Perspectives on development and advancement of new tuberculosis vaccines.

Tuberculosis (TB) remains a leading cause of death worldwide and is estimated to have caused 1.3 million deaths worldwide in 2022. Approximately one quarter of the world's population are infected with Mycobacterium tuberculosis, of whom up to 10% will progress to developing active TB disease. Achieving the World Health Organization End TB Strategy targets of a 95% reduction in TB mortality and a 90% reduction in TB incidence worldwide by 2035 remains a daunting task. The continuing spread of multidrug-resistant TB adds another obstacle to achieving global TB control. Larger funding pledges coupled with technological advances have recently enabled the enhancement of TB vaccine development efforts. These are yielding a pipeline of over 17 products currently in different stages of clinical trials. Emerging promising phase I and II trial results and advancement to phase III trials have necessitated "vaccine preparedness" in parallel so that a smooth transition from any positive clinical trial result to phase IV evaluation and implementation into policy and practice can follow. Promotion of a human rights-based approach, which recognizes and upholds the fundamental rights of all affected by the disease, is essential to ensure universal access to quality TB vaccines, regardless of their background or personal circumstances.

Measles vaccination and reduced child mortality: Prevention of immune amnesia or beneficial non-specific effects of measles vaccine?

Measles vaccine (MV) has been observed to reduce all-cause mortality more than explained by prevention of measles infection. Recently, prevention of "measles-induced immune amnesia" (MIA) has been proposed as an explanation for this larger-than-anticipated beneficial effect of measles vaccine (MV). According to the "MIA hypothesis", immune amnesia leads to excess non-measles morbidity and mortality, that may last up to five years after measles infection, but may be prevented by MV. However, the benefits of MV-vaccinated children could also be due to beneficial non-specific effects (NSEs) of MV, reducing the risk of non-measles infections (The "NSE hypothesis"). The epidemiological studies do provide some support for MIA, as exposure to measles infection before 6 months of age causes long-term MIA, and over 6 months of age for 2-3 months. However, in children over 6 months of age, the MIA hypothesis is contradicted by several epidemiological patterns: First, in community studies that adjusted for MV status, children surviving acute measles infection had lower mortality than uninfected controls (44%(95%CI: 0-69%)). Second, in six randomised trials and six observational studies comparing MV-vaccinated and MV-unvaccinated children, the benefit of MV changed minimally from 54%(43-63%) to 49%(37-59%) when measles cases were censored in the survival analysis, making it unlikely that prevention of measles and its long-term consequences explained much of the reduced mortality. Third, several studies conducted in measles-free contexts still showed significantly lower mortality after MV (55%(40-67%)). Fourth, administration of MV in the presence of maternal measles antibody (MatAb) is associated with much stronger beneficial effect for child survival than administration of MV in the absence of MatAb (55%(35-68%) lower mortality). The MIA hypothesis alone cannot explain the strongly beneficial effects of MV on child survival. Conversely, the hypothesis that MV has beneficial non-specific immune training effects is compatible with all available data. Consideration should be given to continuing MV even when measles has been eradicated.

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.

Randomized clinical trials of COVID-19 vaccines: Do adenovirus-vector vaccines have beneficial non-specific effects?

We examined the possible non-specific effects of novel mRNA- and adenovirus-vector COVID-19 vaccines by reviewing the randomized control trials (RCTs) of mRNA and adenovirus-vector COVID-19 vaccines. We calculated mortality risk ratios (RRs) for mRNA COVID-19 vaccines vs. placebo recipients and compared them with the RR for adenovirus-vector COVID-19 vaccine recipients vs. controls. The RR for overall mortality of mRNA vaccines vs. placebo was 1.03 (95% confidence interval [CI]: 0.63-1.71). In the adenovirus-vector vaccine RCTs, the RR for overall mortality was 0.37 (0.19-0.70). The two vaccine types differed significantly with respect to impact on overall mortality (p = 0.015). The RCTs of COVID-19 vaccines were unblinded rapidly, and controls were vaccinated. The results may therefore not be representative of the long-term effects. However, the data argue for performing RCTs of mRNA and adenovirus-vector vaccines head-to-head comparing long-term effects on overall mortality.

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.

The impact of BCG dose and revaccination on trained immunity.

