BCG scarring and improved child survival: a combined analysis of studies of BCG scarring

"Glycans in Trained Immunity: Educators of innate immune memory in homeostasis and disease"

Trained Immunity is defined as a biological process normally induced by exogenous or endogenous insults that triggers epigenetic and metabolic reprogramming events associated with long-term adaptation of innate immune cells. This trained phenotype confers enhanced responsiveness to subsequent triggers, resulting in an innate immune "memory" effect. Trained Immunity, in the past decade, has revealed important benefits for host defense and homeostasis, but can also induce potentially harmful outcomes associated with chronic inflammatory disorders or autoimmune diseases. Interestingly, evidence suggest that the "trainers" prompting trained immunity are frequently glycans structures. In fact, the exposure of different types of glycans at the surface of pathogens is a key driver of the training phenotype, leading to the reprogramming of innate immune cells through the recognition of those glycan-triggers by a variety of glycan-binding proteins (GBPs) expressed by the immune cells. β-glucan or mannose-enriched structures in Candida albicans are some of the examples that highlight the potential of glycans in trained immunity, both in homeostasis and in disease. In this review, we will discuss the relevance of glycans exposed by pathogens in establishing key immunological hubs with glycan-recognizing receptors expressed in immune cells, highlighting how this glycan-GBP network can impact trained immunity. Finally, we discuss the power of glycans and GBPs as potential targets in trained immunity, envisioning potential therapeutic applications.

The mark of success: The role of vaccine-induced skin scar formation for BCG and smallpox vaccine-associated clinical benefits

Skin scar formation following Bacille Calmette-Guérin (BCG) or smallpox (Vaccinia) vaccination is an established marker of successful vaccination and 'vaccine take'. Potent pathogen-specific (tuberculosis; smallpox) and pathogen-agnostic (protection from diseases unrelated to the intentionally targeted pathogen) effects of BCG and smallpox vaccines hold significant translational potential. Yet despite their use for centuries, how scar formation occurs and how local skin-based events relate to systemic effects that allow these two vaccines to deliver powerful health promoting effects has not yet been determined. We review here what is known about the events occurring in the skin and place this knowledge in the context of the overall impact of these two vaccines on human health with a particular focus on maternal-child health.

The association between BCG scars and self-reported chronic diseases: A cross-sectional observational study within an RCT of Danish health care workers

INTRODUCTION

The live-attenuated vaccines Bacillus Calmette-Guérin (BCG) and Vaccinia have been associated with beneficial non-specific effects. We assessed the prevalence of BCG and Vaccinia vaccine scars in a cohort of Danish health care workers and investigated the association between the presence of vaccine scars and self-reported chronic diseases.

METHODS

Cross-sectional study utilizing baseline data collected during 2020-2021 at enrollment in a BCG trial aiming to assess the effect of BCG vaccination on absenteeism and infectious disease morbidity during the SARS-COV-2 pandemic. In Denmark, Vaccinia was discontinued in 1977, and BCG was phased out in the early 1980s. We used logistic regression analysis (adjusted for sex, birth year, and smoking status) to estimate the association between scar status and chronic diseases, providing adjusted Odds Ratios (aORs) with 95 % Confidence Intervals, for participants born before 1977, and born from 1965 to 1976.

RESULTS

The cohort consisted of 1218 participants (206 males; 1012 females) with a median age of 47 years (Q1-Q3: 36-56). Among participants born 1965-1976 (n = 403), who experienced the phase-outs, having BCG and/or Vaccinia scar(s) vs. having no vaccine scars yielded an aOR of 0.51 (0.29-0.90) of self-reported chronic disease; an effect primarily driven by BCG. In the same birth cohort, having vaccine scar(s) was most strongly associated with a lower prevalence of chronic respiratory and allergic diseases; the aORs being 0.39 (0.16-0.97) and 0.39 (0.16-0.91), respectively.

CONCLUSION

Having a BCG scar was associated with a lower prevalence of self-reported chronic disease.

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.

Multi-omics analysis of innate and adaptive responses to BCG vaccination reveals epigenetic cell states that predict trained immunity

Immune responses are tightly regulated yet highly variable between individuals. To investigate human population variation of trained immunity, we immunized healthy individuals with Bacillus Calmette-Guérin (BCG). This live-attenuated vaccine induces not only an adaptive immune response against tuberculosis but also triggers innate immune activation and memory that are indicative of trained immunity. We established personal immune profiles and chromatin accessibility maps over a 90-day time course of BCG vaccination in 323 individuals. Our analysis uncovered genetic and epigenetic predictors of baseline immunity and immune response. BCG vaccination enhanced the innate immune response specifically in individuals with a dormant immune state at baseline, rather than providing a general boost of innate immunity. This study advances our understanding of BCG's heterologous immune-stimulatory effects and trained immunity in humans. Furthermore, it highlights the value of epigenetic cell states for connecting immune function with genotype and the environment.

Using real-life data to model the impact of increasing BCG vaccination coverage and scar prevalence on all-cause infant mortality

PURPOSE

Estimating the potential impact on infant mortality of increasing Bacille Calmette-Guérin (BCG) vaccination coverage and BCG scar prevalence.

METHODS

Guinea-Bissau Health and Demographic Surveillance System data on BCG vaccination coverage, scar status, and all-cause mortality were used for this study. Mortality risk (MR) by scar status was assessed in Cox models providing adjusted mortality rate ratios (aMRRs). Distributions were fitted for survival, vaccination coverage, and scar prevalence. Models for 12-month mortality were calculated. We utilized World Bank data on birth rates and mortality rates to assess the potential global impact of optimizing BCG vaccination programs.

RESULTS

BCG coverage was 81% and scar prevalence 42% among 2-month-old infants, and the 1- to 12-month scar/no scar aMRR was 0.40 (0.22, 0.76). Modeling 2-month 99% vaccination coverage with 95% developing scars would change the 1- to 12-month MR by -8% (-21%, +12%). Globally, the reduction in the MR between 1- and 12-month would be -14% (-14%, -15%), corresponding to -208,075 (-214,453, -204,023) fewer infant deaths/year.

