Intravesical Bacille Calmette-Guerin (BCG) Vaccine Affects Cognition.

The Montreal Cognitive Assessment (MoCA) is a valuable assessment of the patient's awareness of time and place. We show that bacille Calmette-Guerin (BCG) significantly affects MoCA testing when administered by the intravesical route. MoCA scores were lower with increasing age and higher in more formally educated individuals. Patients receiving BCG tended to maintain their MoCA scores, whereas almost half the control cases tended to show reduced scores. This benefit is supported by reduced pre-amyloid biomarkers in BCG-injected healthy volunteers and a favorable effect on neuronal dendritic development in animal models. Our results suggest that BCG has a beneficial impact on the cognitive status of older individuals.

Bacille Calmette-Guérin vaccination to prevent febrile and respiratory illness in adults (BRACE): secondary outcomes of a randomised controlled phase 3 trial.

Background: Bacille Calmette-Guérin (BCG) vaccination has off-target (non-specific) effects that are associated with protection against unrelated infections and decreased all-cause mortality in infants. We aimed to determine whether BCG vaccination prevents febrile and respiratory infections in adults. Methods: This randomised controlled phase 3 trial was done in 36 healthcare centres in Australia, Brazil, the Netherlands, Spain, and the United Kingdom. Healthcare workers were randomised to receive BCG-Denmark (single 0.1 ml intradermal injection) or no BCG in a 1:1 ratio using a web-based procedure, stratified by stage, site, age, and presence of co-morbidity. The difference in occurrence of febrile or respiratory illness were measured over 12 months (prespecified secondary outcome) using the intention-to-treat (ITT) population. This trial is registered with ClinicalTrials.gov, NCT04327206. Findings: Between March 30, 2020, and April 1, 2021, 6828 healthcare workers were randomised to BCG-Denmark (n = 3417) or control (n = 3411; no intervention or placebo) groups. The 12-month adjusted estimated risk of ≥1 episode of febrile or respiratory illness was 66.8% in the BCG group (95% CI 65.3%-68.2%), compared with 63.4% in the control group (95% CI 61.8%-65.0%), a difference of +3.4 percentage points (95% CI +1.3% to +5.5%; p 0.002). The adjusted estimated risk of a severe episode (defined as being incapacitated for ≥3 consecutive days or hospitalised) was 19.4% in the BCG group (95% CI 18.0%-20.7%), compared with 18.8% in the control group (95% CI 17.4%-20.2%) a difference of +0.6 percentage points (95% CI -1.3% to +2.5%; p 0.6). Both groups had a similar number of episodes of illness, pneumonia, and hospitalisation. There were three deaths, all in the control group. There were no safety concerns following BCG vaccination. Interpretation: In contrast to the beneficial off-target effects reported following neonatal BCG in infants, a small increased risk of symptomatic febrile or respiratory illness was observed in the 12 months following BCG vaccination in adults. There was no evidence of a difference in the risk of severe disease. Funding: Bill & Melinda Gates Foundation, Minderoo Foundation, Sarah and Lachlan Murdoch, the Royal Children's Hospital Foundation, Health Services Union NSW, the Peter Sowerby Foundation, SA Health, the Insurance Advisernet Foundation, the NAB Foundation, the Calvert-Jones Foundation, the Modara Pines Charitable Foundation, the UHG Foundation Pty Ltd, Epworth Healthcare, the National Health and Medical Research Council, the Swiss National Science Foundation and individual donors.

Childhood vaccination trends during 2019 to 2022 in Tanzania and the impact of the COVID-19 pandemic.

The COVID-19 pandemic has significantly disrupted healthcare systems at all levels globally, notably affecting routine healthcare services, such as childhood vaccination. This study examined the impact of these disruptions on routine childhood vaccination programmes in Tanzania. We conducted a longitudinal study over four years in five Tanzanian regions: Mwanza, Dar es Salaam, Mtwara, Arusha, and Dodoma. This study analyzed the trends in the use of six essential vaccines: Bacille Calmette-Guérin (BCG), bivalent Oral Polio Vaccine (bOPV), Diphtheria Tetanus Pertussis, Hepatitis-B and Hib (DTP-HepB-Hib), measles-rubella (MR), Pneumococcal Conjugate Vaccine (PCV), and Rota vaccines. We evaluated annual and monthly vaccination trends using time-series and regression analyses. Predictive modeling was performed using an autoregressive integrated moving average (ARIMA) model. A total of 32,602,734 vaccination events were recorded across the regions from 2019 to 2022. Despite declining vaccination rates in 2020, there was a notable rebound in 2021, indicating the resilience of Tanzania's immunization program. The analysis also highlighted regional differences in vaccination rates when standardized per 1000 people. Seasonal fluctuations were observed in monthly vaccination rates, with BCG showing the most stable trend. Predictive modeling of BCG indicated stable and increasing vaccination coverage by 2023. These findings underscore the robustness of Tanzania's childhood immunization infrastructure in overcoming the challenges posed by the COVID-19 pandemic, as indicated by the strong recovery of vaccination rates post-2020. We provide valuable insights into the dynamics of vaccination during a global health crisis and highlight the importance of sustained immunization efforts to maintain public health.