The innate immune system can display heterologous memory-like responses termed trained immunity after stimulation by certain vaccinations or infections. In this randomized, placebo-controlled trial, we investigated the modulation of Bacille Calmette-Guérin (BCG)-induced trained immunity by BCG revaccination or high-dose BCG administration, in comparison to a standard dose. We show that monocytes from all groups of BCG-vaccinated individuals exerted increased TNFα production after ex-vivo stimulation with various unrelated pathogens. Similarly, we observed increased amounts of T-cell-derived IFNγ after M. tuberculosis exposure, regardless of the BCG intervention. NK cell cytokine production, especially after heterologous stimulation with the fungal pathogen Candida albicans, was predominantly boosted after high dose BCG administration. Cytokine production capacity before vaccination was inversely correlated with trained immunity. While the induction of a trained immunity profile is largely dose- or frequency independent, baseline cytokine production capacity is associated with the magnitude of the innate immune memory response after BCG vaccination.

One vaccine to counter many diseases? Modeling the economics of oral polio vaccine against child mortality and COVID-19.

Introduction: Recent reviews summarize evidence that some vaccines have heterologous or non-specific effects (NSE), potentially offering protection against multiple pathogens. Numerous economic evaluations examine vaccines' pathogen-specific effects, but less than a handful focus on NSE. This paper addresses that gap by reporting economic evaluations of the NSE of oral polio vaccine (OPV) against under-five mortality and COVID-19. Materials and methods: We studied two settings: (1) reducing child mortality in a high-mortality setting (Guinea-Bissau) and (2) preventing COVID-19 in India. In the former, the intervention involves three annual campaigns in which children receive OPV incremental to routine immunization. In the latter, a susceptible-exposed-infectious-recovered model was developed to estimate the population benefits of two scenarios, in which OPV would be co-administered alongside COVID-19 vaccines. Incremental cost-effectiveness and benefit-cost ratios were modeled for ranges of intervention effectiveness estimates to supplement the headline numbers and account for heterogeneity and uncertainty. Results: For child mortality, headline cost-effectiveness was $650 per child death averted. For COVID-19, assuming OPV had 20% effectiveness, incremental cost per death averted was $23,000-65,000 if it were administered simultaneously with a COVID-19 vaccine <200 days into a wave of the epidemic. If the COVID-19 vaccine availability were delayed, the cost per averted death would decrease to $2600-6100. Estimated benefit-to-cost ratios vary but are consistently high. Discussion: Economic evaluation suggests the potential of OPV to efficiently reduce child mortality in high mortality environments. Likewise, within a broad range of assumed effect sizes, OPV (or another vaccine with NSE) could play an economically attractive role against COVID-19 in countries facing COVID-19 vaccine delays. Funding: The contribution by DTJ was supported through grants from Trond Mohn Foundation (BFS2019MT02) and Norad (RAF-18/0009) through the Bergen Center for Ethics and Priority Setting.

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.

Stopping Oral Polio Vaccine (OPV) After Defeating Poliomyelitis in Low- and Middle-Income Countries: Harmful Unintended Consequences? Review of the Nonspecific Effects of OPV.

Background: The live vaccines bacille Calmette-Guérin (BCG) and measles vaccine have beneficial nonspecific effects (NSEs) reducing mortality, more than can be explained by prevention of tuberculosis or measles infection. Live oral polio vaccine (OPV) will be stopped after polio eradication; we therefore reviewed the potential NSEs of OPV. Methods: OPV has been provided in 3 contexts: (1) coadministration of OPV and diphtheria-tetanus-pertussis (DTP) vaccine at 6, 10, and 14 weeks of age; (2) at birth (OPV0) with BCG; and (3) in OPV campaigns (C-OPVs) initiated to eradicate polio infection. We searched PubMed and Embase for studies of OPV with mortality as an outcome. We used meta-analysis to obtain the combined relative risk (RR) of mortality associated with different uses of OPV. Results: First, in natural experiments when DTP was missing, OPV-only compared with DTP + OPV was associated with 3-fold lower mortality in community studies (RR, 0.33 [95% confidence interval {CI}, .14-.75]) and a hospital study (RR, 0.29 [95% CI, .11-.77]). Conversely, when OPV was missing, DTP-only was associated with 3-fold higher mortality than DTP + OPV (RR, 3.23 [95% CI, 1.27-8.21]). Second, in a randomized controlled trial, BCG + OPV0 vs BCG + no OPV0 was associated with 32% (95% CI, 0-55%) lower infant mortality. Beneficial NSEs were stronger with early use of OPV0. Third, in 5 population-based studies from Guinea-Bissau and Bangladesh, the mortality rate was 24% (95% CI, 17%-31%) lower after C-OPVs than before C-OPVs. Conclusions: There have been few clinical polio cases reported in this century, and no confounding factors or bias would explain all these patterns. The only consistent interpretation is that OPV has beneficial NSEs, reducing nonpolio child mortality.

