Mutual interference on the immune response to yellow fever vaccine and a combined vaccine against measles, mumps and rubella

Immunogenicity of yellow fever vaccine co-administered with 13-valent pneumococcal conjugate vaccine in rural Gambia: A cluster-randomised trial

INTRODUCTION

Because booster doses of pneumococcal conjugate vaccine (PCV) may be given at a similar time to yellow fever vaccine (YF), it is important to assess the immune response to YF when co-administered with PCV. This has been investigated during a reduced-dose PCV trial in The Gambia.

METHODS

In this phase 4, parallel-group, cluster-randomized trial, healthy infants aged 0-10 weeks were randomly allocated to receive either a two-dose schedule of PCV13 with a booster dose co-administered with YF vaccine at age 9 months (1 + 1 co-administration) or YF vaccine administered separately at age 10 months (1 + 1 separate) or the standard three early doses of PCV13 with YF vaccine at age 9 months (3 + 0 separate). Blood samples were collected 28-35 days post-vaccination and YF neutralizing antibody (NA) titres were measured. Proportions with seroprotective YF NA titres ≥ 1:8 were calculated with 95 % confidence intervals (CI). Non-inferiority was demonstrated if the lower limit of the CI for the difference in proportions between the co-administration and separate groups was greater than - 10 %.

RESULTS

Forty-eight, 66, and 98 participants enrolled in 3 + 0 separate, 1 + 1 co-administration, and 1 + 1 separate groups respectively had NA results. Per protocol analysis of the 3 + 0 separate, 1 + 1 co-administration, 1 + 1 separate, and the combined 1 + 1 separate and 3 + 0 separate groups found that 81 %, 85 %, 92 %, and 88 % of participants respectively had YF NA titres ≥1:8. Results were similar with analysis by intention-to-treat. The difference in proportions comparing 1 + 1 co-administration and 1 + 1 separate groups was -7 % (95 % CI, -18 % to 3 %). The difference between 1 + 1 co-administration and 3 + 0 separate groups was 4 % (95 % CI, -10 % to 15 %). There was no statistical difference in the YF seroresponse when the YF vaccine was co-administered with PCV or administered separately.

CONCLUSIONS

No evidence was found of the non-inferiority of the seroresponse to YF vaccine when co-administered with PCV13. The levels of YF NA attaining seroprotection (NT ≥1:8) were high in all groups. PCV13 co-administered with YF vaccine at 9 months does not affect seroresponse to YF vaccine. http://www.isrctn.org/ - ISRCTN72821613.

Risk factors associated with in-hospital mortality during yellow fever outbreak in Brazil

Objective

To characterize the clinical manifestations of yellow fever disease and identify risk factors for mortality.

Methods

A retrospective study was conducted in the referral center for infectious diseases (Hospital Eduardo de Menezes-HEM) in Belo Horizonte, Minas Gerais, Brazil. Analysis included data from 283 patients with confirmed YF infection older than 13 years old who presented to HEM between January 2017 and June 2018. In-hospital mortality (hypothesis formulated after data collection), demographic factors and clinical and laboratory assessments were used.

Results

Study patients were mainly men (87.6%), with a median age of 46.0 (IQR 36.5, 57.0). 131 (46.3%) patients were admitted to the ICU, and 62 (22.0%) used invasive mechanical ventilation for a median of 2 days (IQR 1, 3). The median (IQR) total length of stay (LOS) in the ICU was 6 days (IQR 4, 8). The in-hospital mortality rate was 24.0%. Age was significantly higher in fatal (median 49.5, IQR 41.0, 61.0]) than in non-fatal cases [46 (36, 55)] (p < 0.01). Male sex was associated with an increased risk of death (RR 4.66, 95% CI 1.19, 18.2; p < 0.01). Most common symptoms and signs on admission to HEM were fever (31.9%), myalgia (27.8%), jaundice (24.3%), headache (23.9%), abdominal pain (16.1%), vomiting (12.2%), weakness (10.4%), and arthralgias (10.0%). Initial viral load above the cutoff of 4.45 log10 copies/mL was significantly associated with death prior to discharge (OR 12.2; CI 2.83, 92.3). Five factors were significantly related to increased odds of death prior to discharge: log-transformed AST (OR 3.65; CI 2.02, 7.81; p < 0.001), log-transformed INR (OR 7.40; CI 1.31, 33.0; p = 0.010), log-transformed lactate (OR 4.57; CI 1.48, 17.1; p = 0.013), log-transformed WBC (OR 4.33; CI 1.19, 18.5; p = 0.034), and age (OR 1.06; CI 1.01, 1.12; p = 0.026).

Conclusions and relevance

AST, INR, lactate, WBC, and age are statistically associated with death prior to discharge in YF patients. These clinical markers should be applied to improve patient screening and management during future YF epidemics.

Booster Vaccination against Yellow Fever in Gambian children-(BoVY) -a Phase 3 clinical trial to establish safety and immunogenicity of repeated YF vaccination in healthy Gambian children of different ages

Background

Yellow fever (YF) is a mosquito-borne and recently re-emerging viral haemorrhagic fever endemic to sub-Saharan Africa and South America. A highly effective vaccine against YF is licensed and recommended as part of routine childhood immunisation as a single dose at 9 months. Recent observational data demonstrate waning immunity following single primary vaccination and suggest that children in endemic areas may require booster vaccination.

