Comparative effectiveness and safety of homologous two-dose ChAdOx1 versus heterologous vaccination with ChAdOx1 and BNT162b2

Mechanistic models of humoral kinetics following COVID-19 vaccination

COVID-19 vaccine programmes must account for variable immune responses and waning protection. Existing descriptions of antibody responses to COVID-19 vaccination convey limited information about the mechanisms of antibody production and maintenance. We describe antibody dynamics after COVID-19 vaccination with two biologically motivated mathematical models. We fit the models using Markov chain Monte Carlo to seroprevalence data from 14 602 uninfected individuals in England between May 2020 and September 2022. We analyse the effect of age, vaccine type, number of doses and the interval between doses on antibody production and longevity. We find evidence that individuals over 35 years old twice vaccinated with ChAdOx1-S generate a persistent antibody response suggestive of long-lived plasma cell induction. We also find that plasmablast productive capacity is greater in: younger people than older people (≤4.5-fold change in point estimates); people vaccinated with two doses than one dose (≤12-fold change); and people vaccinated with BNT162b2 than ChAdOx1-S (≤440-fold change). We find the half-life of an antibody to be 23-106 days. Routinely collected seroprevalence data are invaluable for characterizing within-host mechanisms of antibody production and persistence. Extended sampling and linking seroprevalence data to outcomes would enable conclusions about how humoral kinetics protect against disease.

SpiN-Tec: A T cell-based recombinant vaccine that is safe, immunogenic, and shows high efficacy in experimental models challenged with SARS-CoV-2 variants of concern

The emergence of new SARS-CoV-2 variants of concern associated with waning immunity induced by natural infection or vaccines currently in use suggests that the COVID-19 pandemic will become endemic. Investing in new booster vaccines using different platforms is a promising way to enhance protection and keep the disease under control. Here, we evaluated the immunogenicity, efficacy, and safety of the SpiN-Tec vaccine, based on a chimeric recombinant protein (SpiN) adjuvanted with CTVad1 (MF59-based adjuvant), aiming at boosting immunity against variants of concern of SARS-CoV-2. Immunization of K18-hACE-2 transgenic mice and hamsters induced high antibody titers and cellular immune response to the SpiN protein as well as to its components, RBD and N proteins. Importantly in a heterologous prime/boost protocol with a COVID-19 vaccine approved for emergency use (ChAdOx1), SpiN-Tec enhanced the level of circulation neutralizing antibodies (nAb). In addition to protection against the Wuhan isolate, protection against the Delta and Omicron variants was also observed as shown by reduced viral load and lung pathology. Toxicity and safety tests performed in rats demonstrated that the SpiN-Tec vaccine was safe and, based on these results, the SpiN-Tec phase I/II clinical trial was approved.

Comparative effectiveness of monovalent XBB.1.5 containing covid-19 mRNA vaccines in Denmark, Finland, and Sweden: target trial emulation based on registry data

ABSTRACT

Objective

To estimate the effectiveness of vaccination with a monovalent covid-19 mRNA vaccine containing the omicron XBB.1.5 subvariant against severe covid-19 disease in Denmark, Finland, and Sweden.

Design

Target trial emulation based on registry data.

Setting

Denmark, Finland, and Sweden, 1 October 2023 to 21 April 2024.

Participants

Source population of 3 898 264 individuals eligible for vaccination with the XBB.1.5 containing covid-19 mRNA vaccine at the start of the study on 1 October 2023. Study cohort comprised 1 876 282 recipients of an XBB.1.5 containing vaccine during the study period matched with 1 876 282 non-recipients. Individuals were aged ≥65 years (mean age 75.4 years, standard deviation 7.4 years) and had received at least four doses of a previous covid-19 vaccine.

Main outcome measures

Cumulative incidences of hospital admissions and deaths related to covid-19 in a follow-up period of 24 weeks after immunisation (defined as one week after vaccination) in recipients of an XBB.1.5 containing covid-19 mRNA vaccine and matched non-recipients. Cumulative incidences were used to calculate comparative vaccine effectiveness (1-risk ratio) and risk differences.

