Induction of trained immunity by influenza vaccination - impact on COVID-19.

Non-specific protective effects of certain vaccines have been reported, and long-term boosting of innate immunity, termed trained immunity, has been proposed as one of the mechanisms mediating these effects. Several epidemiological studies suggested cross-protection between influenza vaccination and COVID-19. In a large academic Dutch hospital, we found that SARS-CoV-2 infection was less common among employees who had received a previous influenza vaccination: relative risk reductions of 37% and 49% were observed following influenza vaccination during the first and second COVID-19 waves, respectively. The quadrivalent inactivated influenza vaccine induced a trained immunity program that boosted innate immune responses against various viral stimuli and fine-tuned the anti-SARS-CoV-2 response, which may result in better protection against COVID-19. Influenza vaccination led to transcriptional reprogramming of monocytes and reduced systemic inflammation. These epidemiological and immunological data argue for potential benefits of influenza vaccination against COVID-19, and future randomized trials are warranted to test this possibility.

Efficacy of BCG Vaccination Against Respiratory Tract Infections in Older Adults During the Coronavirus Disease 2019 Pandemic.

BACKGROUND: Older age is associated with increased severity and death from respiratory infections, including coronavirus disease 2019 (COVID-19). The tuberculosis BCG vaccine may provide heterologous protection against nontuberculous infections and has been proposed as a potential preventive strategy against COVID-19. METHODS: In this multicenter, placebo-controlled trial, we randomly assigned older adults (aged ≥60 years; n = 2014) to intracutaneous vaccination with BCG vaccine (n = 1008) or placebo (n = 1006). The primary end point was the cumulative incidence of respiratory tract infections (RTIs) that required medical intervention, during 12 months of follow-up. Secondary end points included the incidence of COVID-19, and the effect of BCG vaccination on the cellular and humoral immune responses. RESULTS: The cumulative incidence of RTIs requiring medical intervention was 0.029 in the BCG-vaccinated group and 0.024 in the control group (subdistribution hazard ratio, 1.26 [98.2% confidence interval, .65-2.44]). In the BCG vaccine and placebo groups, 51 and 48 individuals, respectively tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with polymerase chain reaction (subdistribution hazard ratio, 1.053 [95% confidence interval, .71-1.56]). No difference was observed in the frequency of adverse events. BCG vaccination was associated with enhanced cytokine responses after influenza, and also partially associated after SARS-CoV-2 stimulation. In patients diagnosed with COVID-19, antibody responses after infection were significantly stronger if the volunteers had previously received BCG vaccine. CONCLUSIONS: BCG vaccination had no effect on the incidence of RTIs, including SARS-CoV-2 infection, in older adult volunteers. However, it improved cytokine responses stimulated by influenza and SARS-CoV-2 and induced stronger antibody titers after COVID-19 infection. CLINICAL TRIALS REGISTRATION: EU Clinical Trials Register 2020-001591-15 ClinicalTrials.gov NCT04417335.

Interleukin 38 reduces antigen-presentation capacity and antibody production after vaccination.

The mechanisms that underpin low vaccine responses, which can lead to inadequate protection against infection, are still partially unclear. Interleukin (IL)-38 is a member of the IL-1 family, expressed by B cells among others, that regulates inflammatory responses. A recent study shows that IL-38 suppresses plasma cell generation and antibody production upon immune activation. We hypothesis that IL-38 affects antigen-presentation capacity of innate immune cells, effecting antibody production. Here, we investigated the effect of recombinant human IL-38 on human peripheral blood mononuclear cells and myeloid-derived DCs regarding cytokine production, phagocytosis, and expression of MCH II and co-stimulatory proteins in vitro, and further relate circulating plasma IL-38 concentrations to antibody responses in a cohort of 75 females aged 18-48 vaccinated with BCG and Tdap-IPV. To this end, we found that IL-38 decreased the expression of HLA-DR, HLA-DM, and CD83 on PBMCs, and CD40 and CD86 on MDDCs. IL-38 further impaired phagocytosis capacity of monocytes. Lastly, antibody production against diphtheria toxoids up to eight months post-vaccination was negatively associated with IL-38 plasma concentrations. These data suggest that IL-38 could dampen the effectiveness of antigen-presentation and phagocytosis, and could therefore modulate the immunogenicity of some vaccine types.