CONCLUSIONS

We confirmed previous observations: having a BCG scar markedly reduces infant MR. Increasing current global 2-month BCG vaccination coverage from 76% to 99%, and scar prevalence among vaccinated infants from 52% to 95% might reduce global infant mortality by >200,000 deaths/year. Thus, optimizing BCG vaccination programs to focus on increasing early BCG vaccination coverage and the overall scar prevalence would have major public health benefits.

Evolution of the Bacillus Calmette-Guérin scar Russia and Moreau strains in newborns: A brazilian cohort

Background

In Brazil, in 1925, the Moreau strain was introduced, and since its implementation, it has been the routine vaccine for health services. Since 2013, many countries, including Brazil, have been experiencing problems with the production of vaccines. As of January 2018, the country started to use the BCG vaccine with Russia strain, developed by the Serum Institute India.

Objective

To describe the evolution of the vaccine scar in neonates vaccinated by BCG-Russia compared to BCG-Moreau.

Methods

This was a cohort study was conducted in Salvador city, northeast Brazil. The study population consisted of newborns from the reference maternity hospital, who were vaccinated with BCG-ID strains Moreau or Russia, followed up to assess vaccine lesion evolution.

Results

It was observed that regardless of the vaccine strains, the evolution of the lesion was the same: wheal, reddish macula, induration, pustule, ulcer, and scar. The proportion of vaccine scar in the group vaccinated with BCG Russia was lower than that of BCG Moreau, 62.5 % and 90.9 %, respectively, with a statistically significant difference.

Conclusion

The evolution of the scar by BCG-Russia was similar to the Moreau scar, however different proportions were observed in different stages of lesion between the groups.

Immunogenicity of Bacillus Calmette-Guérin in pigs: potential as a translational model of non-specific effects of BCG

Background

Clinical and immunological studies in humans show that the live attenuated Bacillus Calmette-Guérin (BCG) vaccine has beneficial non-specific effects, increasing resistance against diseases other than tuberculosis. The underlying mechanisms are currently being explored. The pig exhibits considerable physiological similarity to humans in anatomy and physiology, suggesting that similar responses to BCG could be expected. Studies of the non-specific effects of BCG in pigs are scarce. We investigated the feasibility of using pigs as a large animal model to investigate the non-specific immunological effects of BCG.

Methods

In a series of experiments, we randomized newborn or young piglets from conventional farms to receiving BCG or placebo and investigated the persistence of live BCG bacteria in various tissues, the immunogenicity of BCG in ex vivo blood and in vitro stimulation assays, and the acute phase protein and clinical responses to heterologous infectious challenge with influenza A virus or Actinobacillus pleuropneumoniae.

Results

The BCG vaccine was generally well tolerated. In contrast to humans, no skin reaction in the form of abscesses, ulcers, or scars was observed. Live BCG was recovered from draining lymph nodes in 2/13 animals 20 weeks after vaccination. Specific in vitro responses of IFN-γ to antigen-specific re-stimulation with mycobacterial antigen were increased but not TNF-responses to TLR2 or TLR4 agonists. A few genes were differentially expressed in blood after vaccination, including the antiviral genes RIG-I and CSF1, although the effect disappeared after correction for multiple testing. Clinical symptoms after heterologous bacterial or viral respiratory infections did not differ, nor did virus copies in nasopharyngeal samples after the challenge. However, the acute phase protein response was significantly reduced in BCG-vaccinated animals after influenza challenge but not after A. pleuropneumoniae challenge.

Discussion

BCG was safe in pigs, inducing specific immunological responses, but our model did not corroborate the innate immunological responsiveness to BCG seen in humans. The dose of BCG or the bacterial and viral challenges may have been sub-optimal. Even so, the acute phase protein response to influenza infection was significantly reduced in BCG-vaccinated animals.

Erratum: Factors influencing scar formation following Bacille Calmette-Guérin (BCG) vaccination

[This corrects the article DOI: 10.1016/j.heliyon.2023.e15241.].

Factors influencing scar formation following Bacille Calmette-Guérin (BCG) vaccination

The prevalence of scar formation following Bacille Calmette-Guérin (BCG) vaccination varies globally. The beneficial off-target effects of BCG are proposed to be stronger amongst children who develop a BCG scar. Within an international randomised trial ('BCG vaccination to reduce the impact of coronavirus disease 2019 (COVID-19) in healthcare workers'; BRACE Trial), this nested prospective cohort study assessed the prevalence of and factors influencing scar formation, as well as participant perception of BCG scarring 12 months following vaccination . Amongst 3071 BCG-recipients, 2341 (76%) developed a BCG scar. Scar prevalence was lowest in Spain and highest in UK. Absence of post-injection wheal (OR 0.4, 95%CI 0.2-0.9), BCG revaccination (OR 1.7, 95%CI 1.3-2.0), female sex (OR 2.0, 95%CI 1.7-2.4), older age (OR 0.4, 95%CI 0.4-0.5) and study country (Brazil OR 1.6, 95%CI 1.3-2.0) influenced BCG scar prevalence. Of the 2341 participants with a BCG scar, 1806 (77%) did not mind having the scar. Participants more likely to not mind were those in Brazil, males and those with a prior BCG vaccination history. The majority (96%) did not regret having the vaccine. Both vaccination-related (amenable to optimisation) and individual-related factors affected BCG scar prevalence 12 months following BCG vaccination of adults, with implications for maximising the effectiveness of BCG vaccination.

Beneficial non-specific effects of live vaccines against COVID-19 and other unrelated infections

Live attenuated vaccines could have beneficial, non-specific effects of protecting against vaccine-unrelated infections, such as BCG protecting against respiratory infection. During the COVID-19 pandemic, testing of these effects against COVID-19 was of interest to the pandemic control programme. Non-specific effects occur due to the broad effects of specific live attenuated vaccines on the host immune system, relying on heterologous lymphocyte responses and induction of trained immunity. Knowledge of non-specific effects has been developed in randomised controlled trials and observational studies with children, but examining of whether the same principles apply to adults and older adults was of interest to researchers during the pandemic. In this Personal View, we aim to define a framework for the analysis of non-specific effects of live attenuated vaccines against vaccine-unrelated infections with pandemic potential using several important concepts. First, study endpoints should prioritise severity of infection and overall patient health rather than incidence of infection only (eg, although several trials found no protection of the BCG vaccine against COVID-19 infection, it is associated with lower overall mortality than placebo). Second, revaccination of an individual with the same live attenuated vaccine could be the most effective strategy against vaccine-unrelated infections. Third, coadministration of several live attenuated vaccines might enhance beneficial non-specific effects. Fourth, the sequence of vaccine administration matters; the live attenuated vaccine should be the last vaccine administered before exposure to the pandemic infection and non-live vaccines should not be administered afterwards. Fifth, live attenuated vaccines could modify the immune response to specific COVID-19 vaccines. Finally, non-specific effects of live attenuated vaccines should always be analysed with subgroup analysis by sex of individuals receiving the vaccines.