Methods

This open-label, non-randomised clinical vaccine trial (ClinicalTrials.gov, NCT05332197, registered on 31 March 2022, URL: https://clinicaltrials.gov/study/NCT05332197) will assess the safety and immunogenicity of a booster dose of the licensed 17D YF vaccine in Gambian children. The trial will recruit 750 children in three cohorts of different ages (250 each). All children were vaccinated with the 17D YF vaccine at 9-10 months of age as part of clinical trials run by the Medical Research Council (MRC) Unit The Gambia, and are thus well-characterised, including basic clinical, anthropometric, and post-primary immunogenicity data. The children will receive booster doses at 15 months, 4 years, or 8.5 years. Serum samples will be taken before and 28 days after the booster, with additional sampling for exploratory endpoints in subgroups. Adverse events are solicited for the first three days following vaccination and recorded throughout the study period. The primary objective of the trial is to describe the safety and immunogenicity of the booster in the different age cohorts. Secondary objectives are to characterise the rate of sero-reversion (change from seropositive to seronegative) over a period of 9 months to 8 years following single primary vaccination and to profile the immune response to the booster to explore underlying mechanisms for the longevity of vaccine-induced antibody.

Discussion

The results of this trial are likely to directly impact WHO recommendations on whether booster vaccination is required for children in endemic areas, and if so, the optimal timing of such a booster.

The effect of BCG revaccination on the response to unrelated vaccines in urban Ugandan adolescents (POPVAC C): an open-label, randomised controlled trial

BACKGROUND

Immune responses induced by several important vaccines differ between populations, with reduced responses in low-income and rural settings compared with high-income and urban settings. BCG immunisation boosts immune responses to some unrelated vaccines in high-income populations. We aimed to test the hypothesis that BCG revaccination can enhance responses to unrelated vaccines in Ugandan schoolchildren.

METHODS

We conducted an open-label, randomised controlled trial to compare the effects of BCG revaccination versus no BCG revaccination on the immunogenicity of subsequent unrelated vaccines among adolescents aged 13-17 years who are participants in an urban Ugandan birth cohort study, in which BCG vaccination was documented at birth. Participants were excluded if they had received any of the trial vaccines or related agents when aged 5 years or older. Computer-generated 1:1 randomisation was implemented in REDCap. Participants were excluded if they were concurrently enrolled in other trials; had a clinically significant history of immunodeficiency, or serious psychiatric conditions or moderate to severe acute illnesses; were taking immunosuppressive medications; had allergies to vaccine components, a predisposition towards developing keloid scarring; positive HIV tests or pregnancy tests; were female participants who were lactating; or if they planned to use investigational drugs, vaccines, blood products, or any combination thereof. Trial participants assigned to the BCG revaccination group received the live parenteral BCG-Russia vaccine (Serum Institute of India, Pune, India; 0·1 mL intradermally, right upper arm) at week 0. All participants received yellow fever vaccine (YF-17D; Sanofi Pasteur, Lyon, France; 0·5 mL intramuscularly, left upper arm), live oral typhoid vaccine (Ty21a; PaxVax, London, UK; one capsule per day taken for three alternate days), and quadrivalent virus-like particle human papillomavirus (HPV) vaccine (Merck, Rahway, NJ, USA; 0·5 mL intramuscularly, left upper arm) at week 4; and toxoid vaccines (tetanus-diphtheria; Serum Institute of India; 0·5 mL intramuscularly, left upper arm) and an HPV booster at week 28. An additional HPV vaccination at week 8 was provided to female participants older than 14 years who had not previously been vaccinated. The primary outcomes were yellow fever neutralising antibody titres at 4 weeks post-YF-17D vaccination, Salmonella enterica serovar Typhi (henceforth S Typhi) O-lipopolysaccharide (O:LPS)-specific IgG concentration at 4 weeks post-Ty21a vaccination, and HPV-16 and HPV-18 L1 protein-specific IgG concentration at 4 weeks post-HPV vaccination. Primary outcome assays were conducted at week 8, and at week 52 for tetanus-diphtheria. We conducted an intention-to-treat analysis comparing log-transformed outcomes between trial groups, with results back-transformed to geometric mean ratios (GMRs). The safety population comprised all randomly allocated participants. The trial was registered at the ISRCTN Registry (ISRCTN10482904) and is complete.

FINDINGS

Between Aug 31 and Oct 12, 2020, we screened 376 potential participants for eligibility. We enrolled and randomly allocated 300 participants to the two groups (151 [50%] to the BCG group and 149 [50%] to the no BCG group). 178 (59%) of 300 participants were male and 122 (41%) were female. 142 (91%) of 151 participants in the BCG group and 139 (93%) of 149 in the no BCG group completed follow-up. There was no effect of BCG revaccination, compared with no BCG revaccination, on the response observed for any vaccine. Yellow fever plaque reduction neutralising reference tests (PRNT50) titres (the reciprocal of the last plasma dilution that reduced by 50%) had a GMR of 0·95 (95% CI 0·75-1·19; p=0·62) and PRNT90 (reciprocal of the last plasma dilution that reduced by 90%) had a GMR of 0·94 (0·74-1·19; p=0·60); IgG to S Typhi O:LPS was 0·99 (0·80-1·23; p=0·94); IgG to HPV-16 was 0·97 (0·69-1·35; p=0·85) and to HPV-18 was 1·03 (0·76-1·40; p=0·83); and toxoid-specific IgG for tetanus was 1·13 (0·87-1·47; p=0·36) and was 1·00 (0·87-1·16; p=0·97) for diphtheria. There were no serious adverse events in either group.

INTERPRETATION

We found no evidence that BCG revaccination is an effective strategy to improve immunogenicity of other vaccines in this low-income, urban setting.