Determinants of Systemic SARS-CoV-2-Specific Antibody Responses to Infection and to Vaccination: A Secondary Analysis of Randomised Controlled Trial Data.

SARS-CoV-2 infections elicit antibodies against the viral spike (S) and nucleocapsid (N) proteins; COVID-19 vaccines against the S-protein only. The BCG-Corona trial, initiated in March 2020 in SARS-CoV-2-naïve Dutch healthcare workers, captured several epidemic peaks and the introduction of COVID-19 vaccines during the one-year follow-up. We assessed determinants of systemic anti-S1 and anti-N immunoglobulin type G (IgG) responses using trial data. Participants were randomised to BCG or placebo vaccination, reported daily symptoms, SARS-CoV-2 test results, and COVID-19 vaccinations, and donated blood for SARS-CoV-2 serology at two time points. In the 970 participants, anti-S1 geometric mean antibody concentrations (GMCs) were much higher than anti-N GMCs. Anti-S1 GMCs significantly increased with increasing number of immune events (SARS-CoV-2 infection or COVID-19 vaccination): 104.7 international units (IU)/mL, 955.0 IU/mL, and 2290.9 IU/mL for one, two, and three immune events, respectively (p < 0.001). In adjusted multivariable linear regression models, anti-S1 and anti-N log10 concentrations were significantly associated with infection severity, and anti-S1 log10 concentration with COVID-19 vaccine type/dose. In univariable models, anti-N log10 concentration was also significantly associated with acute infection duration, and severity and duration of individual symptoms. Antibody concentrations were not associated with long COVID or long-term loss of smell/taste.

The impact of circadian rhythm on Bacillus Calmette-Guérin vaccination effects on SARS-CoV-2 infections.

Background and objective: A recent study has suggested that circadian rhythm has an important impact on the immunological effects induced by Bacillus Calmette-Guérin (BCG) vaccination. The objective of this study was to evaluate whether the timing of BCG vaccination (morning or afternoon) affects its impact on severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infections and clinically relevant respiratory tract infections (RTIs). Methods: This is a post-hoc analysis of the BCG-CORONA-ELDERLY (NCT04417335) multicenter, placebo-controlled trial, in which participants aged 60 years and older were randomly assigned to vaccination with BCG or placebo, and followed for 12 months. The primary endpoint was the cumulative incidence of SARS-CoV-2 infection. To assess the impact of circadian rhythm on the BCG effects, participants were divided into four groups: vaccinated with either BCG or placebo in the morning (between 9:00h and 11:30h) or in the afternoon (between 14:30h and 18:00h). Results: The subdistribution hazard ratio of SARS-CoV-2 infection in the first six months after vaccination was 2.394 (95% confidence interval [CI], 0.856-6.696) for the morning BCG group and 0.284 (95% CI, 0.055-1.480) for the afternoon BCG group. When comparing those two groups, the interaction hazard ratio was 8.966 (95% CI, 1.366-58.836). In the period from six months until 12 months after vaccination cumulative incidences of SARS-CoV-2 infection were comparable, as well as cumulative incidences of clinically relevant RTI in both periods. Conclusion: Vaccination with BCG in the afternoon offered better protection against SARS-CoV-2 infections than BCG vaccination in the morning in the first six months after vaccination.

Routine vaccination for influenza and pneumococcal disease and its effect on COVID-19 in a population of Dutch older adults.

Objectives: Protective heterologous beneficial effects of vaccines have been reported, and in this study we aimed to assess the impact of routine pneumococcal and influenza vaccination on the incidence and symptom duration of COVID-19 in a population of Dutch older adults. Methods: This cohort study is a secondary analysis of the BCG-CORONA-ELDERLY study, a randomised controlled trial on the effect of BCG vaccination on the cumulative incidence of respiratory tract infections requiring medical intervention in adults ≥60 years. The primary outcome was the cumulative incidence of a self-reported positive SARS-CoV-2 PCR test, and was assessed using a Fine-Gray competing risks model adjusted for baseline characteristics at enrolment. We analysed data from November 1st 2020 until the end of the main study in May 2021. Results: Routine vaccination data 2020/2021 were available for 1963/2014 (97.5 %) participants; 44/1963 (2.2 %) were excluded due to COVID-19 before vaccination. 1076/1919 (56.1 %) had received the influenza vaccine and 289/1919 (15.1 %) the pneumococcal vaccine. The cumulative incidence of COVID-19 was 0.030 (95 %CI 0.021-0.041) in those vaccinated against influenza compared to 0.029 (95 %CI 0.019-0.041) in the unvaccinated group (subdistribution hazard ratio (SDHR) 1.018; 95 %CI 0.602-1.721). For pneumococcal vaccination the cumulative incidence was 0.031 (95 %CI 0.015-0.056) for the vaccinated and 0.029 (95 %CI 0.022-0.038) for non-vaccinated individuals (SDHR 0.961; 95 %CI 0.443-2.085). BCG vaccination in the previous year and sex were not significant effect modifiers in the primary analysis. Duration of fever, cough and dyspnoea was also not significantly different between treatment arms. Conclusion: Neither influenza nor pneumococcal vaccination was associated with a lower incidence or shorter duration of COVID-19 symptoms in older adults.