Prevalence and risk factors of latent tuberculosis infection among college students: a systematic review and meta-analysis

OBJECTIVES

College students are at increased risk of tuberculosis (TB), which increases their likelihood of developing latent tuberculosis infections (LTBI). This study aimed to estimate the pooled prevalence of LTBI and identify its risk factors.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

We searched PubMed, Embase, Scopus, Web of Science, CNKI, Wanfang and CBM databases (10 March 2022) for studies published in any language. The pooled prevalence of LTBI was estimated using random effects methods. Factors associated with LTBI were evaluated by determining standardised mean difference (SMD) with 95% confidence interval (CI). All analyses were performed using the Stata 15.1.

RESULTS

A total of 50 studies from 18 countries were included, with 44 tuberculin skin test (n = 623,732) and 19 interferon gamma release assay (n = 38,266) estimates. The prevalence of a positive tuberculin skin test was 20% (95% CI: 17-23%), and the prevalence of a positive interferon gamma release assay was 9% (95% CI: 7%-11%) among college students. Older age (SMD: 1.67, 95% CI: 1.31-2.13), no Bacillus Calmette-Guérin vaccination/scar (SMD: 1.51, 95% CI: 1.06-2.16), contact with TB cases (SMD: 1.34, 95% CI: 1.11-1.62), clinical training (SMD: 1.93, 95% CI: 1.65-2.26) and overweight/obesity (SMD: 1.17, 95% CI: 1.06-1.30) were associated with a higher prevalence of LTBI. Sex was not associated with LTBI prevalence.

CONCLUSION

College students have an increased risk of LTBI, although it varies by geographical area. This meta-analysis provides evidence of risk factors for LTBI in college students. Infection control measures should be conducted for college students with LTBI.

What's Old and New in Tuberculosis Vaccines for Children

Tuberculosis (TB) is a leading cause of global child mortality. Until the turn of the 21st century, Mycobacterium bovis bacille Calmette-Guerin (BCG) was the only vaccine to prevent TB. The pediatric TB vaccine pipeline has advanced in the past decade to include the evaluation of novel whole cell vaccines to replace infant BCG and investigation of subunit and whole cell vaccines to boost TB immunity during adolescence. We describe the history of BCG, current TB vaccine candidates in clinical trials, and the challenges and opportunities for future TB vaccine research in children. Children are a critical target population for TB vaccines, and expansion of the pediatric TB vaccine pipeline is urgently needed to end the TB pandemic.

Neonatal Bacillus Calmette-Guérin Vaccination to Prevent Early-Life Eczema: A Systematic Review and Meta-analysis

ABSTRACT

Increasing evidence suggests that early-life bacillus Calmette-Guérin (BCG) vaccine could prevent atopic eczema through its beneficial off-target effects. In this meta-analysis, 3 randomized control trials with similar methods were included and enabled robust estimations with low heterogeneity, involving a total of 5655 children randomized to early-life BCG Denmark (n = 2832) or no BCG (n = 2823). Meta-analyses suggest a beneficial effect of BCG to prevent eczema (risk ratio [RR], 0.89; 95% confidence interval [CI], 0.82-0.98). In subgroup analyses, BCG was more beneficial in boys (RR, 0.84; 95% CI, 0.74-0.95) and in children born to 2 atopic parents (RR, 0.81; 95% CI, 0.68-0.97). The NNT to prevent one case of eczema among children of 1 or 2 atopic parent was 20 (95% CI, 12-50). Bacillus Calmette-Guérin Denmark leads to an 11% reduction in the risk of eczema in early life. A greater effect was observed with increasing predisposition. Given its well-established safety profile, neonatal BCG vaccination should be considered for children of atopic parents.

Que reste-t-il du BCG 100 ans après ?

Le BCG a fêté ses 100 ans en juillet 2021, en pleine pandémie de COVID-19, alors qu'une baisse des prises en charge de cas de tuberculose avait lieu suite à la diminution des activités de dépistage à travers le monde. Si le développement vaccinal permet d'envisager un vaccin plus efficace et mieux toléré que le BCG, on peut retenir que celui-ci réduit, lorsqu'il est administré dans l'enfance, le risque de tuberculose maladie mais aussi de mortalité toute cause, notamment dans les pays à faibles revenus. Son impact chez l'adulte reste moins évident. Cependant, l'effet protecteur observé vis-à-vis d'autres pathogènes (pressenti par Calmette lui-même) a conduit à évaluer l'efficacité de la revaccination par le BCG à l’âge adulte.

Correlation between innate and adaptive immunity response in TB children post BCG vaccination. Is it effective or not?: Cross-sectional study

Background

How far the role of innate immunity and adaptive immunity do in children who have been BCG vaccinated in controlling the course and the severity of the TB disease has not been completely known. Mycobacterium tuberculosis entry to the body will be recognized by Toll-like receptors found on macrophages, neutrophils, and dendritic cells as part of the innate immune response, after which the dendritic cells will then present the antigen to lymphocyte T0 cells and initiate the adaptive immune response (of which CD4 T cells have an important role in). Was one or were both of these immune responses function well or not in a BCG Vaccinated Children with TB?

Objective

This study aim to find a better understanding of the role of innate immune response assessed by TLR2/TLR4 mRNA gene expression and serum TLR2/TLR4 levels, while the role of adaptive immune response is assessed by analyzing serum CD4 level in children with TB who have had BCG vaccination.

Methods

This cross-sectional study was conducted among children with TB at the outpatient and inpatient wards at Bhakti Medicare and Jakarta Islamic Hospital. Expression of mRNA gene was measured using the Boom method and protein serum levels were measured using the ELISA method. The results were analyzed by using the SPSS v.23 program.