FUNDING

UK Medical Research Council.

TRANSLATION

For the Luganda translation of the abstract see Supplementary Materials section.

Adverse events following immunization (AEFI) with fractional one-fifth and one-half doses of yellow fever vaccine compared to full dose in children 9-23 months old in Uganda, 2019-2020 - Preliminary report

BACKGROUND

In 2016, the World Health Organization recommended that a fractional dose of yellow fever (YF) vaccine could be used in persons 2 years of age or older in response to an emergency that resulted in a global shortage of available YF vaccine. However, this recommendation did not extend to the youngest age group licensed for YF vaccine because there were no published data on the use or safety of fractional dose YF vaccination in children aged 9-23 months. We conducted a single-blind randomized controlled trial, comparing the immunogenicity and safety of fractional one-fifth and one-half doses of Bio-Manguinhos 17DD YF vaccine with full dose in children aged 9-23 months old in Uganda. In this paper, we present the interim analysis on safety.

METHODS

Children aged 9-23 months presenting for routine well-child services were recruited for inclusion at one of three study sites. We collected data during March 26, 2019-August 31, 2020, on all adverse events following immunization (AEFI) during active surveillance for 28 days post-vaccination using multiple collection tools including a diary card with an objective measurement of fever. An independent team from the Uganda national AEFI Committee investigated and classified serious AEFI (SAE) according to Brighton Collaboration Criteria.

RESULTS

Among 1053 enrolled children, 672 (64%) were reported to have a non-serious AEFI (NSAE) and 17 (2%) were reported to have a SAE. The most common AEFI were diarrhoea, fever, and rash, each reported by 355 (34%), 338 (33%), and 188 (18%) participants, respectively. Among 17 participants with SAE, eight were reported to have had seizures and five were hospitalised for seizures or other causes (respiratory symptoms, gastrointestinal illness, malaria). Four SAEs (deaths) occurred >28 days after vaccination. There were no reported cases of pre-specified or vaccine-related SAEs. We observed no significant difference in frequency or severity of adverse events among the study groups.

CONCLUSIONS

Using comprehensive active surveillance monitoring, we did not identify any unexpected safety concerns among children aged <2 years receiving YF vaccination, including with the fractional doses. Although we identified a high number of both serious and non-serious AEFI, none were determined to be causally related to YF vaccination. These results provide evidence for the safety of fractional dose YF vaccination among children aged 9-23 months.

Development of a hydrogen peroxide-inactivated vaccine that protects against viscerotropic yellow fever in a non-human primate model

Yellow fever virus (YFV) is endemic in >40 countries and causes viscerotropic disease with up to 20%-60% mortality. Successful live-attenuated yellow fever (YF) vaccines were developed in the mid-1930s, but their use is restricted or formally contraindicated in vulnerable populations including infants, the elderly, and people with compromised immune systems. In these studies, we describe the development of a next-generation hydrogen peroxide-inactivated YF vaccine and determine immune correlates of protection based on log neutralizing index (LNI) and neutralizing titer-50% (NT50) studies. In addition, we compare neutralizing antibody responses and protective efficacy of hydrogen peroxide-inactivated YF vaccine candidates to live-attenuated YFV-17D (YF-VAX) in a rhesus macaque model of viscerotropic YF. Our results indicate that an optimized, inactivated YF vaccine elicits protective antibody responses that prevent viral dissemination and lethal infection in rhesus macaques and may be a suitable alternative for vaccinating vulnerable populations who are not eligible to receive replicating live-attenuated YF vaccines.

Humoral immunogenicity of primary yellow fever vaccination in infants and children: a systematic review, meta-analysis and meta-regression

BACKGROUND

Vaccination plays a critical role in mitigating the burden associated with yellow fever (YF). However, there is a lack of comprehensive evidence on the humoral response to primary vaccination in the paediatric population, with several questions debated, including the response when the vaccine is administered at early ages, the effect of co-administration with other vaccines, the duration of immunity and the use of fractional doses, among others. This study summarizes the existing evidence regarding the humoral response to primary YF vaccination in infants and children.

METHODS

Studies on the humoral response to primary YF vaccination in children aged 12 years or younger were reviewed. The humoral vaccine response rate (VRR), i.e. the proportion of children who tested positive for vaccine-induced YF-specific neutralizing antibodies, was pooled through random-effects meta-analysis and categorized based on the time elapsed since vaccination. Subgroup, meta-regression and sensitivity analyses were performed.

RESULTS

A total of 33 articles met the inclusion criteria, with all but one conducted in countries where YF is endemic. A total of 14 028 infants and children entered this systematic review. Within three months following vaccination, the pooled VRR was 91.9% (95% CI 89.8-93.9). A lower VRR was observed with the 17DD vaccine at the meta-regression analysis. No significant differences in immunogenicity outcomes were observed based on age, administration route, co-administration with other vaccines, or fractional dosing. Results also indicate a decline in VRR over time.

CONCLUSIONS

Primary YF vaccination effectively provides humoral immunity in paediatric population. However, humoral response declines over time, and this decline is observable after the first 18 months following vaccination. A differential response according to the vaccine substrain was also observed. This research has valuable implications for stimulating further research on the primary YF vaccination in infants and children, as well as for informing future policies.