Corrigendum: The impact of circadian rhythm on Bacillus Calmette-Guérin vaccination effects on SARS-CoV-2 infections.

[This corrects the article DOI: 10.3389/fimmu.2023.980711.].

The impact of Bacillus Calmette-Guérin vaccination on antibody response after COVID-19 vaccination.

Earlier studies showed that BCG vaccination improves antibody responses of subsequent vaccinations. Similarly, in older volunteers we found an increased IgG receptor-binding domain (RBD) concentration after SARS-CoV-2 infection if they were recently vaccinated with BCG. This study aims to assess the effect of BCG on the serum antibody concentrations induced by COVID-19 vaccination in a population of adults older than 60 years. Serum was collected from 1,555 participants of the BCG-CORONA-ELDERLY trial a year after BCG or placebo, and we analyzed the anti-SARS-CoV-2 antibody concentrations using a fluorescent-microsphere-based multiplex immunoassay. Individuals who received the full primary COVID-19 vaccination series before serum collection and did not test positive for SARS-CoV-2 between inclusion and serum collection were included in analyses (n = 945). We found that BCG vaccination before first COVID-19 vaccine (median 347 days [IQR 329-359]) did not significantly impact the IgG RBD concentration after COVID-19 vaccination in an older European population.

Timing and sequence of vaccination against COVID-19 and influenza (TACTIC): a single-blind, placebo-controlled randomized clinical trial.

Background: Novel mRNA-based vaccines have been used to protect against SARS-CoV-2, especially in vulnerable populations who also receive an annual influenza vaccination. The TACTIC study investigated potential immune interference between the mRNA COVID-19 booster vaccine and the quadrivalent influenza vaccine, and determined if concurrent administration would have effects on safety or immunogenicity. Methods: TACTIC was a single-blind, placebo-controlled randomized clinical trial conducted at the Radboud University Medical Centre, the Netherlands. Individuals ≥60 years, fully vaccinated against COVID-19 were eligible for participation and randomized into one of four study groups: 1) 0.5 ml influenza vaccination Vaxigrip Tetra followed by 0.3 ml BNT162b2 COVID-19 booster vaccination 21 days later, (2) COVID-19 booster vaccination followed by influenza vaccination, (3) influenza vaccination concurrent with the COVID-19 booster vaccination, and (4) COVID-19 booster vaccination only (reference group). Primary outcome was the geometric mean concentration (GMC) of IgG against the spike (S)-protein of the SARS-CoV-2 virus, 21 days after booster vaccination. We performed a non-inferiority analysis of concurrent administration compared to booster vaccines alone with a predefined non-inferiority margin of -0.3 on the log10-scale. Findings: 154 individuals participated from October, 4, 2021, until November, 5, 2021. Anti-S IgG GMCs for the co-administration and reference group were 1684 BAU/ml and 2435 BAU/ml, respectively. Concurrent vaccination did not meet the criteria for non-inferiority (estimate -0.1791, 95% CI -0.3680 to -0.009831) and antibodies showed significantly lower neutralization capacity compared to the reference group. Reported side-effects were mild and did not differ between study groups. Interpretation: Concurrent administration of both vaccines is safe, but the quantitative and functional antibody responses were marginally lower compared to booster vaccination alone. Lower protection against COVID-19 with concurrent administration of COVID-19 and influenza vaccination cannot be excluded, although additional larger studies would be required to confirm this. Trial registration number: EudraCT: 2021-002186-17. Funding: The study was supported by the ZonMw COVID-19 Programme.