Maternal BCG scars and mortality risk for male and female newborns: observational study from Guinea-Bissau.

BACKGROUND: Maternal priming with Bacille Calmette-Guérin (BCG) has been associated with reduced mortality in male offspring. We investigated this association in a cohort of healthy BCG-vaccinated neonates. METHODS: Observational study within a randomized controlled trial comparing different BCG strains conducted in Guinea-Bissau from 2017-2020. As part of trial inclusion procedures, on the day of discharge from the maternity ward, maternal BCG scar status was evaluated by visual inspection, followed by offspring BCG and polio vaccination. Through mortality data collected at telephone interviews at six weeks and six months of age, we assessed all-cause mortality risk in Cox Proportional Hazards models adjusted for maternal schooling and BCG strain, providing adjusted Mortality Rate Ratios (aMRRs). RESULTS: 64% (11,070/17,275) of mothers had a BCG scar, which for females and overall was not associated with neither admission risk, admission severity nor all-cause mortality. By six months of age, the mortality rate (MR) was 4.1 (200 deaths/4,919 person-years) for the maternal BCG scar cohort and 5.2 (139 deaths/2,661 person-years) for no maternal scar, aMRR=0.86 (0.69-1.06). In males, six-month MRs were 4.3 (109/2,531) for maternal BCG scar vs 6.3 (87/1,376) for no scar, the maternal scar/no scar aMRR being 0.74 (0.56-0.99). In females, six-month MRs were 3.8 (91/2,388) vs 4.0 (52(1,286), the aMRR being 1.04 (0.74-1.47), p for interaction with sex=0.16. CONCLUSION: While we cannot rule out an association in females, being born to a mother with a BCG scar reduced the risk of death during early infancy for BCG-vaccinated males, reproducing findings from previous studies.

Chest wall tumor following intravesical BCG instillation for non-muscle invasive bladder cancer.

Mycobacterium bovis bacille Calmette-Guérin (BCG) is the most effective intravesical immunotherapy for non-muscle invasive bladder cancer (NMIBC), administered after its transurethral resection. Although its instillation is generally well tolerated, BCG-related infectious complications may occur in up to 5% of patients. Clinical manifestations may arise in conjunction with initial BCG instillation or develop months or years after the last BCG instillation. The range of presentations and potential severity pose an imminent challenge for clinicians. We present a case of an isolated subcutaneous chest wall abscess in an immunocompetent 52-year-old patient nearly two years after intravesical BCG instillation for NMIBC, an absolute rarity. As the enlarging chest wall tumor may be misinterpreted as malignancy, its expedient diagnosis and prompt treatment are of critical importance.

Multidisciplinary consensus document on the current treatment of bacille Calmette-Guérin-unresponsive non-muscle invasive bladder tumor.

Radical cystectomy is the current treatment of choice for patients with BCG-unresponsive non-muscle invasive bladder tumor (NMIBC). However, the high comorbidity of this surgery and its effects on the quality of life of patients require the investigation and implementation of bladder-sparing treatment options. These must be evaluated individually by the uro-oncology committee based on the characteristics of the BCG failure, type of tumor, patient preferences and treatment options available in each center. Based on FDA-required oncologic outcomes (6-month complete response rate for CIS: 50%; duration of response in responders for CIS and papillary: 30% at 12 months and 25% at 18 months), there is not currently a strong preference for one treatment over another, although the intravesical route seems to offer less toxicity. This work summarizes the evidence on the management of BCG-unresponsive NMIBC based on current scientific evidence and provides consensus recommendations on the most appropriate treatment.

The Applications of ELISpot in the Identification and Treatment of Various Forms of Tuberculosis and in the Cancer Immunotherapies.