Characterization of "Off-Target" Immune Modulation Induced by Live Attenuated Yellow Fever Vaccine

BACKGROUND

Live attenuated vaccines alter immune functions and are associated with beneficial outcomes. We previously demonstrated that live attenuated yellow fever virus (YFV) vaccine (LA-YF-Vax) dampens T-cell receptor (TCR) signaling in vitro via an RNA-based mechanism. We examined study participants before and after LA-YF-Vax to assess TCR-mediated functions in vivo.

METHODS

Serum samples and peripheral blood mononuclear cells (PBMCs) were obtained before and after LA-YF-Vax (with or without additional vaccines) or quadrivalent influenza vaccine. TCR-mediated activation was determined by interleukin 2 release or phosphorylation of the lymphocyte-specific Src kinase. TCR-regulating phosphatase (protein tyrosine phosphatase receptor type E [PTPRE]) expression was also measured.

RESULTS

Compared with prevaccination findings, LA-YF-Vax recipient PBMCs demonstrated transient reduction in interleukin 2 release after TCR stimulation and PTPRE levels, unlike in control participants who received quadrivalent influenza vaccine. YFV was detected in 8 of 14 participants after LA-YF-Vax. After incubation of healthy donor PBMCs in serum-derived extracellular vesicles prepared from LA-YF-Vax recipients, TCR signaling and PTPRE levels were reduced after vaccination, even in participants without detectable YFV RNA.

CONCLUSIONS

LA-YF-Vax reduces TCR functions and PTPRE levels after vaccination. Extracellular vesicles from serum recapitulated this effect in healthy cells. This likely contributes to the reduced immunogenicity for heterologous vaccines after LA-YF-Vax administration. Identification of specific immune mechanisms related to vaccines should contribute to understanding of the "off-target," beneficial effects of live vaccines.

Factors associated with yellow fever vaccine failure: A systematic literature review

INTRODUCTION

Considering that vaccination with yellow fever vaccine (YFV) is the most important method to prevent and control yellow fever (YF), this study synthesized evidence on factors associated with YFV failure.

METHODS

A systematic review (SR) was performed in the PubMed, Cochrane CENTRAL, Embase, and LILACS databases up to November 2019. Observational and experimental analytical epidemiological studies that analyzed the failure of YFV were included. This review followed the guidelines of the Preferred Reporting Items for Systematic Reviews and meta-Analyses.

RESULTS

A total of 1,466 articles were identified after searching the databases of which 46 were included in the qualitative analysis after applying the elegibility criteria. Our findings indicated that YFV confers protective immunity in different age groups; when produced by different producers; when administered simultaneously with a range of other vaccines; when used as fractional doses and when used with prophylactic and immunosuppressive therapies. It failed to produce a protective response in some pregnant women, children under two years of age, children with Kwashiorkor and when long periods of time have passed after vaccination. For individuals with human immunodeficiency virus (HIV), the results were divergent.

CONCLUSIONS

The results of this SR revealed the factors associated with the failure of the YFV, and the results can support recommendations on vaccination policies, support the safety of health professionals who work directly with immunization in the implementation of the vaccination schedule, in addition to guiding future research and enhance the credibility of YFV in the prevention of a serious disease such as YF.

Immune response to co-administration of measles, mumps, and rubella (MMR), and yellow fever vaccines: a randomized non-inferiority trial among one-year-old children in Argentina

BACKGROUND

In yellow fever (YF) endemic areas, measles, mumps, and rubella (MMR), and YF vaccines are often co-administered in childhood vaccination schedules. Because these are live vaccines, we assessed potential immune interference that could result from co-administration.

METHODS

We conducted an open-label, randomized non-inferiority trial among healthy 1-year-olds in Misiones Province, Argentina. Children were randomized to one of three groups (1:1:1): Co-administration of MMR and YF vaccines (MMR1YF1), MMR followed by YF vaccine four weeks later (MMR1YF2), or YF followed by MMR vaccine four weeks later (YF1MMR2). Blood samples obtained pre-vaccination and 28 days post-vaccination were tested for immunoglobulin G antibodies against measles, mumps, and rubella, and for YF virus-specific neutralizing antibodies. Non-inferiority in seroconversion was assessed using a -5% non-inferiority margin. Antibody concentrations were compared with Kruskal-Wallis tests.

RESULTS

Of 851 randomized children, 738 were correctly vaccinated, had ≥ 1 follow-up sample, and were included in the intention-to-treat population. Non-inferior seroconversion was observed for all antigens (measles seroconversion: 97.9% in the MMR1YF1 group versus 96.3% in the MMR1YF2 group, a difference of 1.6% [90% CI -1.5, 4.7]; rubella: 97.9% MMR1YF1 versus 94.7% MMR1YF2, a difference of 3.3% [-0.1, 6.7]; mumps: 96.7% MMR1YF1 versus 97.9% MMR1YF2, a difference of -1.3% [-4.1, 1.5]; and YF: 96.3% MMR1YF1 versus 97.5% YF1MMR2, a difference of -1.2% [-4.2, 1.7]). Rubella antibody concentrations and YF titers were significantly lower following co-administration; measles and mumps concentrations were not impacted.

CONCLUSION

Effective seroconversion was achieved and was not impacted by the co-administration, although antibody levels for two antigens were lower. The impact of lower antibody levels needs to be weighed against missed opportunities for vaccination to determine optimal timing for MMR and YF vaccine administration.

TRIAL REGISTRATION

The study was retrospectively registered in ClinicalTrials.gov (NCT03368495) on 11/12/2017.