Shifting the Immune Memory Paradigm: Trained Immunity in Viral Infections.

Trained immunity is defined as the de facto memory characteristics induced in innate immune cells after exposure to microbial stimuli after infections or certain types of vaccines. Through epigenetic and metabolic reprogramming of innate immune cells after exposure to these stimuli, trained immunity induces an enhanced nonspecific protection by improving the inflammatory response upon restimulation with the same or different pathogens. Recent studies have increasingly shown that trained immunity can, on the one hand, be induced by exposure to viruses; on the other hand, when induced, it can also provide protection against heterologous viral infections. In this review we explore current knowledge on trained immunity and its relevance for viral infections, as well as its possible future uses.

ACTIVATE-2: A Double-Blind Randomized Trial of BCG Vaccination Against COVID-19 in Individuals at Risk.

In a recent study of our group with the acronym ACTIVATE, Bacillus Calmete-Guérin (BCG) vaccination reduced the occurrence of new infections compared to placebo vaccination in the elderly. Most benefit was found for respiratory infections. The ACTIVATE-2 study was launched to assess the efficacy of BCG vaccination against coronavirus disease 2019 (COVID-19). In this multicenter, double-blind trial, 301 volunteers aged 50 years or older were randomized (1:1) to be vaccinated with BCG or placebo. The trial end points were the incidence of COVID-19 and the presence of anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) antibodies, which were both evaluated through 6 months after study intervention. Results revealed 68% relative reduction of the risk to develop COVID-19, using clinical criteria or/and laboratory diagnosis, in the group of BCG vaccine recipients compared with placebo-vaccinated controls, during a 6-month follow-up (OR 0.32, 95% CI 0.13-0.79). In total, eight patients were in need of hospitalization for COVID-19: six in the placebo group and two in the BCG group. Three months after study intervention, positive anti-SARS-CoV-2 antibodies were noted in 1.3% of volunteers in the placebo group and in 4.7% of participants in BCG-vaccinated group. These data indicate that BCG vaccination confers some protection against possible COVID-19 among patients older than 50 years with comorbidities. BCG vaccination may be a promising approach against the COVID-19 pandemic.

Corrigendum: ACTIVATE-2: A double-blind randomized trial of BCG vaccination against COVID-19 in individuals at risk.

[This corrects the article DOI: 10.3389/fimmu.2022.873067.].

Bacillus Calmette-Guérin vaccine to reduce healthcare worker absenteeism in COVID-19 pandemic, a randomized controlled trial.

OBJECTIVES: The COVID-19 pandemic increases healthcare worker (HCW) absenteeism. The bacillus Calmette-Guérin (BCG) vaccine may provide non-specific protection against respiratory infections through enhancement of trained immunity. We investigated the impact of BCG vaccination on HCW absenteeism during the COVID-19 pandemic. METHODS: HCWs exposed to COVID-19 patients in nine Dutch hospitals were randomized to BCG vaccine or placebo in a 1:1 ratio, and followed for one year using a mobile phone application. The primary endpoint was the self-reported number of days of unplanned absenteeism for any reason. Secondary endpoints included documented COVID-19, acute respiratory symptoms or fever. This was an investigator-funded study, registered at ClinicalTrials.gov (NCT03987919). RESULTS: In March/April 2020, 1511 HCWs were enrolled. The median duration of follow-up was 357 person-days (interquartile range [IQR], 351 to 361). Unplanned absenteeism for any reason was observed in 2.8% of planned working days in the BCG group and 2.7% in the placebo group (adjusted relative risk 0.94; 95% credible interval, 0.78-1.15). Cumulative incidences of documented COVID-19 were 14.2% in the BCG and 15.2% in the placebo group (adjusted hazard ratio (aHR) 0.94; 95% confidence interval (CI), 0.72-1.24). First episodes of self-reported acute respiratory symptoms or fever occurred in 490 (66.2%) and 443 (60.2%) participants, respectively (aHR: 1.13; 95% CI, 0.99-1.28). Thirty-one serious adverse events were reported (13 after BCG, 18 after placebo), none considered related to study medication. CONCLUSIONS: During the COVID-19 pandemic, BCG-vaccination of HCW exposed to COVID-19 patients did not reduce unplanned absenteeism nor documented COVID-19.