Results

The associated comparative vaccine effectiveness was 57.9% (95% confidence interval (CI) 49.9% to 65.8%) against hospital admission for covid-19 (1085 v 2635 events) and 75.2% (70.6% to 79.9%) against deaths related to covid-19 disease (348 v 1458 events) after 24 weeks of follow-up. This result corresponded to 154.7 (95% CI 78.3 to 231.0) hospital admissions for covid-19 and 120.3 (110.5 to 130.2) deaths prevented per 100 000 individuals who were vaccinated with an XBB.1.5 containing vaccine. The associated comparative vaccine effectiveness was similar irrespective of sex, age group (65-74 v ≥75 years), number of doses of previous covid-19 vaccines, subgroup of co-administered seasonal influenza vaccines, and period of when either the omicron XBB or BA.2.86 sublineage was predominant. Although the observed reduction in risk was highest during the first weeks after vaccination, comparative vaccine effectiveness was well maintained after 24 weeks of follow-up.

Conclusions

In this study, in adults aged ≥65 years, vaccination with a monovalent XBB.1.5 containing covid-19 mRNA vaccine was associated with reduced rates of hospital admissions for covid-19 and deaths related to covid-19, during the autumn and winter of 2023-24 in Denmark, Finland, and Sweden.

Effectiveness of nirsevimab immunoprophylaxis against respiratory syncytial virus-related outcomes in hospital and primary care settings: a retrospective cohort study in infants in Catalonia (Spain)

BACKGROUND

In Catalonia, infants under 6 months old were eligible to receive nirsevimab, a novel monoclonal antibody against respiratory syncytial virus (RSV). We aimed to analyse nirsevimab's effectiveness across primary and hospital care outcomes.

METHODS

Retrospective cohort study from 1 October 2023 to 31 January 2024, including all infants born between April and September 2023. We established two cohorts based on nirsevimab administration (immunised and non-immunised). We followed individuals until the earliest moment of an outcome-RSV infection, primary care attended bronchiolitis and pneumonia, hospital emergency visits due to bronchiolitis, hospital admission or intensive care unit (ICU) admission due to RSV bronchiolitis-death or the end of the study. We used the Kaplan-Meier estimator and fitted Cox regression models using a calendar time scale to estimate HRs and their 95% CIs.

RESULTS

Among 26 525 infants, a dose of nirsevimab led to an adjusted HR for hospital admission due to RSV bronchiolitis of 0.124 (95% CI: 0.086 to 0.179) and an adjusted HR for ICU admission of 0.099 (95% CI: 0.041 to 0.237). Additionally, the adjusted HRs observed for emergency visits were 0.446 (95% CI: 0.385 to 0.516) and 0.393 (95% CI: 0.203 to 0.758) for viral pneumonia, 0.519 (95% CI: 0.467 to 0.576) for bronchiolitis attended in primary care and 0.311 (95% CI: 0.200 to 0.483) for RSV infection.

CONCLUSION

We demonstrated nirsevimab's effectiveness with reductions of 87.6% and 90.1% in hospital and ICU admissions, respectively. These findings offer crucial guidance for public health authorities in implementing RSV immunisation campaigns.

Rapid Decline of SARS-CoV-2 Viral Load in Single vs. Double-Dose (Short-Interval <6 Weeks) ChAdOx nCoV-19 Vaccinated Health-Care Workers

The present work was carried out during the emergence of Delta Variant of Concern (VoC) and aimed to study the change in SARS CoV-2 viral load in Covishield vaccinated asymptomatic/mildly symptomatic health-care workers (HCWs) to find out the optimum isolation period. The SARS CoV-2 viral load was carried out in sequential samples of 55 eligible HCWs which included unvaccinated (UnV; n = 11), single-dose vaccinated (SDV, n = 20) and double-dose vaccinated [DDV, n = 24; short-interval (<6 weeks)] subjects. The mean load of envelope (E) gene on day 5 in SDV [0.42 × 105 copies/reaction] was significantly lower as compared to DDV [6.3 × 105 copies/reaction, P = 0.005] and UnV [6.6 × 105 copies/reaction, P = 0.001] groups. The rate of decline of SARS CoV-2 viral load in the initial 5 days of PCR positivity was significantly higher in SDV as compared to that in DDV (Mean log decline 0.39 vs. 0.19; P < 0.001). This was possibly due to interference of adenoviral immunity of first dose of adenovirus-vectored vaccine in double-dose vaccinated HCWs who had received vaccines within a shorter interval (<6 weeks).

Advances in methodologies of negative controls: a scoping review

OBJECTIVES

Negative controls are considered an important tool to mitigate biases in observational studies. The aim of this scoping review was to summarize current methodologies of negative controls (both negative control exposure [NCE] and negative control outcome [NCO]).