Effect of early two-dose measles vaccination on childhood mortality and modification by maternal measles antibody in Guinea-Bissau, West Africa: A single-centre open-label randomised controlled trial.

Background: Early 2-dose measles vaccine (MV) at 4 and 9 months of age vs. the WHO strategy of MV at 9 months of age reduced all-cause child mortality in a previous trial. We aimed to test two hypotheses: 1) a 2-dose strategy reduces child mortality between 4 and 60 months of age by 30%; 2) receiving early MV at 4 months in the presence versus absence of maternal measles antibodies (MatAb) reduces child mortality by 35%. Methods: Single-centre open-label community-based randomised controlled trial in Guinea-Bissau, with 2:1 block-randomisation by sex to a 2-dose (4 + 9 months) vs. 1-dose (9 months) MV strategy. Healthy children were eligible 4 weeks after the 3rd diphtheria-tetanus-pertussis-containing vaccine. Before randomisation a blood sample was collected to determine MatAb level. The primary outcome was all-cause mortality. Hazard ratios (HR) were derived from Cox regression in the per protocol population. We tested for interactions with national campaigns with oral polio vaccine (C-OPV). Trial registration: NCT01486355. Findings: Between August 2011-April 17th 2015, 6,636 children were enroled, 6,598[n2-dose=4,397; n1-dose=2,201] were included in the analysis of the primary outcome, The HR(2-dose/1-dose) between 4 and 60 months was 1.38 (95%CI: 0.92-2.06) [deaths: n2-dose=90; n1-dose=33]. Before the 9-month MV and the HR(1-dose/no dose) was 0.94 (0.45-1.96) [deaths: n2-dose=21; n1-dose=11]. The HR(2-dose/1-dose) was 0.81 (0.29-2.22) for children, who received no C-OPV [deaths/children: n2-dose=10/2,801; n1-dose=6/1,365], and 4.73 (1.44-15.6) for children, who received C-OPV before and after enrolment (p for interaction=0.027) [deaths/children: n2-dose=27/1,602; n1-dose=3/837]. In the 2-dose group receiving early MV at 4 months, mortality was 50% (20-68%) lower for those vaccinated in the presence of MatAb vs. the absence of MatAb [deaths/children: nMatAb=51/3,132; nnoMatAb=31/1,028]. Interpretation: The main result contrasts with previous findings but may, though based on a small number of events, be explained by frequent OPV campaigns that reduced the mortality rate, but apparently interacted negatively with early MV. The beneficial non-specific effects of MV in the presence of MatAb should be investigated further. Funding: ERC, Danish National Research Foundation, the Danish Council for Development Research, Ministry of Foreign Affairs, Novo Nordisk Foundation, European Union and the Lundbeck Foundation.

Bacille Calmette-Guérin vaccine reprograms human neonatal lipid metabolism in vivo and in vitro.

Vaccines have generally been developed with limited insight into their molecular impact. While systems vaccinology enables characterization of mechanisms of action, these tools have yet to be applied to infants, who are at high risk of infection and receive the most vaccines. Bacille Calmette-Guérin (BCG) protects infants against disseminated tuberculosis (TB) and TB-unrelated infections via incompletely understood mechanisms. We employ mass-spectrometry-based metabolomics of blood plasma to profile BCG-induced infant responses in Guinea-Bissau in vivo and the US in vitro. BCG-induced lysophosphatidylcholines (LPCs) correlate with both TLR-agonist- and purified protein derivative (PPD, mycobacterial antigen)-induced blood cytokine production in vitro, raising the possibility that LPCs contribute to BCG immunogenicity. Analysis of an independent newborn cohort from The Gambia demonstrates shared vaccine-induced metabolites, such as phospholipids and sphingolipids. BCG-induced changes to the plasma lipidome and LPCs may contribute to its immunogenicity and inform the development of early life vaccines.

