BCG Vaccination and All-Cause Neonatal Mortality

Specific and Nonspecific Effects of Influenza Vaccines

With the introduction of the influenza vaccine in the official immunization schedule of most countries, several data regarding the efficacy, tolerability, and safety of influenza immunization were collected worldwide. Interestingly, together with the confirmation that influenza vaccines are effective in reducing the incidence of influenza virus infection and the incidence and severity of influenza disease, epidemiological data have indicated that influenza immunization could be useful for controlling antimicrobial resistance (AMR) development. Knowledge of the reliability of these findings seems essential for precise quantification of the clinical relevance of influenza immunization. If definitively confirmed, these findings can have a relevant impact on influenza vaccine development and use. Moreover, they can be used to convince even the most recalcitrant health authorities of the need to extend influenza immunization to the entire population. In this narrative review, present knowledge regarding these particular aspects of influenza immunization is discussed. Literature analysis showed that the specific effects of influenza immunization are great enough per se to recommend systematic annual immunization of younger children, old people, and all individuals with severe chronic underlying diseases. Moreover, influenza immunization can significantly contribute to limiting the emergence of antimicrobial resistance. The problem of the possible nonspecific effects of influenza vaccines remains unsolved. The definition of their role as inducers of trained immunity seems essential not only to evaluate how much they play a role in the prevention of infectious diseases but also to evaluate whether they can be used to prevent and treat clinical conditions in which chronic inflammation and autoimmunity play a fundamental pathogenetic role.

Can earlier BCG-Japan and OPV vaccination reduce early infant mortality? A cluster-randomised trial in Guinea-Bissau

OBJECTIVE

To assess the effect of providing BCG and oral polio vaccine (OPV) at an early home visit after delivery.

DESIGN

Cluster-randomised trial, randomising 92 geographically defined clusters 1:1 to intervention/control arms.

SETTING

Bandim Health Project Health and Demographic Surveillance System, Guinea-Bissau.

PARTICIPANTS

2226 newborns enrolled between July 2016 and August 2019.

INTERVENTIONS

In both arms, newborns received a home visit within 72 hours after birth. In intervention clusters (n=46), BCG and OPV were provided at the home visit.

MAIN OUTCOME MEASURE

Rates of non-accidental mortality were compared in Cox proportional hazards models from (last of) day 1 or enrolment, until (first of) day 60 or registration of non-trial vaccines.

RESULTS

A total of 35 deaths (intervention: 7, control: 28) were registered during the trial. Providing BCG and OPV reduced non-accidental early infant mortality by 59% (8-82%). The intervention also reduced non-accidental hospital admissions. The intervention had little impact on growth and BCG scarring and tended to increase the risk of consultations.

CONCLUSIONS

The trial was stopped early due to lower-than-expected enrolment and event rates when 33% of the planned number of newborns had been enrolled. Despite the small size of the trial, the results support that early BCG and OPV vaccinations are beneficial and reduce early child mortality and morbidity.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Registry (NCT02504203).

Implications of Non-Specific Effects for Testing, Approving, and Regulating Vaccines

The current framework for testing and regulating vaccines was established before the realization that vaccines, in addition to their effect against the vaccine-specific disease, may also have "non-specific effects" affecting the risk of unrelated diseases. Accumulating evidence from epidemiological studies shows that vaccines in some situations can affect all-cause mortality and morbidity in ways that are not explained by the prevention of the vaccine-targeted disease. Live attenuated vaccines have sometimes been associated with decreases in mortality and morbidity that are greater than anticipated. In contrast, some non-live vaccines have in certain contexts been associated with increases in all-cause mortality and morbidity. The non-specific effects are often greater for female than male individuals. Immunological studies have provided several mechanisms that explain how vaccines might modulate the immune response to unrelated pathogens, such as through trained innate immunity, emergency granulopoiesis, and heterologous T-cell immunity. These insights suggest that the framework for the testing, approving, and regulating vaccines needs to be updated to accommodate non-specific effects. Currently, non-specific effects are not routinely captured in phase I-III clinical trials or in the post-licensure safety surveillance. For instance, an infection with Streptococcus pneumoniae occurring months after a diphtheria-tetanus-pertussis vaccination would not be considered an effect of the vaccination, although evidence indicates it might well be for female individuals. Here, as a starting point for discussion, we propose a new framework that considers the non-specific effects of vaccines in both phase III trials and post-licensure.