STUDY DESIGN AND SETTING

We searched PubMed, Web of Science, Embase, and Cochrane Library (up to March 9, 2023) for articles on methodologies of negative controls. Two reviewers selected eligible studies and collected relevant data independently and in duplicate. We reported total numbers and percentages, and summarized methodologies narratively.

RESULTS

A total of 37 relevant methodological articles were included in our review. These publications covered NCE (n = 11, 29.8%), NCO (n = 13, 35.1%), or both (n = 13, 35.1%), with most focused on bias detection (n = 14, 37.8%), bias correction (n = 16, 43.3%), and P value or confidence interval (CI) calibration (n = 5, 13.5%). For the two remaining articles (5.4%), one discussed bias detection and P value or CI calibration and the other covered all the three functions. For bias detection, the existence of an association between the NCE (NCO) and outcome (exposure) variables of interest simply indicates that results may suffer from confounding bias, selection bias and/or information bias. For bias correction, however, the algorithms of negative control methods need more stringent assumptions such as rank preservation, monotonicity, and linearity.

CONCLUSION

Negative controls can be leveraged for bias detection, P value or CI calibration, and bias correction, among which bias correction has been the most studied methodologically. The current available methods need some stringent assumptions to detect or remove bias. More methodological research is needed to optimize the use of negative controls.

Safety and immunogenicity of heterologous ChAdOx1-nCoV19 and BNT162b2 vaccination: A meta-analysis of the heterologous COVID-19 vaccination outcomes

INTRODUCTION

Here, we systematically assessed the safety and immunogenicity of the heterologous ChAd/BNT vaccination regimens.

MATERIALS AND METHODS

We evaluated the immunogenicity by the geometric mean titers ratio (GMTR) of the neutralizing antibody and anti-spike IgG. The safety of heterologous ChAd/BNT vaccination was evaluated using the pooled risk ratios (RRs) calculated by the random-effects model about the adverse events. Our study was registered with PROSPERO, CRD42021265165.

RESULTS

Eleven studies were included in the analyses. Compared to the homologous ChAd/ChAd vaccination, the heterologous ChAd/BNT vaccination showed significantly higher immunogenicity in terms of the neutralizing antibody and GMTR of anti-spike IgG, but at the same time displayed higher incidence of total adverse reactions, especially for the local adverse reactions. Moreover, heterologous ChAd/BNT vaccination showed similar immunogenicity to the homologous BNT/BNT vaccination (GMTR of neutralizing antibody and anti-spike IgG) and similar safety.

DISCUSSION

Heterologous ChAd/BNT vaccination showed robust immunogenicity and tolerable safety.

Safety of heterologous primary and booster schedules with ChAdOx1-S and BNT162b2 or mRNA-1273 vaccines: nationwide cohort study

OBJECTIVE

To assess the risk of adverse events associated with heterologous primary (two dose) and booster (three dose) vaccine schedules for covid-19 with Oxford-AstraZeneca's ChAdOx1-S priming followed by mRNA vaccines (Pfizer-BioNTech's BNT162b2 or Moderna's mRNA-1273) as compared with homologous mRNA vaccine schedules for covid-19.

DESIGN

Nationwide cohort study.

SETTING

Denmark, 1 January 2021 to 26 March 2022.

PARTICIPANTS

Adults aged 18-65 years who received a heterologous vaccine schedule of priming with ChAdOx1-S and one or two mRNA booster doses (with either the BNT162b2 or mRNA-1273 vaccine) were compared with adults who received a homologous BNT162b2 or mRNA-1273 vaccine schedule (ie, two dose v two dose, and three dose v three dose schedule).

MAIN OUTCOME MEASURES

The incidence of hospital contacts for a range of adverse cardiovascular and haemostatic events within 28 days after the second or third vaccine dose, comparing heterologous versus homologous vaccine schedules. Secondary outcomes included additional prioritised adverse events of special interest. Poisson regression was used to estimate incidence rate ratios with adjustment for selected covariates.