Immunogenicity and safety of concomitant and sequential administration of yellow fever YF-17D vaccine and tetravalent dengue vaccine candidate TAK-003: A phase 3 randomized, controlled study

BACKGROUND

Yellow fever (YF) vaccination is often mandatory for travelers to YF-endemic areas. The areas with risk of YF partially overlap with those of dengue, for which there is currently no recommended vaccine available for dengue-naïve individuals. This phase 3 study assessed the immunogenicity and safety of concomitant and sequential administration of YF (YF-17D) and tetravalent dengue (TAK-003) vaccines in healthy adults aged 18-60 years living in areas of the US non-endemic for either virus.

METHODS

Participants were randomized 1:1:1 to receive the following vaccinations at Months 0, 3, and 6, respectively: YF-17D+placebo, TAK-003, and TAK-003 (Group 1); TAK-003+placebo, TAK-003, and YF-17D (Group 2); or YF-17D+TAK-003, TAK-003, and placebo (Group 3). The primary objective was to demonstrate non-inferiority (upper bound of 95% confidence interval [UB95%CI] of difference <5%) of YF seroprotection rate one month following concomitant administration of YF-17D and TAK-003 (Group 3) compared with YF-17D plus placebo (Group 1). The secondary objectives included demonstration of non-inferiority of YF and dengue geometric mean titers (GMTs) (UB95%CI for GMT ratio <2.0), and safety.

RESULTS

900 adults were randomized. YF seroprotection rates one month post-YF-17D (Month 1) were 99.5% and 99.1% in Group 1 and 3, respectively, and non-inferiority was demonstrated (UB95%CI = 2.69% i.e. <5%). Non-inferiority was also demonstrated for GMTs against YF one month post-YF-17D, and against DENV-2, -3, and -4 (UB95%CI <2), but not DENV-1 (UB95%CI: 2.22), one month post-second TAK-003 vaccination. Adverse event rates following TAK-003 were consistent with previous results, and no important safety risks were identified.

CONCLUSIONS

In this study, YF-17D vaccine and TAK-003 were immunogenic and well tolerated when sequentially or concomitantly administered. The non-inferiority of immune responses to YF-17D and TAK-003 was demonstrated for concomitant administration of the 2 vaccines compared to separate vaccination, except against DENV-1 but with GMTs similar to those observed in other TAK-003 trials.

TRIAL REGISTRATION

ClinicalTrials.gov identified: NCT03342898.

Safety and immunogenicity following co-administration of Yellow fever vaccine with Tick-borne encephalitis or Japanese encephalitis vaccines: Results from an open label, non-randomized clinical trial

BACKGROUND

Flavivirus infections pose a significant global health burden underscoring the need for the development of safe and effective vaccination strategies. Available flavivirus vaccines are from time to time concomitantly delivered to individuals. Co-administration of different vaccines saves time and visits to health care units and vaccine clinics. It serves to provide protection against multiple pathogens in a shorter time-span; e.g., for individuals travelling to different endemic areas. However, safety and immunogenicity-related responses have not been appropriately evaluated upon concomitant delivery of these vaccines. Therefore, we performed an open label, non-randomized clinical trial studying the safety and immunogenicity following concomitant delivery of the yellow fever virus (YFV) vaccine with tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JE) virus vaccines.

METHODS AND FINDINGS

Following screening, healthy study participants were enrolled into different cohorts receiving either TBEV and YFV vaccines, JEV and YFV vaccines, or in control groups receiving only the TBEV, JEV, or YFV vaccine. Concomitant delivery was given in the same or different upper arms for comparison in the co-vaccination cohorts. Adverse effects were recorded throughout the study period and blood samples were taken before and at multiple time-points following vaccination to evaluate immunological responses to the vaccines. Adverse events were predominantly mild in the study groups. Four serious adverse events (SAE) were reported, none of them deemed related to vaccination. The development of neutralizing antibodies (nAbs) against TBEV, JEV, or YFV was not affected by the concomitant vaccination strategy. Concomitant vaccination in the same or different upper arms did not significantly affect safety or immunogenicity-related outcomes. Exploratory studies on immunological effects were additionally performed and included studies of lymphocyte activation, correlates associated with germinal center activation, and plasmablast expansion.

CONCLUSIONS

Inactivated TBEV or JEV vaccines can be co-administered with the live attenuated YFV vaccine without an increased risk of adverse events and without reduced development of nAbs to the respective viruses. The vaccines can be delivered in the same upper arm without negative outcome. In a broader perspective, the results add valuable information for simultaneous administration of live and inactivated flavivirus vaccines in general.

TRIAL REGISTRATION

Eudra CT 2017-002137-32.

Seroconversion and antibody persistence after yellow fever vaccination in people living with HIV: impact of baseline HIV viral load and yellow fever seropositivity

BACKGROUND

Data on seroconversion rates following yellow fever (YF) vaccine and effect of revaccination in people living with HIV (PLWH) are scarce. We aimed at determining key factors for seroconversion after YF vaccine in PLWH and the role of preexisting neutralizing antibodies (NAbs) at vaccination.

METHODS

A retrospective cross-sectional study at several timepoints in two Belgian AIDS Reference Center. For each individual, plasma samples from three timepoints were selected: Timepoint 0 (TP0) in the year before administration of the YF vaccine, Timepoint 1 (TP1) in the year following the YF vaccine, Timepoint 2 (TP2) >1 year after the YF vaccine. Plasma samples were analysed for YF NAbs by plaque reduction neutralization test. The primary endpoint was the number of patients with protective levels of NAbs ≥ 1/10. A boosted immune response was defined as a 4-fold increase in serologic titres following revaccination.