Can BCG vaccination at first health-facility contact reduce early infant mortality? Study protocol for a cluster-randomised trial (CS-BCG)

INTRODUCTION

Increasing evidence suggests that the BCG vaccine has non-specific effects, altering the susceptibility to non-tuberculous infections. Thus, early BCG vaccination may reduce mortality. BCG is recommended at birth but is often delayed. Vaccination opportunities are missed due to multidose vials not being opened for a few children. We will assess the effect of making BCG available at the first health-facility contact on early infant mortality and morbidity in a rural setting in Guinea-Bissau.

METHODS AND ANALYSIS

In a cluster-randomised crossover trial, we randomise 23 health centres to two different treatment groups. In half of the health centres, BCG is provided as per current practice; in the remaining health centres, we make BCG available everyday to allow opening a vial of BCG if there is just one eligible child present. The randomisation of centres will be crossed over after 12 months and enrolment will continue for another 12 months.We will use logistic regression models with adjustment for village to assess the effect of making BCG available at the first health-facility contact. The main outcome is non-accidental mortality between day 1 and day 42 after birth. We will adjust for sex, health centre, period (before/after crossover) and level of surveillance (level 1 or level 2). Further analyses include assessment of the effect on hospital admission and a cost-effectiveness evaluation.

ETHICS AND DISSEMINATION

If BCG vaccination reduces early infant mortality, missed opportunities and delays of vaccinations expose infants in several low-income countries to unnecessary excess mortality risk. The present trial will provide information on the effect of implementing a feasible intervention, where all children receive BCG at their first health-facility contact. Consent is obtained from all pregnant women registered as part of the trial. The results of the study will be published and communicated to the National Institute of Public Health in Guinea-Bissau.

TRIAL REGISTRATION NUMBER

NCT04658680; Clinicaltrials.gov.

The effect of BCG revaccination on all-cause mortality beyond infancy: 30-year follow-up of a population-based, double-blind, randomised placebo-controlled trial in Malawi

BACKGROUND

Trials of BCG vaccination to prevent or reduce severity of COVID-19 are taking place in adults, some of whom have been previously vaccinated, but evidence of the beneficial, non-specific effects of BCG come largely from data on mortality in infants and young children, and from in-vitro and animal studies, after a first BCG vaccination. We assess all-cause mortality following a large BCG revaccination trial in Malawi.

METHODS

The Karonga Prevention trial was a population-based, double-blind, randomised controlled in Karonga District, northern Malawi, that enrolled participants between January, 1986, and November, 1989. The trial compared BCG (Glaxo-strain) revaccination versus placebo to prevent tuberculosis and leprosy. 46 889 individuals aged 3 months to 75 years were randomly assigned to receive BCG revaccination (n=23 528) or placebo (n=23 361). Here we report mortality since vaccination as recorded during active follow-up in northern areas of the district in 1991-94, and in a demographic surveillance follow-up in the southern area in 2002-18. 7389 individuals who received BCG (n=3746) or placebo (n=3643) lived in the northern follow-up areas, and 5616 individuals who received BCG (n=2798) or placebo (n=2818) lived in the southern area. Year of death or leaving the area were recorded for those not found. We used survival analysis to estimate all-cause mortality.

FINDINGS

Follow-up information was available for 3709 (99·0%) BCG recipients and 3612 (99·1%) placebo recipients in the northern areas, and 2449 (87·5%) BCG recipients and 2413 (85·6%) placebo recipients in the southern area. There was no difference in mortality between the BCG and placebo groups in either area, overall or by age group or sex. In the northern area, there were 129 deaths per 19 694 person-years at risk in the BCG group (6·6 deaths per 1000 person-years at risk [95% CI 5·5-7·8]) versus 133 deaths per 19 111 person-years at risk in the placebo group (7·0 deaths per 1000 person-years at risk [95% CI 5·9-8·2]; HR 0·94 [95% CI 0·74-1·20]; p=0·62). In the southern area, there were 241 deaths per 38 399 person-years at risk in the BCG group (6·3 deaths per 1000 person-years at risk [95% CI 5·5-7·1]) versus 230 deaths per 38 676 person-years at risk in the placebo group (5·9 deaths per 1000 person-years at risk [95% CI 5·2-6·8]; HR 1·06 [95% CI 0·88-1·27]; p=0·54).