ELISpot (enzyme-linked immunospot) is a powerful immunological tool for the detection of cytokine-secreting cells at a single-cell resolution. It is widely used for the diagnosis of various infectious diseases, e.g., tuberculosis and sarcoidosis, and it is also widely used in cancer immunotherapy research. Its ability to distinguish between active and latent forms of tuberculosis makes it an extremely powerful tool for epidemiological studies and contact tracing. In addition to that, it is a very useful tool for the research and development of cancer immunotherapies. ELISpot can be employed to assess the immune responses against various tumor-associated antigens, which could provide valuable insights for the development of effective therapies against cancers. Furthermore, it plays a crucial role to the evaluation of immune responses against specific antigens that not only could aid in vaccine development but also assist in treatment monitoring and development of therapeutic and diagnostic strategies. This chapter briefly describes some of the applications of ELISpot in tuberculosis and cancer research.

Effects of Neonatal BCG-Japan Versus BCG-Russia Vaccination on Overall Mortality and Morbidity: Randomized Controlled Trial From Guinea-Bissau (BCGSTRAIN II).

Background: Vaccination with the Danish strain of bacille Calmette-Guérin (BCG) has been associated with pronounced reductions in all-cause neonatal mortality and morbidity. Developing a skin reaction postvaccination is associated with markedly reduced mortality risk. It is unknown whether the beneficial nonspecific effects are maintained across different BCG strains. Methods: This was an open-label randomized controlled trial in Guinea-Bissau, comparing BCG-Japan (n = 8754) versus BCG-Russia (n = 8752) for all-cause hospital admission risk by 6 weeks of age (primary outcome) and 6 months of age. Additional secondary outcomes were in-hospital case-fatality risk (CFR), all-cause mortality, and BCG skin reaction prevalence. Participants were followed through telephone calls at 6 weeks and 6 months, with a subgroup also visited at home. We assessed admission and mortality risk in Cox models providing incidence rate ratios (IRRs) and mortality rate ratios. CFR and skin reactions were assessed by binomial regression providing risk ratios. Analyses were done overall and stratified by sex. Results: BCG strain was not associated with admission risk, the BCG-Japan/BCG-Russia IRR being 0.92 (95% confidence interval [CI], .81-1.05) by 6 weeks and 0.92 (95% CI, .82-1.02) by 6 months. By 6 months of age, there were significantly fewer BCG-Japan infants with no skin reaction (1%) than for BCG-Russia (2%), the risk ratio being 0.36 (95% CI, .16-.81). BCG-Japan skin reactions were also larger. Conclusions: Both vaccines induced a skin reaction in almost all participants. The BCG strains had comparable effects on morbidity and mortality, but BCG-Japan was associated with more and larger skin reactions that are indicators of lower mortality risk. Clinical Trials Registration: NCT03400878.

Autosomal Recessive IL-12p40 Deficiency due to a Mutation in the IL12B Gene: Report of a Brazilian Patient with Lymph Node Mycobacterial Infection.

Background: Autosomal recessive interleukin (IL)-12p40 deficiency is a genetic etiology of Mendelian susceptibility to mycobacterial disease (MSMD). It has been described in ∼50 patients, usually with onset at childhood with Bacille Calmette-Guérin (BCG) and Salmonella infections. Case Presentation: A male patient born to consanguineous parents was diagnosed with presumed lymph node MSMD at the age of 13 years after ocular symptoms. A positive history of inborn error of immunity was present: BCG reaction, skin abscess, and recurrent oral candidiasis. Abnormal measurements of cytokine levels, IL-12p40 and interferon-gamma (IFN-γ), lead to the diagnosis of MSMD. Genetic analysis showed a mutation in exon 7 of the IL12B gene. Currently, the patient is alive under prophylactic antibiotics. Conclusion: We report a rare case of IL-12p40 deficiency in a Latin American patient. Medical history was crucial for immune defect suspicion, as confirmed by precision diagnostic medicine tools.

Retrospective cohort study exploring the impact of universal Tuberculosis (TB) vaccination cessation on the epidemiology of paediatric TB in Ireland, 2011-2021.