RESULTS

Of the 160 PLWH included, protective levels of NAbs were present in 36%, 87% and 72% of subjects at baseline, at a median of 12 months and a median of 96 months after YF vaccination, respectively. Among vaccine recipients negative for YF NAbs at baseline (n = 102), 83% seroconverted. PLWH with undetectable HIV viral load (VL) at baseline were more likely to seroconvert (P < 0·01). A booster response was observed in only 17% of subjects with baseline seropositivity (n = 10 out of 58). In multivariate analysis, undetectable HIV VL at vaccination and baseline YF seropositivity were associated with persistent levels of protective NAbs at a median of 8 years after YF vaccination.

CONCLUSION

Undetectable HIV VL at baseline is associated with high rates of seroconversion. YF seropositivity before revaccination is associated with low rates of booster effect but a higher chance of long term persistent NAbs response, suggesting a benefit of revaccination in PLWH.

The early-life gut microbiome and vaccine efficacy

Vaccines are one of the greatest successes of public health, preventing millions of cases of disease and death in children each year. However, the efficacy of many vaccines can vary greatly between infants from geographically and socioeconomically distinct locations. Differences in the composition of the intestinal microbiome have emerged as one of the main factors that can account for variations in immunisation outcomes. In this Review, we assess the influence of the gut microbiota upon early life immunity, focusing on two important members of the microbiota with health-promoting and immunomodulatory properties: Bifidobacterium and Bacteroides. Additionally, we discuss their immune stimulatory microbial properties, interactions with the host, and their effect on vaccine responses and efficacy in infants. We also provide an overview of current microbiota-based approaches to enhance vaccine outcomes, and describe novel microbe-derived components that could lead to safer, more effective vaccines and vaccine adjuvants.

A High-Throughput Yellow Fever Neutralization Assay

Quick and accurate detection of neutralizing antibodies (nAbs) against yellow fever is essential in serodiagnosis during outbreaks for surveillance and to evaluate vaccine efficacy in population-wide studies. All of this requires serological assays that can process a large number of samples in a highly standardized format. Albeit being laborious, time-consuming, and limited in throughput, the classical plaque reduction neutralization test (PRNT) is still considered the gold standard for the detection and quantification of nAbs due to its sensitivity and specificity. Here, we report the development of an alternative fluorescence-based serological assay (SNTFLUO) with an equally high sensitivity and specificity that is fit for high-throughput testing with the potential for automation. Finally, our novel SNTFLUO was cross-validated in several reference laboratories and against international WHO standards, showing its potential to be implemented in clinical use. SNTFLUO assays with similar performance are available for the Japanese encephalitis, Zika, and dengue viruses amenable to differential diagnostics. IMPORTANCE Fast and accurate detection of neutralizing antibodies (nAbs) against yellow fever virus (YFV) is key in yellow fever serodiagnosis, outbreak surveillance, and monitoring of vaccine efficacy. Although classical PRNT remains the gold standard for measuring YFV nAbs, this methodology suffers from inherent limitations such as low throughput and overall high labor intensity. We present a novel fluorescence-based serum neutralization test (SNTFLUO) with equally high sensitivity and specificity that is fit for processing a large number of samples in a highly standardized manner and has the potential to be implemented for clinical use. In addition, we present SNTFLUO assays with similar performance for Japanese encephalitis, Zika, and dengue viruses, opening new avenues for differential diagnostics.

Catch-up immunization for adolescents and young adults during pre-travel consultation in Japan

Rubella and measles outbreaks in adults occur because of unimmunized or partially immunized status. Travel clinics play an important role in catch-up measles, rubella, mumps, and varicella immunization for adults. We evaluated the need for catch-up measles, rubella, mumps, and varicella immunization by young adults at our travel clinic. This retrospective observational study was conducted at the National Center for Global Health and Medicine from June 1, 2017 to May 31, 2018. Adults aged 16-49 years who received pre-travel consultation and had childhood immunization records were included. Individuals who fully or partially received planned measles, rubella, mumps, and varicella catch-up immunization were classified as "immunized." We calculated the proportion of "immunized" individuals and analyzed the factors associated with catch-up measles, rubella, mumps, and varicella immunization at pre-travel consultation using logistic regression analysis. Overall, 3,456 individuals received pre-travel consultations during the study period; 827 (336 men, median age 22 years) had childhood immunization records. The most common trip purposes were study (33%) and tourism (24%). The most common destination was Asia (39%). Catch-up immunization of any measles, rubella, mumps, and varicella vaccine was needed by 755 individuals. After consultation, 20-46% of these participants who needed catchup immunization received at least one dose of immunization. Factors that are negatively associated with measles, rubella, mumps, and varicella catch-up immunization were tourism (odds ratio 0.37 to 0.58), yellow fever vaccination (0.45 to 0.50) (excluding varicella), and each disease history (0.13 to 0.40) (excluding rubella and varicella). Further studies are needed to identify barriers to catch-up immunization.

Immunogenicity, duration of protection, effectiveness and safety of rubella containing vaccines: A systematic literature review and meta-analysis

BACKGROUND

Rubella containing vaccines (RCV) prevent rubella virus infection and subsequent congenital rubella syndrome (CRS). To update the evidence on immunogenicity, duration of protection, effectiveness and safety of RCV, we conducted a systematic literature review.

METHODS

We searched EMBASE and SCOPUS, using keywords for rubella vaccine in combination with immunogenicity (seroconversion and seropositivity), duration of protection, efficacy/effectiveness, and safety. Original research papers involving at least one dose of RCV (at any age), published between 1-1-2010 and 17-5-2019 were included. Where appropriate, meta-analyses were performed. Quality of included studies was assessed using GRADE methodology.