INTERPRETATION

We found little evidence of any beneficial effect of BCG revaccination on all-cause mortality. The high proportion of deaths attributable to non-infectious causes beyond infancy, and the long time interval since BCG for most deaths, might obscure any benefits.

FUNDING

British Leprosy Relief Association (LEPRA); Wellcome Trust.

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

Bacillus Calmette-Guérin (BCG) vaccine against tuberculosis (TB) is recommended at birth in TB-endemic areas. Currently, BCG vaccination programmes use "BCG vaccination coverage by 12 months of age" as the performance indicator. Previous studies suggest that BCG-vaccinated children, who develop a scar, have better overall survival compared with BCG-vaccinated children, who do not develop a scar. We summarized the available studies of BCG scarring and child survival. A structured literature search for studies with original data and analysis of BCG scarring and mortality were performed. Combined analyses on the effect of BCG scarring on overall mortality. We identified six studies covering seven cohorts, all from Guinea-Bissau, West Africa, with evaluation of BCG scarring amongst BCG-vaccinated children and follow-up for mortality. Determinants of BCG scarring were BCG strain, intradermal injection route, size of injection wheal, and co-administered vaccines and micronutrients. In a combined analysis, having a BCG scar vs. no BCG scar was associated with a mortality rate ratio (MRR) of 0.61 (95% CI: 0.51-0.74). The proportion with a BCG scar varied from 52 to 93%; the estimated effect of a BCG scar was not associated with the scar prevalence. The effect was strongest in the first (MRR = 0.48 (0.37-0.62)) and second (MRR = 0.63 (0.44-0.92)) year of life, and in children BCG-vaccinated in the neonatal period (MRR = 0.45 (0.36-0.55)). The effect was not explained by protection against TB. Confounding and genetic factors are unlikely to explain the strong association between BCG scarring and subsequent survival. Including "BCG scar prevalence" as a BCG vaccination programme performance indicator should be considered. The effect of revaccinating scar-negative children should be studied.

Can BCG be useful to mitigate the COVID-19 pandemic? A Canadian perspective

There is ample evidence from in vitro, animal and human studies that the Bacillus Calmette-Guerin (BCG) vaccine epigenetically reprograms innate immunity to provide “off target” protection against pathogens other than mycobacteria. This process has been termed “trained immunity”. Although recent ecological studies suggested an association between BCG policies and the frequency or severity of COVID-19 in different countries, the interpretation of these results is challenging. For this reason, a case-control study aiming to test this hypothesis has been initiated in Quebec. Several phase III clinical trials are underway, including one in Canada, to assess the efficacy of BCG against SARS-CoV-2 infection (results expected in 2021). In the past, BCG has been widely used in Canada but current indications are restricted to high-risk individuals and communities experiencing TB outbreaks as well as for the treatment of bladder cancer. The potential implication of BCG as an interim measure to mitigate COVID-19 is the subject of widespread discussion in the scientific community and can be considered for the vulnerable population in Canada. To conclude, BCG vaccination should be placed on the agenda of research funding agencies, scientific advisory committees on immunization and federal/provincial/territorial public health authorities.

Bacille Calmette Guérin (BCG) and new TB vaccines: Specific, cross-mycobacterial and off-target effects

The Bacille Calmette Guérin (BCG) vaccine was developed over a century ago and has become one of the most used vaccines without undergoing a modern vaccine development life cycle. Despite this, the vaccine has protected many millions from severe and disseminated forms of tuberculosis (TB). In addition, BCG has cross-mycobacterial effects against non-tuberculous mycobacteria and off-target (also called non-specific or heterologous) effects against other infections and diseases. More recently, BCG's effects on innate immunity suggest it might improve the immune response against viral respiratory infections including SARS-CoV-2. New TB vaccines, developed over the last 30 years, show promise, particularly in prevention of progression to disease from TB infection in young adults. The role of BCG in the context of new TB vaccines remains uncertain as most participants included in trials have been previously BCG immunised. BCG replacement vaccines are in efficacy trials and these may also have off-target effects.

Vaccinology: time to change the paradigm?