BACKGROUND: Since 2010, Ireland's Tuberculosis (TB) crude incidence rate (CIR) remains below 10 per 100,000 population defining it as a low TB incidence country. Ireland maintained a universal BCG vaccination programme until its discontinuation in 2015 due to lack of vaccine supply. This study explores the impact of discontinuing a national universal BCG vaccination programme on the epidemiology of paediatric TB cases. METHODS: We retrospectively analysed TB notifications aged 0-6 years old reported to the Irish National TB Surveillance System between 2011 and 2021. Key epidemiological characteristics and temporal trends in TB age specific incidence rates (ASIRs) were compared between 0 and 6 year old cases born during a period of universal BCG vaccination (2007-2015) and 0-6 year old cases born after BCG vaccination ceased (2015-2021). RESULTS: No significant temporal trend was detected in the overall 0-6 year old ASIR by notification year during 2011-2021 (IRR:0.95; 0.86-1.1). However, the temporal trend for cases born during universal vaccination showed a significant decline (0.74; CIR: 0.62-0.89) while cases born after BCG vaccination ceased had a non-significant increase (1.2; CIR: 0.73-1.86). A significantly declining temporal trend was detected among cases born in Ireland during universal vaccination (IRR:0.73; 0.62-0.86), but no significant trend was detected in the cases born outside Ireland during universal vaccination (IRR:0.83; 0.53-1.31). No significant trend was detected in cases born after vaccination ceased in either cases born in Ireland (IRR:1.0; 0.60-1.65) or those born outside Ireland (IRR:0.64; 0.29-1.40). CONCLUSIONS: Universal BCG cessation has not yet directly impacted on TB cases among 0-6 year olds in Ireland. However, interruption of the previously declining temporal trend in this cohort during universal vaccination may be an early warning of a future increase. Paediatric TB cases remain an important cohort for timely surveillance to monitor trends in this primarily unvaccinated cohort to evaluate the long-term effects.

Vaccines and Dementia: Part II. Efficacy of BCG and Other Vaccines Against Dementia.

 There is growing awareness that infections may contribute to the development of senile dementia including Alzheimer's disease (AD), and that immunopotentiation is therefore a legitimate target in the management of diseases of the elderly including AD. In Part I of this work, we provided a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents, culminating in the development of the tuberculosis vaccine strain Bacille Calmette-Guérin (BCG) as a treatment for some types of cancer as well as a prophylactic against infections of the elderly such as pneumonia. In Part II, we critically review studies that BCG and other vaccines may offer a measure of protection against dementia development. Five studies to date have determined that intravesicular BCG administration, the standard of care for bladder cancer, is followed by a mean ∼45% reduction in subsequent AD development in these patients. Although this could potentially be ascribed to confounding factors, the finding that other routine vaccines such as against shingles (herpes zoster virus) and influenza (influenza A virus), among others, also offer a degree of protection against AD (mean 29% over multiple studies) underlines the plausibility that the protective effects are real. We highlight clinical trials that are planned or underway and discuss whether BCG could be replaced by key components of the mycobacterial cell wall such as muramyl dipeptide. We conclude that BCG and similar agents merit far wider consideration as prophylactic agents against dementia.

Vaccines and Dementia: Part I. Non-Specific Immune Boosting with BCG: History, Ligands, and Receptors.

Vaccines such as Bacille Calmette-Guérin (BCG) can apparently defer dementia onset with an efficacy better than all drugs known to date, as initially reported by Gofrit et al. (PLoS One14, e0224433), now confirmed by other studies. Understanding how and why is of immense importance because it could represent a sea-change in how we manage patients with mild cognitive impairment through to dementia. Given that infection and/or inflammation are likely to contribute to the development of dementias such as Alzheimer's disease (Part II of this work), we provide a historical and molecular background to how vaccines, adjuvants, and their component molecules can elicit broad-spectrum protective effects against diverse agents. We review early studies in which poxvirus, herpes virus, and tuberculosis (TB) infections afford cross-protection against unrelated pathogens, a concept known as 'trained immunity'. We then focus on the attenuated TB vaccine, BCG, that was introduced to protect against the causative agent of TB, Mycobacterium tuberculosis. We trace the development of BCG in the 1920 s through to the discovery, by Freund and McDermott in the 1940 s, that extracts of mycobacteria can themselves exert potent immunostimulating (adjuvant) activity; Freund's complete adjuvant based on mycobacteria remains the most potent immunopotentiator reported to date. We then discuss whether the beneficial effects of BCG require long-term persistence of live bacteria, before focusing on the specific mycobacterial molecules, notably muramyl dipeptides, that mediate immunopotentiation, as well as the receptors involved. Part II addresses evidence that immunopotentiation by BCG and other vaccines can protect against dementia development.

[Guillain-Barré syndrome caused by intravesical instillation of Bacillus Calmette-Guérin]. / Bacillus Calmette­Guérin intravesicalis instillációja által okozott Guillain­Barré-szindróma.

