias from unmeasured confounding. We found no studies that used a quasi-experimental method such as regression discontinuity design, which is not subject to bias from unmeasured confounding, to calculate the effectiveness of the COVID-19 vaccination on risk of COVID-19 death, or on other outcomes such as hospitalisation or infection. Added value of this studyThe estimates of vaccine effectiveness based on observational data may be biased by unmeasured confounding. This study uses a regression discontinuity design to estimate vaccine effectiveness, exploiting the fact that the vaccination campaign in the UK was rolled out following age-based priority groups. This enables the calculation of an unbiased estimate of the effectiveness of the COVID-19 vaccine against risk of death. The vaccine effectiveness estimate of 52.6% (95% Cl 26.6-84.2) is slightly lower but similar to previously published estimates, therefore suggesting that these estimates are not substantially affected by unmeasured confounding factors and confirming the effectiveness of the COVID-19 vaccine against risk of COVID-19 death. Implications of all the available evidenceObtaining an unbiased estimate of COVID-19 vaccine effectiveness is of vital importance in informing policy for lifting COVID-19 related measures. The regression discontinuity design provides confidence that the existing estimates from observational studies are unlikely to be substantially biased by unmeasured confounding.