Results

Sixty-nine children were recruited as subjects. In this study, 68.1% of whom had BCG scars. TLR4 mRNA gene expression was found to be higher than TLR2 mRNA gene expression. Serum CD4 level was found to be highest out of TLR2 and TLR4 level, but serum TLR2 level was higher than TLR4 level. TLR2/TLR4 mRNA gene expression, serum TLR2/TLR4 levels, and CD4 levels in subjects with BCG scar were also found to be significantly higher than in subjects without BCG scar (p < 0.001). There was a significant positive correlation between TLR2/TLR4 mRNA gene expression and serum TLR2/TLR4 levels (r = 0.860; r = 0.864; p < 0.001) and between serum levels TLR2/TLR4 with serum CD4 levels (r = 0.822; r = 0.832 p < 0.001).

Conclusion

As early as possible, BCG vaccine administration is needed in endemic countries, but it must be ensured that scars can be formed. It is also important to control Latent TB Infection (LTBI) to prevent transmission and relapse of disease.

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For the prevention of TB disease, it is important to understand the innate and adaptive immune responses according BCG scar.

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Mycobacterium tuberculosis recognition by TLR as the innate immune response followed by the adaptive immune response by CD4 cells.

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There is a strong positive correlation between the expression of mRNA gene and the concentration of TLR and CD4 in BCG-vaccinated subjects.

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BCG vaccination should be done as early as possible in endemic countries, as it provides better protection against TB infection.

Mortality risk among frail neonates might be associated with maternal BCG scar status: Observational study from Guinea-Bissau

BACKGROUND

Maternal priming with Bacille Calmette-Guérin (BCG) has been associated with reduced offspring mortality. We investigated this association in a cohort of frail neonates.

METHODS

We performed an observational study within a randomized BCG trial conducted at the Neonatal Intensive Care Unit (NICU) in Guinea-Bissau from 2015-2017. At NICU admission and following informed consent, the maternal scar status was evaluated by visual inspection before neonates were randomized 1:1 to receive BCG + Oral Polio Vaccine (OPV) immediately versus BCG + OPV at hospital discharge. Stratified by maternal scar status, we assessed overall in-hospital and post-discharge mortality up to 42 days of age in Cox Proportional Hazards models providing adjusted Mortality Rate Ratios (aMRRs).

RESULTS

62% (903/1451) of mothers had a BCG scar. During NICU admission, the mortality risk was 1.7% (15/903) for neonates born to mothers with a scar vs 3.3% (18/548) for those born to mothers with no scar, the maternal scar/no scar aMRR = 0.53 (0.26-1.05); the aMRR was 0.39 (0.13-1.05) for unvaccinated neonates and 0.70 (0.26-1.87) for vaccinated neonates.

CONCLUSION

This small study indicates that maternal BCG might be associated with reduced all-cause NICU mortality. If confirmed elsewhere, this finding would have substantial ramifications for global health.

The Structure of Mental Elasticity Education for Children in Plight Using Deep Learning

The purpose is to solve the problem that the current research on the impact of the microstructure of mental elasticity and its constituent factors on the development of the mental elasticity of children is not comprehensive, and the traditional artificial analysis method of mental problems has strong subjectivity and low accuracy. First, the structural equation model is used to study the microstructure of poor children's mental elasticity, and to explore the structural relationship and functional path between the mental elasticity of children and the self-efficacy of their mental health, psychological anxiety, and attachment. Second, a prediction model of mental problems of children in plight based on the backpropagation neural network (BPNN) is constructed. Finally, middle schools in the representative areas of Northwest China are selected as the research unit. The relevant research data are collected by issuing questionnaires, and the data set is constructed to verify the performance of the model. The experimental results show that the average prediction errors of the BPNN model and the support vector regression (SVR) model are 1.87 and 5.4, respectively. The error of BPNN is 65.4% lower than that of SVR, so BPNN has a better performance. The prediction results of the test set show that the actual error and the relative error of the BPNN model are controlled in the range of 0.01, and the prediction accuracy is high. The structural equation model has a high fitting degree. The results of the questionnaire analysis show that attachment, self-efficacy, and psychological anxiety exert a significant direct impact on mental elasticity. This exploration aims to conduct a micro investigation on the relationship among the three core variables (attachment, self-efficacy, and mental health) in the resilience research of children in plight, and analyze their resilience, to provide a theoretical basis for the resilience intervention design of vulnerable groups.

Photochemically-Mediated Inflammation and Cross-Presentation of Mycobacterium bovis BCG Proteins Stimulates Strong CD4 and CD8 T-Cell Responses in Mice

Conventional vaccines are very efficient in the prevention of bacterial infections caused by extracellular pathogens due to effective stimulation of pathogen-specific antibodies. In contrast, considering that intracellular surveillance by antibodies is not possible, they are typically less effective in preventing or treating infections caused by intracellular pathogens such as Mycobacterium tuberculosis. The objective of the current study was to use so-called photochemical internalization (PCI) to deliver a live bacterial vaccine to the cytosol of antigen-presenting cells (APCs) for the purpose of stimulating major histocompatibility complex (MHC) I-restricted CD8 T-cell responses. For this purpose, Mycobacterium bovis BCG (BCG) was combined with the photosensitiser tetraphenyl chlorine disulfonate (TPCS2a) and injected intradermally into mice. TPCS2a was then activated by illumination of the injection site with light of defined energy. Antigen-specific CD4 and CD8 T-cell responses were monitored in blood, spleen, and lymph nodes at different time points thereafter using flow cytometry, ELISA and ELISPOT. Finally, APCs were infected and PCI-treated in vitro for analysis of their activation of T cells in vitro or in vivo after autologous vaccination of mice. Combination of BCG with PCI induced stronger BCG-specific CD4 and CD8 T-cell responses than treatment with BCG only or with BCG and TPCS2a without light. The overall T-cell responses were multifunctional as characterized by the production of IFN-γ, TNF-α, IL-2 and IL-17. Importantly, PCI induced cross-presentation of BCG proteins for stimulation of antigen-specific CD8 T-cells that were particularly producing IFN-γ and TNF-α. PCI further facilitated antigen presentation by causing up-regulation of MHC and co-stimulatory proteins on the surface of APCs as well as their production of TNF-α and IL-1β in vivo. Furthermore, PCI-based vaccination also caused local inflammation at the site of vaccination, showing strong infiltration of immune cells, which could contribute to the stimulation of antigen-specific immune responses. This study is the first to demonstrate that a live microbial vaccine can be combined with a photochemical compound and light for cross presentation of antigens to CD8 T cells. Moreover, the results revealed that PCI treatment strongly improved the immunogenicity of M. bovis BCG.