The existing vaccine paradigm assumes that vaccines only protect against the target infection, that effective vaccines reduce mortality corresponding to the target infection's share of total mortality, and that the effects of vaccines are similar for males and females. However, epidemiological vaccine research has generated observations that contradict these assumptions and suggest that vaccines have important non-specific effects on overall health in populations. These include the observations that several live vaccines reduce the incidence of all-cause mortality in vaccinated compared with unvaccinated populations far more than can be explained by protection against the target infections, and that several non-live vaccines are associated with increased all-cause mortality in females. In this Personal View we describe current observations and contradictions and define six emerging principles that might explain them. First, that live vaccines enhance resistance towards unrelated infections. Second, non-live vaccines enhance the susceptibility of girls to unrelated infections. Third, the most recently administered vaccination has the strongest non-specific effects. Fourth, combinations of live and non-live vaccines given together have variable non-specific health effects. Fifth, vaccinating children with live vaccines in the presence of maternal immunity enhances beneficial non-specific effects and reduces mortality. Finally, vaccines might interact with other co-administered health interventions, for example vitamin A supplementation. The potential implications for child health are substantial. For example, if BCG vaccination was given to children at birth, if higher measles vaccination coverage could be obtained, if diphtheria, tetanus, and pertussis-containing vaccines were not given with or after measles vaccine, or if the BCG strain with the best non-specific effects could be used consistently, then child mortality could be considerably lower. Pursuing these emerging principles could improve our understanding and use of vaccines globally.

Neonatal BCG vaccination and child survival in TB-exposed and TB-unexposed children: a prospective cohort study

OBJECTIVES

To assess the association between neonatal BCG vaccination and mortality between 28 days and 3 years of age among tuberculosis (TB)-exposed and TB-unexposed children.

DESIGN

Prospective cohort study.

SETTING

Bandim Health Project runs an urban Health and Demographic Surveillance site in Guinea-Bissau with registration of mortality, vaccination status and TB cases.

PARTICIPANTS

Children entered the analysis when their vaccination card was inspected after 28 days of age and remained under surveillance to 3 years of age. Children residing in the same house as a TB case were classified as TB-exposed from 3 months prior to case registration to the end of follow-up.

METHODS

Using Cox-proportional hazards models with age as underlying time scale, we compared mortality of children with and without neonatal BCG between October 2003 and September 2017.

MAIN OUTCOME MEASURE

HR for neonatal BCG compared with no neonatal BCG by TB-exposure status.

RESULTS

Among the 39 421 children who entered the analyses, 3022 (8%) had observation time as TB-exposed. In total, 84% of children received neonatal BCG. Children with neonatal BCG had lower mortality both in TB-exposed (adjusted HR: 0.57 (0.26 to 1.27)) and in TB-unexposed children (HR: 0.57 (95% CI 0.47 to 0.69)) than children without neonatal BCG. Children exposed to TB had higher mortality than TB-unexposed children if they had not received neonatal BCG.

CONCLUSION

Neonatal BCG vaccination was associated with lower mortality among both TB-exposed and TB-unexposed children, consistent with neonatal BCG vaccination having beneficial non-specific effects. Interventions to increase timely BCG vaccination are urgently warranted.

Licensed Bacille Calmette-Guérin (BCG) formulations differ markedly in bacterial viability, RNA content and innate immune activation

BACKGROUND

Bacille Calmette-Guérin (BCG), the live attenuated tuberculosis vaccine, is manufactured under different conditions across the globe generating formulations that may differ in clinical efficacy. Innate immune recognition of live BCG contributes to immunogenicity suggesting that differences in BCG viability may contribute to divergent activity of licensed formulations.

METHODS

We compared BCG-Denmark (DEN), -Japan (JPN), -India (IND), -Bulgaria (BUL) and -USA in vitro with respect to a) viability as measured by colony-forming units (CFU), mycobacterial membrane integrity, and RNA content, and b) cytokine/chemokine production in newborn cord and adult peripheral blood.

RESULTS

Upon culture, relative growth was BCG-USA > JPN ≫ DEN > BUL = IND. BCG-IND and -BUL demonstrated >1000-fold lower growth than BCG-JPN in 7H9 medium and >10-fold lower growth in commercial Middlebrook 7H11 medium. BCG-IND demonstrated significantly decreased membrane integrity, lower RNA content, and weaker IFN-γ inducing activity in whole blood compared to other BCGs. BCG-induced whole blood cytokines differed significantly by age, vaccine formulation and concentration. BCG-induced cytokine production correlated with CFU, suggesting that mycobacterial viability may contribute to BCG-induced immune responses.