Correction to: Two Randomized Controlled Trials of Bacillus Calmette-Guérin Vaccination to reduce absenteeism among health care workers and hospital admission by elderly persons during the COVID-19 pandemic: A structured summary of the study protocols for two randomised controlled trials.

An amendment to this paper has been published and can be accessed via the original article.

Two Randomized Controlled Trials of Bacillus Calmette-Guérin Vaccination to reduce absenteeism among health care workers and hospital admission by elderly persons during the COVID-19 pandemic: A structured summary of the study protocols for two randomised controlled trials.

OBJECTIVES: The objectives of these two separate trials are: (1) to reduce health care workers (HCWs) absenteeism; and (2) to reduce hospital admission among the elderly during the COVID-19 pandemic through BCG vaccination. TRIAL DESIGN: Two separate multi-centre placebo-controlled parallel group randomized trials PARTICIPANTS: (1) Health care personnel working in the hospital or ambulance service where they will take care of patients with the COVID-19 infection and (2) elderly ≥60 years. The HCW trial is being undertaken in 9 hospitals. The elderly trial is being undertaken in locations in the community in Nijmegen, Utrecht, and Veghel, in the Netherlands, using senior citizen organisations to facilitate recruitment. INTERVENTION AND COMPARATOR: For both trials the intervention group will be randomized to vaccination with 0.1 ml of the licensed BCG vaccine (Danish strain 1331, SSI, Denmark, equivalent to 0.075 mg attenuated M. bovis). The placebo group consists of 0.1 ml 0.9% NaCl, which is the same amount, and has the same colour and appearance as the suspended BCG vaccine. MAIN OUTCOMES: (1) Number of days of unplanned work absenteeism in HCWs for any reason which can be continuously measured on a bi-weekly basis, and (2) the cumulative incidence of hospital admission due to documented COVID-19. RANDOMISATION: Participants will be randomized to BCG vaccine or placebo (1;1) centrally using a computer- based system, stratified by study centre. BLINDING (MASKING): Subjects, investigators, physicians and outcome assessors are blinded for the intervention. Only the pharmacist assistant that prepares- and research personnel that administers- study medicines are unblinded. NUMBERS TO BE RANDOMISED (SAMPLE SIZE): (1) The sample size for the first trial is N=1500 HCWs randomised 1:1 to either BCG vaccine (n=750) and placebo (n=750) and (2) The sample size for the second trial is N=1600 elderly persons randomised to BCG vaccine (n=800) and the placebo group (n=800). TRIAL STATUS: HCW: version 4.0, 24-04-2020. Recruitment began 25-03-2020 and was completed on the 23-04-2020. Elderly: version 3.0, 04-04-2020. Recruitment began 16-04- 2020 and is ongoing. TRIAL REGISTRATION: The HCWs trial was registered 31-03-2020 at clinicaltrials.gov (identifier: NCT04328441) and registered 20-03-2020 at the Dutch Trial Registry (trialregister.nl, identifier Trial NL8477). The elderly trial was registered 22-04-2020 at the Dutch trial registry with number NL8547. FULL PROTOCOL: The full protocols will be attached as additional files, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol.

Safety and COVID-19 Symptoms in Individuals Recently Vaccinated with BCG: a Retrospective Cohort Study.

Bacille Calmette-Guérin (BCG) induces long-term boosting of innate immunity, termed trained immunity, and decreases susceptibility to respiratory tract infections. BCG vaccination trials for reducing SARS-CoV-2 infection are underway, but concerns have been raised regarding the potential harm of strong innate immune responses. To investigate the safety of BCG vaccination, we retrospectively assessed coronavirus disease 2019 (COVID-19) and related symptoms in three cohorts of healthy volunteers who either received BCG in the last 5 years or did not. BCG vaccination is not associated with increased incidence of symptoms during the COVID-19 outbreak in the Netherlands. Our data suggest that BCG vaccination might be associated with a decrease in the incidence of sickness during the COVID-19 pandemic (adjusted odds ratio [AOR] 0.58, p < 0.05), and lower incidence of extreme fatigue. In conclusion, recent BCG vaccination is safe, and large randomized trials are needed to reveal if BCG reduces the incidence and/or severity of SARS-CoV-2 infection.