Triple jeopardy in ageing: COVID-19, co-morbidities and inflamm-ageing

Covid-19 endangers lives, has disrupted normal life, changed the way medicine is practised and is likely to alter our world for the foreseeable future. Almost two years on since the presumptive first diagnosis of COVID-19 in China, more than two hundred and fifty million cases have been confirmed and more than five million people have died globally, with the figures rising daily. One of the most striking aspects of COVID-19 illness is the marked difference in individuals' experiences of the disease. Some, most often younger groups, are asymptomatic, whereas others become severely ill with acute respiratory distress syndrome (ARDS), pneumonia or proceed to fatal organ disease. The highest death rates are in the older and oldest age groups and in people with co-morbidities such as diabetes, heart disease and obesity. Three major questions seem important to consider. What do we understand about changes in the immune system that might contribute to the older person's risk of developing severe COVID-19? What factors contribute to the higher morbidity and mortality in older people with COVID-19? How could immunocompetence in the older and the frailest individuals and populations be supported and enhanced to give protection from serious COVID-19 illness?

Does maternal BCG prime for enhanced beneficial effects of neonatal BCG in the offspring?

OBJECTIVES

Bacille Calmette-Guérin (BCG) vaccination lowers the risk of severe infection; we tested whether effects are modulated by maternal BCG in a large cohort of BCG-vaccinated newborns from Guinea-Bissau.

METHODS

Maternal BCG scar status were inspected at enrolment in a BCG trial conducted from 2014-17 in Bissau, Guinea-Bissau. We tested associations with background factors for potential confounding; maternal age affected effect estimates >5% and accordingly, all analyses were adjusted for maternal age. Hospitalization data was collected prospectively and assessed in Cox-models providing adjusted Incidence Rate Ratios (aIRRs). In-hospital risk of death (case-fatality) risk was assessed using binomial regression providing adjusted Risk Ratios (aRRs).

RESULTS

60% (6,309/10,598) of mothers had a scar. The maternal-scar/no-scar admission aIRR was 0.96 (0.81-1.14) from 0-6 weeks and 1.12 (0.97-1.28) for 6 weeks-3 years. The 6-week in-hospital case-fatality infection aRR was 0.59 (0.34-1.05); 0.40 (0.17-0.91) for males and 0.86 (0.38-1.94) for females. Protection was especially evident against sepsis, the overall 6-week aRR=0.49 (0.26-0.91); no effect was observed for non-infectious deaths or after 6 weeks of age. Effects were similar across BCG strains and multivariate models adjusted for socioeconomic status did not affect estimates.

CONCLUSION

Among BCG-vaccinated newborns, there was a trend for fewer in-hospital deaths from infection associated with maternal BCG priming, especially for males. Providing BCG to adults without a vaccination scar might enhance their offspring's capacity to handle severe infections.

COVID-19 and Beyond: Exploring Public Health Benefits from Non-Specific Effects of BCG Vaccination

Bacille Calmette–Guérin (BCG) vaccination, widely used throughout the world to protect against infant tuberculous meningitis and miliary tuberculosis (TB), can provide broad non-specific protection against infectious respiratory diseases in certain groups. Interest in BCG has seen a resurgence within the scientific community as the mechanisms for non-specific protection have begun to be elucidated. The impact of the COVID-19 pandemic on nearly every aspect of society has profoundly illustrated the pressure that respiratory infections can place on a national healthcare system, further renewing interest in BCG vaccination as a public health policy to reduce the burden of those illnesses. However, the United States does not recommend BCG vaccination due to its variable effectiveness against adult TB, the relatively low risk of Mycobacterium tuberculosis infection in most of the United States, and the vaccine’s interference with tuberculin skin test reactivity that complicates TB screening. In this review, we explore the broad immune training effects of BCG vaccination and literature on the effects of BCG vaccination on COVID-19 spread, disease severity, and mortality. We further discuss barriers to scheduled BCG vaccination in the United States and how those barriers could potentially be overcome.

Comparison TLR2 and TLR4 serum levels in children with pulmonary and extrapulmonary tuberculosis with and without a Bacillus Calmette-Guérin (BCG) scar

The formation of a scar after Mycobacterium bovis Bacillus Calmette-Guérin (BCG) vaccination influences the effectiveness of protection against Mycobacterium tuberculosis (MTB) infection. The innate immunity plays a critical role both in the pathophysiology of tuberculosis (TB) and BCG vaccination protection mechanism. Parts of innate immunity: macrophages, dendritic cells, and neutrophils, have microbial recognition surface receptors called Toll-like receptors (TLR) 2 and 4. The objective of this study is to compare the serum levels of TLR2 and TLR4 in BCG-vaccinated pediatric patients with pulmonary and extrapulmonary TB. This cross-sectional study included children aged less than 18 years old with contracted TB disease and had received BCG vaccination. The subjects were recruited by convenience sampling from both outpatient and inpatient care at Bhakti Medicare and Jakarta Islamic Hospital, from November 2018 to December 2019. Serum TLR2 and TLR4 levels measured using ELISA of the two groups of subjects: children with pulmonary TB (PTB) and extrapulmonary TB (EPTB), were then compared. The presence of BCG scars was included in the analysis. Independent T-test, ANOVA test, and Kolmogorov-Smirnov normality tests on the SPSS program were used to statistically analyze the results. Serum TLR2 and TLR4 levels were higher in EPTB group, but the difference was not significant (TLR2 p = 0.758 and TLR4 p = 0.646, respectively). Subjects with BCG scars in both groups have significantly higher serum TLR2 and TLR4 levels than those without BCG scars in the EPTB group (EPTB p = 0.001 and p = 0.004, respectively); (PTB p < 0.001 and p < 0.001, respectively). BCG vaccination and MTB infection stimulate better innate immune response in EPTB than in PTB and serum TLR2 and TLR4 levels in those with BCG scars were higher when compared to those without BCG scars.