The Effect of a Second Dose of Measles Vaccine at 18 Months of Age on Nonaccidental Deaths and Hospital Admissions in Guinea-Bissau: Interim Analysis of a Randomized Controlled Trial.

BACKGROUND: The world is set on the eradication of measles. Continuation of the measles vaccine (MV) after eradication could still reduce morbidity because the MV has so-called beneficial nonspecific effects. We evaluated the effect of a "booster" dose of the MV on overall severe morbidity. METHODS: We conducted a randomized controlled trial among children aged 17.5 to 48 months in Guinea-Bissau, where the MV is recommended only at 9 months of age. At the time of this interim analysis, 3164 children had been allocated 1:1 to a second dose of measles vaccine (MV2) at 18 months of age or to no vaccine. Severe morbidity (a composite outcome of nonaccidental deaths and hospital admissions) rate ratios (SMRRs) were calculated by Cox regression analysis censored for national oral polio vaccine (OPV) campaigns. RESULTS: There were no measles cases during the trial period. There were 43 nonaccidental deaths or hospital admissions during follow-up. Severe morbidity was 2.6 per 100 person-years in the MV2 group and 3.6 per 100 person-years among controls; hence, the estimated effect of MV2 on severe morbidity was 28% (SMRR, 0.72; 95% confidence interval [CI], .38-1.38). At 12 months of follow-up, the number needed to treat to prevent 1 severe morbidity event was 137 children. After OPV campaigns, the estimated effect of MV2 was reduced to 9% (SMRR, 0.91; 95% CI, .46-1.81). CONCLUSIONS: MV2 may reduce nonmeasles severe morbidity by 28% (-38% to 62%), although this did not achieve statistical significance in this study. If significant in higher powered studies, this has major implications for child health, even after measles eradication. CLINICAL TRIALS REGISTRATION: NCT02943681.

Old vaccines for new infections: Exploiting innate immunity to control COVID-19 and prevent future pandemics.

The COVID-19 pandemic triggered an unparalleled pursuit of vaccines to induce specific adaptive immunity, based on virus-neutralizing antibodies and T cell responses. Although several vaccines have been developed just a year after SARS-CoV-2 emerged in late 2019, global deployment will take months or even years. Meanwhile, the virus continues to take a severe toll on human life and exact substantial economic costs. Innate immunity is fundamental to mammalian host defense capacity to combat infections. Innate immune responses, triggered by a family of pattern recognition receptors, induce interferons and other cytokines and activate both myeloid and lymphoid immune cells to provide protection against a wide range of pathogens. Epidemiological and biological evidence suggests that the live-attenuated vaccines (LAV) targeting tuberculosis, measles, and polio induce protective innate immunity by a newly described form of immunological memory termed "trained immunity." An LAV designed to induce adaptive immunity targeting a particular pathogen may also induce innate immunity that mitigates other infectious diseases, including COVID-19, as well as future pandemic threats. Deployment of existing LAVs early in pandemics could complement the development of specific vaccines, bridging the protection gap until specific vaccines arrive. The broad protection induced by LAVs would not be compromised by potential antigenic drift (immune escape) that can render viruses resistant to specific vaccines. LAVs might offer an essential tool to "bend the pandemic curve," averting the exhaustion of public health resources and preventing needless deaths and may also have therapeutic benefits if used for postexposure prophylaxis of disease.

Reduced Mortality After Oral Polio Vaccination and Increased Mortality After Diphtheria-tetanus-pertussis Vaccination in Children in a Low-income Setting.