RESULTS

We included 36 papers (32 randomized controlled trials (RCTs) and 4 observational studies) on immunogenicity (RA27/3 strain) in children and adolescent girls, 14 papers (5 RCTs and 9 observational studies) on duration of protection, one paper on vaccine effectiveness (VE) (BRDII strain), and 74 studies on safety, including three on safety in pregnancy. Meta-analysis of immunogenicity data showed 99% seroconversion (95% CI: 98-99%) after a single dose of RCV in children, independent of co-administration with other vaccines. Seroconversion after RCV1 below 9 months of age (BRDII strain, at 8 months) was 93% (95% CI: 92-95%). For duration of protection, the included studies showed a seropositivity of 88%-100% measured 1-20 years after one or two RCV doses. The single study on VE of BRDII strain, reported 100% VE after one and two doses. Among 34,332 individuals participating in the RCTs, 140 severe adverse events (SAEs) were reported as possibly related to RCV. Among the case reports on SAEs, the association with RCV was confirmed in one report (on fulminant encephalitis). Among 3,000 pregnant women who were inadvertently vaccinated, no SAEs were reported.

CONCLUSIONS

One and two doses of RCV are highly immunogenic for a long period of time, effective in preventing rubella and CRS, and safe.

Vaccine failures: assessing yellow fever, measles, varicella, and mumps vaccines

Vaccination is one of the greatest public health interventions, based on its safety and effectiveness, but vaccination does not always mean immunization. Numerous aspects related both to the individual that receives the vaccine and the specificity of each vaccine administered are part of the process of obtaining adequate immunization, and it is essential to observe the aspects in order to avoid vaccine failures. The analysis of immunogenicity and effectiveness studies for the measles, varicella, and mumps vaccines point to the need to incorporate two doses into the basic vaccination calendars in order to control these diseases. Epidemiological studies that analyzed outbreaks of these diseases identified cases in individuals that received two doses of the vaccine, which may indicate likely secondary failure. For the yellow fever vaccine, the current discussion lies in the ideal number of doses for individual protection. The World Health Organization recommends a single dose for life. Despite the few reports in the literature concerning vaccine failures, immunogenicity studies demonstrate waning protection over the years, mainly in the pediatric age bracket. In the current scenario of elimination and control of diseases, associated with the decrease in the circulation of the wild-type viruses, the role of epidemiological surveillance is crucial for expanding knowledge on the multiple factors involved, culminating in vaccine failures and the emergence of outbreaks. Outbreaks of vaccine-preventable diseases negatively impact the credibility of immunization programs, leading to low vaccination coverage rates and interfering in vaccination's success.

Serological Protection 5-6 Years Post Vaccination Against Yellow Fever in African Infants Vaccinated in Routine Programmes

Introduction: Although effective live attenuated yellow fever (YF) vaccines have been available for over 9 decades sporadic outbreaks continue to occur in endemic regions. These may be linked to several factors including epidemiological factors such as vector and intermediate host distribution or vaccine coverage and efficacy. The World Health Organization's research priorities include gathering systematic evidence around the potential need for booster vaccination with YF vaccine whether this follows full or fractional doses in children. Knowledge on the longevity of response to YF vaccine and the implications of this response needs to be consolidated to guide future vaccination policy. Methods: We measured anti-YF IgG by microneutralization assay in a group of 481 African infants who had received YF vaccine as part of routine EPI programmes, to explore serological protection from YF 5-6 years post YF vaccination, as well as the effect of co variates. Findings: Notably, 22.2% of the cohort had undetectable antibody concentrations, with another 7.5% revealing concentrations below the threshold of seropositivity of 0.5 IU/mL. Sex, season, country and time since vaccination did not affect the longevity of antibody concentration or having antibody concentrations above a defined threshold. Conclusion: Roughly 30% of children in this cohort did not demonstrate anti-yellow fever antibody concentrations above the defined threshold of protection, with 20% having no demonstrable antibody. Knowledge on the longevity of response to YF vaccine and the implications needs to be consolidated to guide future vaccination policy.

To err is human: Clinical incident calls to a national travel health advice line

The National Travel Health Network and Centre (NaTHNaC) offers a telephone advice line for travel health practitioners in the UK. In this study we review clinical incidents concerning vaccines or malaria prophylaxis reported between 2016 and 2018. Two-hundred-and-fifty-one clinical incident calls were recorded, and commonly concerned scheduling or dosing errors. Vaccine scheduling errors accounted for 103 calls (41%), predominantly due to hepatitis A or hepatitis B vaccination either alone or in combination (65/103, 63%). Administration of yellow fever vaccine within 28 days of measles, mumps and rubella accounted for a further 15 (15%) calls. Twenty-six (10%) calls reported administration of a vaccine that was not recommended either for the destination or contraindicated in the traveller. Yellow fever was the commonest single vaccine discussed in 28.4% of vaccine clinical incidents reported. By highlighting common mistakes, we hope to raise awareness of common issues and improve practice in travel health.

Long-term immunity against yellow fever in children vaccinated during infancy: a longitudinal cohort study

BACKGROUND

A single dose of vaccine against yellow fever is routinely administered to infants aged 9-12 months under the Expanded Programme on Immunization, but the long-term outcome of vaccination in this age group is unknown. We aimed to evaluate the long-term persistence of neutralising antibodies to yellow fever virus following routine vaccination in infancy.