100 years of Mycobacterium bovis bacille Calmette-Guérin

Mycobacterium bovis bacille Calmette-Guérin (BCG), an experimental vaccine designed to protect cattle from bovine tuberculosis, was administered for the first time to a newborn baby in Paris in 1921. Over the past century, BCG has saved tens of millions of lives and has been given to more humans than any other vaccine. It remains the sole tuberculosis vaccine licensed for use in humans. BCG provides long-lasting strong protection against miliary and meningeal tuberculosis in children, but it is less effective for the prevention of pulmonary tuberculosis, especially in adults. Evidence mainly from the past two decades suggests that BCG has non-specific benefits against non-tuberculous infections in newborn babies and in older adults, and offers immunotherapeutic benefit in certain malignancies such as non-muscle invasive bladder cancer. However, as a live attenuated vaccine, BCG can cause localised or disseminated infections in immunocompromised hosts, which can also occur following intravesical installation of BCG for the treatment of bladder cancer. The legacy of BCG includes fundamental discoveries about tuberculosis-specific and non-specific immunity and the demonstration that tuberculosis is a vaccine-preventable disease, providing a foundation for new vaccines to hasten tuberculosis elimination.

Parental Bacillus Calmette-Guérin vaccine scars decrease infant mortality in the first six weeks of life: A retrospective cohort study

BACKGROUND

Live attenuated vaccines have been observed to have particularly beneficial effects for child survival when given in the presence of maternally transferred immunity (priming). We aimed to test this finding and furthermore explore the role of paternal priming.

METHODS

In an exploratory, retrospective cohort study in 2017, parental Bacillus Calmette-Guérin (BCG) scars were assessed for infants from the Bandim Health Project (BHP) who had participated in a 2008-2013 trial of neonatal BCG vaccination. Parental scar effects on mortality were estimated from birth to 42 days, the age of the scheduled diphtheria-tetanus-pertussis (DTP) vaccination, in Cox proportional hazard models adjusted with Inverse Probability of Treatment Weighting.

FINDINGS

For 66% (510/772) of main trial infants that were still registered in the BHP area, at least one parent was located. BCG scar prevalence was 77% (353/461) among mothers and 63% (137/219) among fathers. In the first six weeks of life, maternal scars were associated with a mortality reduction of 60% (95%CI, 4% to 83%) and paternal scars with 49% (-68% to 84%). The maternal scar association was most beneficial among infants that had received BCG vaccination at birth (73% (-1% to 93%)). Although priming was less evident for paternal scars, having two parents with scars reduced mortality by 89% (13% to 99%) compared with either one or none of the parents having a scar.

INTERPRETATION

Parental BCG scars were associated with strongly increased early-life survival. These findings underline the importance of future studies into the subject of inherited non-specific immunity and parental priming.

FUNDING

Danish National Research Foundation; European Research Council; Novo Nordisk Foundation; University of Southern Denmark.

Oral Polio Vaccine to Protect Against COVID-19: Out of the Box Strategies?

The global coronavirus disease 2019 pandemic has raised significant concerns of developing rapid, broad strategies to protect the vulnerable population and prevent morbidity and mortality. However, even with an aggressive approach, controlling the pandemic has been challenging, with concerns of emerging variants that likely escape vaccines, nonadherence of social distancing/preventive measures by the public, and challenges in rapid implementation of a global vaccination program that involves mass production, distribution, and execution. In this review, we revisit the utilization of attenuated vaccinations, such as the oral polio vaccine, which are safe, easy to administer, and likely provide cross-protection against respiratory pathogens. We discuss the rationale and data supporting its use and detail description of available vaccines that could be repurposed for curtailing the pandemic.

Neonatal Bacille Calmette-Guérin vaccination and tuberculin skin test reactions at 2- and 6-months: Effects on mortality up to 1 year of age

BACKGROUND

In randomized trials, Bacille Calmette-Guérin (BCG) vaccine has been associated with reduced all-cause mortality. BCG-induced Tuberculin Skin Test (TST) reactions have also been associated with reduced all-cause mortality. We aimed to assess the association between TST responses and subsequent mortality in three birth cohorts and conducted a meta-analysis of existing studies.

METHODS

Observational study within three Guinea-Bissau BCG trial birth cohorts (conducted 2002-04, 2009-2013 and 2014-18) that encompassed children who were BCG-vaccinated within 28 days with TSTs performed at 2- (n = 1389) and 6-months (n = 2635) of age. We evaluated TST reaction determinants by binomial regression and assessed the association between TSTs > 1 mm (reactors) vs. ≤ 1 mm (non-reactors) and subsequent mortality risk up to age 12 months in Cox-models providing Mortality Rate Ratios (MRRs). We searched PubMed for studies to calculate meta-estimates of the association between TST reactivity by age 2- and 6-months and all-cause mortality.

RESULTS

Large post-vaccination wheal size was associated with 6-month TST positivity and so was receiving BCG-Denmark or BCG-Japan, compared with BCG-Russia. By age 2 months, 22% (302/1389) of infants were TST reactors with a 2-12-month mortality risk of 1.7% (5/302) vs. 3.3% (36/1087) for non-reactors, the corresponding reactor/non-reactor MRR = 0.49 (0.19-1.26). By age 6 months, 44% (1149/2635) of infants were reactors and the 6-12-month mortality risk was 0.4% (4/1149) vs. 0.6% (9/1486) for non-reactors, the MRR = 0.87 (0.27-2.86). The literature search provided 3 studies. The meta-analysis revealed a uniform pattern of reduced mortality associated with TST reactivity, a TST response by 2 months being associated with an MRR of 0.59 (0.39-0.90); for 6-month TST responses the MRR was 0.65 (0.43-1.00).

CONCLUSION

Among BCG-vaccinated infants, TST reactions were associated with markedly reduced mortality. Improved vaccination technique and using certain BCG strains could lead to a higher TST reaction prevalence, which would enhance BCG's beneficial non-specific effects.