Introduction - Guillain-Barré syndrome (GBS) is an acute inflammatory demyelinating polyneuropathy. In the vast majority of patients, 1-4 weeks before the onset of GBS-related symptoms, an event such as upper respiratory tract or gastrointestinal tract infection, surgical intervention or vaccination is present. To the best of our knowledge, this is the first case of GBS that occurred after intravesical Bacillus Calmette-Guérin (BCG) therapy in the absence of tuberculosis or any other infection in the English literature.
Case report – A 65-year-old male patient, who had no systemic disorders except hypertension and coronary artery disease, underwent transurethral resection of a bladder tumour further to imaging studies investigating macroscopic haematuria. A pathologic examination revealed a non-muscle-invasive high-grade (pT1HG) transitional cell carcinoma. Immediately after the fourth cycle of intravesical BCG, which was administered 2 months after surgery, the patient experienced numbness and weakness in his lower and upper extremities, respectively. There were no signs or symptoms related to an acute cranial pathology or infectious disease. Nerve conduction studies, which were carried out on the 7th day after the onset of the neurologic symptoms, revealed a demyelinating sensorimotor polyneuropathy with mild secondary axonal damage in upper and lower limbs with a sural sparing pattern.
Conclusion - Without tuberculosis infection, GBS can occur secondary to increased immune response and antibodies triggered by intravesical BCG therapy. However, considering the worldwide use of BCG vaccination and thousands of intravesical BCG therapies, this is a very rare adverse effect. 

Molecular detection of pre-ribosomal RNAs of Mycobacterium bovis bacille Calmette-Guérin and Mycobacterium tuberculosis to enhance pre-clinical tuberculosis drug and vaccine development.

Efforts are underway globally to develop effective vaccines and drugs against M. tuberculosis (Mtb) to reduce the morbidity and mortality of tuberculosis. Improving detection of slow-growing mycobacteria could simplify and accelerate efficacy studies of vaccines and drugs in animal models and human clinical trials. Here, a real-time reverse transcription PCR (RT-PCR) assay was developed to detect pre-ribosomal RNA (pre-rRNA) of Mycobacterium bovis bacille Calmette-Guérin (BCG) and Mtb. This pre-rRNA biomarker is indicative of bacterial viability. In two different mouse models, the presence of pre-rRNA from BCG and Mtb in ex vivo tissues showed excellent agreement with slower culture-based colony-forming unit assays. The addition of a brief nutritional stimulation prior to molecular viability testing further differentiated viable but dormant mycobacteria from dead mycobacteria. This research has set the stage to evaluate pre-rRNA as a BCG and/or Mtb infection biomarker in future drug and vaccine clinical studies.

Axillary Lymph Node in Extra-Ocular Retinoblastoma - Benign or Malignant?

A 1-year-old male child presented with whitish discoloration of pupil of the left eye and swelling over the left axilla. A contrast-enhanced magnetic resonance imaging of the brain and orbits performed revealed left eye extra-ocular retinoblastoma. 18F-fluorodeoxyglucose positron emission tomography/computed tomography scan was done in this child as a part of baseline staging of retinoblastoma in an ongoing research project. The scan revealed left eye extra-ocular retinoblastoma along with calcified left axillary level I lymph node.

The safety of BCG revaccination in the context of COVID-19.

The bacille Calmette-Guérin (BCG) vaccine is administered in many countries as part of their vaccination schedules. Epidemiologic studies have suggested a possible benefit of this vaccine in the context of the COVID-19 pandemic and other respiratory infections. We aimed to assess the safety of this intervention in BCG-primed adults. Adult health care workers (n = 451) received a single intradermal application of the BCG vaccine (Tokyo 172 strain) in the deltoid region of the right arm. Follow-up (30 days) calls and clinical inspections were guided using a standardized data sheet to assess local and systemic reactions. Early local reactions were common at 24 h and 7 days, such as erythema (74.9%, 69.2%), induration (55.7%, 59%), a papule (53.4%, 47.7%), and edema (48.3%, 38.1). Local symptoms (pruritus 44.8%, heat 16.2%, and pain 34.8%) were less frequent at day 7. Late expected reactions (14 and 30 days) included the formation of crusts (39.6% and 63.9%), a pustule (36.6% and 17%), or ulcers (28.8% and 17.7%). Severe reactions were limited to subcutaneous abscesses (2%) and lymphadenitis (<1%).