CONCLUSIONS

Licensed BCG vaccines differ markedly in their content of viable mycobacteria possibly contributing to formulation-dependent activation of innate and adaptive immunity and distinct protective effects.

Insights and challenges in tuberculosis vaccine development

Tuberculosis kills more people than any other pathogen and the need for a universally effective vaccine has never been greater. An effective vaccine will be a key tool in achieving the targets set by WHO in the End TB Strategy. Tuberculosis vaccine development is difficult and slow. Substantial progress has been made in research and development of tuberculosis vaccines in the past 20 years, and two clinical trial results from 2018 provide reason for optimism. However, many challenges to the successful licensure and deployment of an effective tuberculosis vaccine remain. The development of new tools for vaccine evaluation might facilitate these processes, and continued collaborative working and sustained funding will be essential.

Developing the concept of beneficial non-specific effect of live vaccines with epidemiological studies

BACKGROUND

Epidemiological and immunological studies are increasingly reporting non-specific effects (NSEs) of vaccines; i.e. vaccines may affect the risk and severity of non-targeted infections. We reviewed how epidemiological studies developed the concept of beneficial NSEs of live vaccines.

SOURCES

This is a personal narrative of how we came to pursue the concept of NSEs in studies of measles vaccine (MV) from the late 1970s. We also searched Pubmed for epidemiological studies of nonspecific/non-specific effects (NSEs) of the most common human vaccines.

CONTENT

When smallpox vaccine was introduced around 1800, bacillus Calmette-Guérin (BCG) against tuberculosis in the 1920s and oral polio vaccine (OPV) in the 1960s, there were suggestions that these live attenuated vaccines reduced mortality more than expected. However, scientific follow-up was limited and the concept of beneficial NSEs did not become mainstream. We observed beneficial NSEs after MV was introduced in low-income countries in the 1970s. Subsequent observational studies and randomized trials confirmed beneficial NSEs of smallpox vaccine, BCG and OPV. Recently, beneficial NSEs have been claimed for the non-live diphtheria-tetanus-pertussis and rabies vaccines. However, no non-live vaccine has yet been documented to produce beneficial NSEs.

IMPLICATIONS

Observational and experimental research has shown beneficial NSEs of four live attenuated vaccines: smallpox vaccine, BCG, OPV and MV. With immunological evidence now supporting the epidemiological observations, it is urgent to take both the specific and NSEs into account in the planning of vaccination programmes.

The impact of vaccines on heterologous adaptive immunity

BACKGROUND

Vaccines induce antigen-specific memory in adaptive immune cells that enables long-lived protection against the target pathogen. In addition to this, several vaccines have beneficial effects greater than protection against their target pathogen. These non-specific effects are proposed to be the result of vaccine-induced immunomodulation. In the case of bacille Calmette-Guérin (BCG) vaccine, this involves induction of innate immune memory, termed 'trained immunity', in monocytes and natural killer cells.

OBJECTIVES

This review discusses current evidence for vaccine-induced immunomodulation of adaptive immune cells and heterologous adaptive immune responses.

CONTENT

The three vaccines that have been associated with changes in all-cause infant mortality: BCG, diphtheria-tetanus-pertussis (DTP) and measles-containing vaccines (MCV) alter T-cell and B-cell immunity. The majority of studies that investigated non-specific effects of these vaccines on the adaptive immune system report changes in numbers or proportions of adaptive immune cell populations. However, there is also evidence for effects of these vaccines on adaptive immune cell function and responses to heterologous stimuli. There is some evidence that, in addition to BCG, DTP and MCV, other vaccines (that have not been associated with changes in all-cause mortality) may alter adaptive immune responses to unrelated stimuli.

IMPLICATIONS

This review concludes that vaccines alter adaptive immune cell populations and heterologous immune responses. The non-specific effects differ between various vaccines and their effects on heterologous adaptive immune responses may also involve bystander activation, cross-reactivity and other as yet undefined mechanisms. This has major implications for future vaccine design and vaccination scheduling.