Prevalence of Latent TB and Effectiveness of BCG Vaccination Against Latent Tuberculosis: An Observational Study

OBJECTIVES

This study aimed to determine the prevalence of latent tuberculosis infection (LTBI) in immigrant children and adolescents (aged 0-17 years) living or recently arriving in Sweden. It also aimed to estimate the effectiveness of Bacillus Calmette-Guérin (BCG) against LTBI in immigrant children coming to Sweden from high-incidence countries, most of them being asylum seekers. LTBI was defined as a positive Quantiferon or a tuberculin skin test (TST) of ≥ 10 mm in small children from whom it was difficult to obtain 3 mL of blood.

DESIGN

A typical BCG scar was used as a substitute for written documentation of BCG vaccination. The study comprised 1,404 immigrants aged 0-17 years. The arms and legs of all of them were inspected for a BCG scar, and Quantiferon or TST was performed. The study was a retrospective, observational, comparative cohort study.

RESULTS

LTBI was found in 123 of 1,011 (12%) children with a BCG scar and in 116 of 393 (29.5%) without a BCG scar, giving an estimated vaccine effectiveness of 59%.

CONCLUSIONS

LTBI was common among the immigrant children (17%). LTBI can progress to active TB and then spread in the immigrant population and to the general population if all immigrant arrivals are not tested and given prophylactic treatment if they have LTBI. The BCG vaccine was found to have a significant effect on LTBI (59%).

BCG skin reactions by 2 months of age are associated with better survival in infancy: a prospective observational study from Guinea-Bissau

Introduction

Receiving Bacille Calmette-Guérin (BCG)-Denmark vaccine at birth has been associated with ~40% reductions in all-cause neonatal mortality. We evaluated determinants of BCG skin reaction characteristics by age 2 months and tested the association with subsequent mortality.

Methods

Prospective observational study amalgamating five trials providing BCG-at-birth that were conducted between 2002 and 2018 in Guinea-Bissau. The reaction status and size were evaluated at home-visits by 2 months of age among 6012 neonates; mortality from 2 to 12 months was assessed at subsequent visits. Reaction determinants were evaluated by binomial regression providing risk ratios (RRs). In Cox-models providing adjusted mortality rate ratios (aMRRs), we assessed the association between (1) having a 2-month reaction (yes/no) and (2) reaction size tertiles and subsequent all-cause mortality risk. A subgroup had their BCG reaction evaluated and were bled at age 4 weeks; their samples underwent in vitro analysis for specific and non-specific cytokine responses.

Results

The BCG strain was the main determinant for developing a 2-month reaction and the reaction size: the BCG-Russia/BCG-Denmark RR for large-reaction was 0.38 (0.30–0.47) and the BCG-Russia/BCG-Japan RR was 0.61 (0.51–0.72). 5804 infants (96.5%) were reactors by age 2 months; 208 (3.5%) were non-reactors. The 2–12 months mortality risk was 4.8% (10/208) for non-reactors, 2.9% (64/2213) for small reactors, 1.8% (30/1710) for medium reactors and 0.8% (15/1881) for large reactors. The reactor/non-reactor aMRR was 0.49 (0.26–0.95) and there was a linear trend of decreasing mortality with increasing reaction size (p for trend <0.001). BCG reactors had higher 4-week specific and non-specific cytokine responses, responses that were highest among those with large reactions.

Conclusion

Among BCG-vaccinated infants, having a BCG skin reaction by age 2 months was associated with markedly better survival, as was the reaction size. Our findings thus support that BCG has substantial effects on all-cause mortality. Emphasising at-birth vaccination with immunogenic BCG strains and revaccinating non-reactors and small reactors could have major public health benefits.

Trial registration numbers

NCT00146302, NCT00168610, NCT00625482, NCT01989026 and NCT02447536.

The introduction of BCG vaccination to neonates in Northern Sweden, 1927-31: Re-analysis of historical data to understand the lower mortality among BCG-vaccinated children

BACKGROUND

Following the introduction of oral Bacille Calmette-Guérin (BCG) a century ago, Albert Calmette suggested that BCG both provided protection against death from tuberculosis (TB) and other causes. The findings were not pursued. Today, there is considerable evidence that intradermal BCG have beneficial non-specific effects (NSEs). We re-analyzed data from BCG's introduction 1927-1931 in Sweden hypothesizing that BCG reduced infectious deaths.

METHODS

In three papers published by Dr Carl Näslund, the progress of oral neonatal BCG rollout provided free-of-charge and the effects on child mortality in the highly TB-prevalent region Norrbotten was sequentially updated. We analyzed cause-specific post-neonatal mortality by vaccination status excluding deaths from congenital conditions. Due to apparent differences in effects during study years, effects were assessed overall and separately in two periods (1927-1929, 1930-1931).

RESULTS

According to Näslund, TB households were slightly more likely to accept vaccination; fewer newborns that were sick or had congenital problems were vaccinated. BCG coverage was 28.3% (5659/20,012); 8.7% (1746/20,012) died. The BCG/unvaccinated Risk Ratio (RR) of post-neonatal childhood death was 0.53 (0.45-0.62). BCG was associated with 80% (49-92%) reduced mortality from TB. From 1927 to 29, BCG appeared to protect strongly against deaths from all diseases, including the non-infectious, RR = 0.09 (0.02-0.36), presumably reflecting selection bias. From 1930 to 1931, there was no protection against non-infectious deaths, RR = 0.92 (0.49-1.70) indicating less bias (p = 0.004 for same effect). During 1930-1931, BCG was associated with reductions in non-TB infectious deaths (RR = 0.75 (0.58-0.97)); 2/3 were caused by respiratory infections, against which the BCG/unvaccinated RR was 0.61 (0.43-0.84). Other causes of death were less frequent and provided no clear pattern, except that BCG was associated with more meningitis deaths, RR = 6.85 (2.20-21.4).

CONCLUSION

Healthy vaccinee bias, particularly in 1927-1929, resulted in strongly beneficial overall BCG effects. However, the 1930-1931 data provided some support that BCG both protected against TB deaths and deaths from respiratory infections.