RESULTS

Individuals who had had a heterologous primary vaccine (n=137 495) or a homologous vaccine (n=2 688 142) were identified, in addition to those who had had a heterologous booster (n=129 770) or a homologous booster (n=2 197 213). Adjusted incidence rate ratios of adverse cardiovascular and haemostatic events within 28 days for the heterologous primary and booster vaccine schedules in comparison with the homologous mRNA vaccine schedules were 1.22 (95% confidence interval 0.79 to 1.91) and 1.00 (0.58 to 1.72) for ischaemic cardiac events, 0.74 (0.40 to 1.34) and 0.72 (0.37 to 1.42) for cerebrovascular events, 1.12 (0.13 to 9.58) and 4.74 (0.94 to 24.01) for arterial thromboembolisms, 0.79 (0.45 to 1.38) and 1.09 (0.60 to 1.98) for venous thromboembolisms, 0.84 (0.18 to 3.96) and 1.04 (0.60 to 4.55) for myocarditis or pericarditis, 0.97 (0.45 to 2.10) and 0.89 (0.21 to 3.77) for thrombocytopenia and coagulative disorders, and 1.39 (1.01 to 1.91) and 1.02 (0.70 to 1.47) for other bleeding events, respectively. No associations with any of the outcomes were found when restricting to serious adverse events defined as stay in hospital for more than 24 h.

CONCLUSION

Heterologous primary and booster covid-19 vaccine schedules of ChAdOx1-S priming and mRNA booster doses as both second and third doses were not associated with increased risk of serious adverse events compared with homologous mRNA vaccine schedules. These results are reassuring but given the rarity of some of the adverse events, associations cannot be excluded.

Effectiveness of heterologous and homologous covid-19 vaccine regimens: living systematic review with network meta-analysis

OBJECTIVE

To evaluate the effectiveness of heterologous and homologous covid-19 vaccine regimens with and without boosting in preventing covid-19 related infection, hospital admission, and death.

DESIGN

Living systematic review and network meta-analysis.

DATA SOURCES

World Health Organization covid-19 databases, including 38 sources of published studies and preprints.

STUDY SELECTION

Randomised controlled trials, cohort studies, and case-control studies.

METHODS

38 WHO covid-19 databases were searched on a weekly basis from 8 March 2022 to 31 July 2022. Studies that assessed the effectiveness of heterologous and homologous covid-19 vaccine regimens with or without a booster were identified. Studies were eligible when they reported the number of documented, symptomatic, severe covid-19 infections, covid-19 related hospital admissions, or covid-19 related deaths among populations that were vaccinated and unvaccinated. The primary measure was vaccine effectiveness calculated as 1−odds ratio. Secondary measures were surface under the cumulative ranking curve (SUCRA) scores and the relative effects for pairwise comparisons. The risk of bias was evaluated by using the risk of bias in non-randomised studies of interventions (ROBINS-I) tool for all cohort and case-control studies. The Cochrane risk of bias tool (version 2; ROB-2) was used to assess randomised controlled trials.

RESULTS

The second iteration of the analysis comprised 63 studies. 25 combinations of covid-19 vaccine regimens were identified, of which three doses of mRNA vaccine were found to be 93% (95% credible interval 70% to 98%) effective against asymptomatic or symptomatic covid-19 infections for non-delta or non-omicron related infections. Heterologous boosting using two dose adenovirus vector vaccines with one dose mRNA vaccine showed a vaccine effectiveness of 94% (72% to 99%) against non-delta or non-omicron related asymptomatic or symptomatic infections. Three doses of mRNA vaccine were found to be the most effective in reducing non-delta or non-omicron related hospital admission (96%, 82% to 99%). The vaccine effectiveness against death in people who received three doses of mRNA vaccine remains uncertain owing to confounders. The estimate for a four dose mRNA vaccine regimen was of low certainty, as only one study on the effectiveness of four doses could be included in this update. More evidence on four dose regimens will be needed to accurately assess the effectiveness of a fourth vaccine dose. For people with delta or omicron related infection, a two dose regimen of an adenovirus vector vaccine with one dose of mRNA booster was 77% (42% to 91%) effective against asymptomatic or symptomatic covid-19 infections, and a three dose regimen of a mRNA vaccine was 93% (76% to 98%) effective against covid-19 related hospital admission.

CONCLUSION

An mRNA booster is recommended to supplement any primary vaccine course. Heterologous and homologous three dose regimens work comparably well in preventing covid-19 infections, even against different variants. The effectiveness of three dose vaccine regimens against covid-19 related death remains uncertain.

SYSTEMATIC REVIEW REGISTRATION

This review was not registered. The protocol is included in the supplementary document.

READERS' NOTE

This article is a living systematic review that will be updated to reflect emerging evidence. Updates may occur for up to two years from the date of original publication. This version is update 1 of the original article published on 31 May 2022 (BMJ 2022;377:e069989), and previous versions can be found as data supplements (https://www.bmj.com/content/377/bmj-2022-069989/related). When citing this paper please consider adding the version number and date of access for clarity.