PURPOSE: The diphtheria-tetanus-pertussis vaccine (DTP) and oral polio vaccine (OPV) were introduced in children 3 of 5 months of age in 1981-1983 in Bandim, in the capital of Guinea-Bissau. Because DTP has been linked to deleterious nonspecific effects (NSEs) and OPV to beneficial NSEs, we followed up this cohort to 3 years of age and examined the effects of DTP with OPV on all-cause mortality and the interactions of DTP and OPV with the measles vaccine (MV). METHODS: DTP and OPV were offered at 3 monthly community weighing sessions. Vaccination groups were defined by the last vaccine received. We compared overall mortality for different groups in Cox proportional hazards regression models, reporting hazards ratios (HRs) with 95% CIs. FINDINGS: The study cohort included 1491 children born in Bandim from December 1980 to December 1983. From 3 to 35 months of age, with censoring for MV, children vaccinated with DTP and/or OPV had higher mortality than both unvaccinated children (HR = l.66; 95% CI, 1.03-2.69) and OPV-only vaccinated children (HR = 2.81; 95% CI, 1.02-7.69); DTP-only vaccinated children had higher mortality than OPV-only vaccinated children (HR = 3.38; 95% CI, 1.15--9.93). In the age group of 3-8 months, before MV is administered, DTP-only vaccination was associated with a higher mortality than DTP with OPV (HR = 3.38; 95% CI, 1.59-7.20). Between 9 and 35 months of age, when MV is given, DTP-vaccinated and MV-unvaccinated children had higher mortality (HR = 2.76; 95% CI, 1.36-5.59) than children who had received MV after DTP, and among children who received DTP with MV or after MV, DTP-only vaccination was associated with a higher mortality than DTP with OPV (HR = 6.25; 95% CI, 2.55-15.37). IMPLICATIONS: Because the 2 vaccines had differential effects and the healthiest children were vaccinated first, selection biases are unlikely to explain the estimated impact on child survival. OPV had beneficial NSEs, and administration of OPV with DTP may have reduced the negative effects of DTP.

BCG vaccination in humans inhibits systemic inflammation in a sex-dependent manner.

BACKGROUNDInduction of innate immune memory, also termed trained immunity, by the antituberculosis vaccine bacillus Calmette-Guérin (BCG) contributes to protection against heterologous infections. However, the overall impact of BCG vaccination on the inflammatory status of an individual is not known; while induction of trained immunity may suggest increased inflammation, BCG vaccination has been epidemiologically associated with a reduced incidence of inflammatory and allergic diseases.METHODSWe investigated the impact of BCG (BCG-Bulgaria, InterVax) vaccination on systemic inflammation in a cohort of 303 healthy volunteers, as well as the effect of the inflammatory status on the response to vaccination. A targeted proteome platform was used to measure circulating inflammatory proteins before and after BCG vaccination, while ex vivo Mycobacterium tuberculosis- and Staphylococcus aureus-induced cytokine responses in peripheral blood mononuclear cells were used to assess trained immunity.RESULTSWhile BCG vaccination enhanced cytokine responses to restimulation, it reduced systemic inflammation. This effect was validated in 3 smaller cohorts, and was much stronger in men than in women. In addition, baseline circulating inflammatory markers were associated with ex vivo cytokine responses (trained immunity) after BCG vaccination.CONCLUSIONThe capacity of BCG to enhance microbial responsiveness while dampening systemic inflammation should be further explored for potential therapeutic applications.FUNDINGNetherlands Organization for Scientific Research, European Research Council, and the Danish National Research Foundation.

Circadian rhythm influences induction of trained immunity by BCG vaccination.

BACKGROUNDThe antituberculosis vaccine bacillus Calmette-Guérin (BCG) reduces overall infant mortality. Induction of innate immune memory, also termed trained immunity, contributes toward protection against heterologous infections. Since immune cells display oscillations in numbers and function throughout the day, we investigated the effect of BCG administration time on the induction of trained immunity.METHODSEighteen volunteers were vaccinated with BCG at 6 pm and compared with 36 age- and sex-matched volunteers vaccinated between 8 am and 9 am. Peripheral blood mononuclear cells were stimulated with Staphylococcus aureus and Mycobacterium tuberculosis before, as well as 2 weeks and 3 months after, BCG vaccination. Cytokine production was measured to assess the induction of trained immunity and adaptive responses, respectively. Additionally, the influence of vaccination time on induction of trained immunity was studied in an independent cohort of 302 individuals vaccinated between 8 am and 12 pm with BCG.RESULTSCompared with evening vaccination, morning vaccination elicited both a stronger trained immunity and adaptive immune phenotype. In a large cohort of 302 volunteers, early morning vaccination resulted in a superior cytokine production capacity compared with later morning. A cellular, rather than soluble, substrate of the circadian effect of BCG vaccination was demonstrated by the enhanced capacity to induce trained immunity in vitro in morning- compared with evening-isolated monocytes.CONCLUSIONSBCG vaccination in the morning induces stronger trained immunity and adaptive responses compared with evening vaccination. Future studies should take vaccine administration time into account when studying specific and nonspecific effects of vaccines; early morning should be the preferred moment of BCG administration.FUNDINGThe Netherlands Organization for Scientific Research, the European Research Council, and the Danish National Research Foundation.