Immediate Bacille Calmette-Guérin vaccination to neonates requiring perinatal treatment at the maternity ward in Guinea-Bissau: A randomized controlled trial

BACKGROUND

Randomized controlled trials (RCTs) indicate that Bacille Calmette-Guérin (BCG) vaccination provides broad beneficial non-specific protection against infections. We investigated the effect on in-hospital mortality of providing BCG immediately upon admission to a neonatal intensive care unit (NICU), rather than BCG-at-discharge. The pre-trial NICU mortality was 13% and we hypothesized that BCG would reduce mortality by 40%.

METHODS

Parallel-group, open-label RCT initiated in 2013 in Guinea-Bissau. NICU-admitted neonates were randomized 1:1 to BCG+Oral Polio Vaccine (OPV) immediately (intervention) versus BCG+OPV at hospital discharge (control; usual practice). The trial was discontinued due to decreasing in-hospital mortality and major NICU restructuring. We assessed overall and disease-specific mortality by randomization allocation in Cox Proportional Hazards models providing Mortality Rate Ratios (MRRs).

RESULTS

We recruited 3,353 neonates and the overall mortality was 3.1% (52/1676) for BCG-vaccinated neonates versus 3.3% (55/1677) for controls, MRR=0.94 (0.64-1.36). For non-infectious causes of death the MRR was 1.20 (0.70-2.07) and there tended to be fewer deaths from infections in the BCG group (N=14) than among controls (N=21), MRR=0.65 (0.33-1.28).

CONCLUSIONS

Providing BCG+OPV to frail neonates was safe and might protect against fatal infection in the immediate newborn period. Deaths due to prematurity and perinatal complications were unaffected by BCG.

Determinants of Bacille Calmette-Guérin scarification in Danish children

Background

Studies in low-income countries have shown that among Bacille Calmette-Guérin (BCG) vaccinated children, those who develop a BCG-scar have significantly better survival than those who do not develop a scar. In a Danish multicenter randomized clinical trial we assessed determinants for developing a BCG-scar and for BCG scar size following neonatal BCG vaccination.

Methods

At three Danish hospitals, newborns were randomized 1:1 to BCG vaccination or no BCG vaccination. The infants were invited for a clinical examination at the ages of 3 and 13 months. At 13 months, the scar site was inspected and scar size measured. We investigated three groups of determinants; external, parental, and individual-level determinants on relative scar prevalence and differences in median scar sizes.

Results

Among 2118 BCG vaccinated infants, 2039 (96 %) were examined at 13 months; 1857 of these (91 %) had developed a BCG-scar. Compared with Copenhagen University Hospital, Hvidovre (85 %), Copenhagen University Hospital, Rigshospitalet had a scar prevalence of 95 % (adjusted Prevalence ratio (aPR) = 1.24 [CI 95 %: 1.18 to 1.30]); it was 93 % at Kolding Hospital (aPR 1.27 [CI 95 %: 1.19 to 1.35]). Increasing vaccine experience was positively associated with developing a scar and with scar size.

Conclusion

Across multiple potential determinants of BCG scaring and size, logistical factors dominated. The results support that injection technique is an important determinant of developing a scar. Given the strong link between having a BCG scar and subsequent health, improved BCG vaccination technique could play a major role for child health.

Postneonatal under-5 mortality in peri-urban and rural Eastern Uganda, 2005-2015

INTRODUCTION

Community and individual sociodemographic characteristics play an important role in child survival. However, a question remains how urbanisation and demographic changes in sub-Saharan Africa affect community-level determinants for child survival.

METHODS

Longitudinal data from the Iganga/Mayuge Health and Demographic Surveillance Site was used to obtain postneonatal under-5 mortality rates between March 2005 and February 2015 in periurban and rural areas separately. Multilevel survival analysis models were used to identify factors associated with mortality.

RESULTS

There were 43 043 postneonatal under-5 children contributing to 116 385 person years of observation, among whom 1737 died. Average annual crude mortality incidence rate (IR) differed significantly between periurban and rural areas (9.0 (8.1 to 10.0) per 1000 person-years vs 18.1 (17.1 to 19.0), respectively). In periurban areas, there was evidence for decreasing mortality from IR=11.3 (7.7 to 16.6) in 2006 to IR=4.5 (3.0 to 6.9) in 2015. The mortality fluctuated with no evidence for reduction in rural areas (IR=19.0 (15.8 to 22.8) in 2006; IR=15.5 (13.0 to 18.6) in 2015). BCG vaccination was associated with reduced mortality in periurban and rural areas (adjusted rate ratio (aRR)=0.45; 95% CI 0.30 to 0.67 and aRR=0.56; 95% CI 0.41 to 0.76, respectively). Maternal education level within the community was associated with reduced mortality in both periurban and rural sites (aRR=0.83; 95% CI 0.70 to 0.99; aRR=0.90; 95% CI 0.81 to 0.99). The proportion of households in the poorest quintile within the community was associated with mortality in rural areas only (aRR=1.08; 95% CI 1.00 to 1.18). In rural areas, a large disparity existed between the least poor and the poorest (aRR=0.50; 95% CI 0.27 to 0.92).

CONCLUSION

We found evidence for a mortality decline in peri-urban but not rural areas. Investments in the known key health (eg, vaccination) and socio-economic interventions (education, and economic development) continue to be crucial for mortality declines. Focused strategies to eliminate the disparity between wealth quintiles are also warranted. There may be equitable access to health services in peri-urban areas but improved metrics of socioeconomic position suitable for peri-urban residents may be needed.

On the relationship between BCG coverage and national COVID-19 outcome: could 'heterologous' herd immunity explain why some countries are better off?

The COVID-19 pandemic has affected most parts of the global society since its emergence, and the scientific community has been challenged with questions urgently demanding answers. One of the early hypotheses on COVID-19 outcome was that some protection could be offered by the tuberculosis vaccine (BCG), and several clinical studies were initiated along with the emergence of numerous observational studies on the relationship between BCG and COVID-19 severity. In the present work, I demonstrate a strong correlation between the number of years that countries implemented BCG vaccination plans and age-standardized mortality rates during the first months of the pandemic in Europe. Further analyses of age groups in two European countries with comparably few confounding factors and easily identifiable groups of BCG-vaccinated and non-vaccinated subgroups suggest a population-level effect of BCG on national outcomes of COVID-19. This phenomenon of 'heterologous herd immunity' deserves further investigation, both in epidemiological and experimental studies.