An Oxygen Supply Strategy for Sonodynamic Therapy in Tuberculous Granuloma Lesions Using a Catalase-Loaded Nanoplatform.

Purpose: Tuberculosis (TB) is a chronic disease caused by Mycobacterium tuberculosis (MTB) that remains a major global health challenge. One of the main obstacles to effective treatment is the heterogeneous microenvironment of TB granulomas. This study aimed to investigate the potential of a hypoxic remission-based strategy to enhance the outcome of tuberculosis treatment when implemented in combination with ultrasound. Methods: A PLGA nanoparticle (LEV@CAT-NPs) loaded with levofloxacin (LEV) and catalase (CAT) was fabricated by a double emulsification method, and its physical characteristics, oxygen production capacity, drug release capacity, and biosafety were thoroughly investigated. The synergistic therapeutic effects of ultrasound (US)-mediated LEV@CAT-NPs were evaluated using an experimental mouse model of subcutaneous tuberculosis granuloma induced by Bacille Calmette-Guérin (BCG) as a substitute for MTB. Results: LEV@CAT-NPs exhibited excellent oxygen production capacity, biosafety, and biocompatibility. Histological analysis revealed that ultrasound-mediated LEV@CAT-NPs could effectively remove bacteria from tuberculous granulomas, significantly alleviate the hypoxia state, reduce the necrotic area and inflammatory cells within the granuloma, and increase the penetration of dyes in granuloma tissues. The combined treatment also reduced the serum levels of inflammatory cytokines (eg, TNF-α, IL-6, and IL-8), and significantly downregulated the expression of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). These results suggested that the synergistic treatment of ultrasound-mediated LEV@CAT-NPs effectively eradicated the bacterial infection and reversed the hypoxic microenvironment of tuberculous granulomas, further promoting tissue repair. Conclusion: This study provides a non-invasive and new avenue for treating refractory tuberculosis infections. The potential role of regulating hypoxia within infected lesions as a therapeutic target for infection deserves further exploration in future studies.

Immune interaction between SARS-CoV-2 and Mycobacterium tuberculosis.

SARS-CoV-2 and Mycobacterium tuberculosis (Mtb) are major infectious causes of death, with meta-analyses and population-based studies finding increased mortality in co-infected patients simultaneously diagnosed with COVID-19 and tuberculosis (TB). There is a need to understand the immune interaction between SARS-CoV-2 and Mtb which impacts poor outcomes for those co-infected. We performed a PubMed and preprint search using keywords [SARS-CoV-2] AND [tuberculosis] AND [Immune response], including publications after January 2020, excluding reviews or opinions. Abstracts were evaluated by authors for inclusion of data specifically investigating the innate and/or acquired immune responses to SARS-CoV-2 and Mtb in humans and animal models, immunopathological responses in co-infection and both trials and investigations of potential protection against SARS-CoV-2 by Bacille Calmette Guérin (BCG). Of the 248 articles identified, 39 were included. Incidence of co-infection is discussed, considering in areas with a high burden of TB, where reported co-infection is likely underestimated. We evaluated evidence of the clinical association between COVID-19 and TB, discuss differences and similarities in immune responses in humans and in murine studies, and the implications of co-infection. SARS-CoV-2 and Mtb have both been shown to modulate immune responses, particularly of monocytes, macrophages, neutrophils, and T cells. Co-infection may result in impaired immunity to SARS-CoV-2, with an exacerbated inflammatory response, while T cell responses to Mtb may be modulated by SARS-CoV-2. Furthermore, there has been no proven potential COVID-19 clinical benefit of BCG despite numerous large-scale clinical trials.

BCG mediated protection of the lung against experimental SARS-CoV-2 infection.

The observation of reduced COVID-19 incidence and severity in populations receiving neonatal intradermal BCG vaccination vaccine raised the question of whether BCG can induce non-specific protection against the SARS-CoV-2 (SCV2) virus. Subsequent epidemiologic studies and clinical trials have largely failed to support this hypothesis. Furthermore, in small animal model studies all investigators have failed to observe resistance to viral challenge in response to BCG immunization by the conventional and clinically acceptable intradermal or subcutaneous routes. Nevertheless, BCG administered by the intravenous (IV) route has been shown to strongly protect both hamsters and mice against SCV2 infection and disease. In this Perspective, we review the current data on the effects of BCG vaccination on resistance to COVID-19 as well as summarize recent work in rodent models on the mechanisms by which IV administered BCG promotes resistance to the virus and discuss the translational implications of these findings.