METHODS

We did a longitudinal cohort study, using a microneutralisation assay to measure protective antibodies against yellow fever in Malian and Ghanaian children vaccinated around age 9 months and followed up for 4·5 years (Mali), or 2·3 and 6·0 years (Ghana). Healthy children with available day-0 sera, a complete follow-up history, and no record of yellow fever revaccination were included; children seropositive for yellow fever at baseline were excluded. We standardised antibody concentrations with reference to the yellow fever WHO International Standard.

FINDINGS

We included 587 Malian and 436 Ghanaian children vaccinated between June 5, 2009, and Dec 26, 2012. In the Malian group, 296 (50·4%, 95% CI 46·4-54·5) were seropositive (antibody concentration ≥0·5 IU/mL) 4·5 years after vaccination. Among the Ghanaian children, 121 (27·8%, 23·5-32·0) were seropositive after 2·3 years. These results show a large decrease from the proportions of seropositive infants 28 days after vaccination, 96·7% in Mali and 72·7% in Ghana, reported by a previous study of both study populations. The number of seropositive children increased to 188 (43·1%, 95% CI 38·5-47·8) in the Ghanaian group 6·0 years after vaccination, but this result might be confounded by unrecorded revaccination or natural infection with wild yellow fever virus during a 2011-12 outbreak in northern Ghana.

INTERPRETATION

Rapid waning of immunity during the early years after vaccination of 9-month-old infants argues for a revision of the single-dose recommendation for this target population in endemic countries. The short duration of immunity in many vaccinees suggests that booster vaccination is necessary to meet the 80% population immunity threshold for prevention of yellow fever outbreaks.

FUNDING

Wellcome Trust.

Short-Lived Immunity After 17DD Yellow Fever Single Dose Indicates That Booster Vaccination May Be Required to Guarantee Protective Immunity in Children

The Yellow Fever (YF) vaccination is recommended for people living in endemic areas and represents the most effective strategy to reduce the risk of infection. Previous studies have warned that booster regimens should be considered to guarantee the long-term persistence of 17DD-YF-specific memory components in adults living in areas with YF-virus circulation. Considering the lower seroconversion rates observed in children (9-12 months of age) as compared to adults, this study was designed in order to access the duration of immunity in single-dose vaccinated children in a 10-years cross-sectional time-span. The levels of neutralizing antibodies (PRNT) and the phenotypic/functional memory status of T and B-cells were measured at a baseline, 30-45 days, 1, 2, 4, 7, and 10 years following primary vaccination. The results revealed that a single dose induced 85% of seropositivity at 30-45 days and a progressive time-dependent decrease was observed as early as 2 years and declines toward critical values (below 60%) at time-spans of ≥4-years. Moreover, short-lived YF-specific cellular immunity, mediated by memory T and B-cells was also observed after 4-years. Predicted probability and resultant memory analysis emphasize that correlates of protection (PRNT; effector memory CD8+ T-cells; non-classical memory B-cells) wane to critical values within ≥4-years after primary vaccination. Together, these results clearly demonstrate the decline of 17DD-YF-specific memory response along time in children primarily vaccinated at 9-12 months of age and support the need of booster regimen to guarantee the long-term persistence of memory components for children living in areas with high risk of YF transmission.

Evaluation of a Booster Dose of Pentavalent Rotavirus Vaccine Coadministered With Measles, Yellow Fever, and Meningitis A Vaccines in 9-Month-Old Malian Infants

Background

Rotavirus vaccines given to infants are safe and efficacious. A booster dose of rotavirus vaccine could extend protection into the second year of life in low-resource countries.

Methods

We conducted an open-label, individual-randomized trial in Bamako, Mali. We assigned 600 infants aged 9–11 months to receive measles vaccine (MV), yellow fever vaccine (YFV), and meningococcal A conjugate vaccine (MenAV) with or without pentavalent rotavirus vaccine (PRV). We assessed the noninferiority (defined as a difference of ≤10%) of seroconversion and seroresponse rates to MV, YFV, and MenAV. We compared the seroresponse to PRV.

Results

Seroconversion to MV occurred in 255 of 261 PRV recipients (97.7%) and 246 of 252 control infants (97.6%; difference, 0.1% [95% confidence interval {CI}, −4.0%–4.2%]). Seroresponse to YFV occurred in 48.1% of PRV recipients (141 of 293), compared with 52.2% of controls (153 of 293; difference, −4.1% [95% CI, −12.2%–4.0%]). A 4-fold rise in meningococcus A bactericidal titer was observed in 273 of 292 PRV recipients (93.5%) and 276 of 293 controls (94.2%; difference, −0.7% [95% CI, −5.2%–3.8%]). Rises in geometric mean concentrations of immunoglobulin A and immunoglobulin G antibodies to rotavirus were higher among PRV recipients (118 [95% CI, 91–154] and 364 [95% CI, 294–450], respectively), compared with controls (68 [95% CI, 50–92] and 153 [95% CI, 114–207], respectively).

Conclusions

PRV did not interfere with MV and MenAV; this study could not rule out interference with YFV. PRV increased serum rotavirus antibody levels.

Clinical Trials Registration

NCT02286895.

Antibody responses to yellow fever vaccine in 9 to 11-month-old Malian and Ghanaian children

Background: The World Health Organization recommends use of a single yellow fever (YF) vaccine dose for life and fractional doses in outbreaks when there are limited vaccine stocks. In endemic regions, this vaccine is given as part of routine infant immunization programs around 9 months of age. There is a need to better understand immune responses when vaccinating infants particularly in contexts where the child may be malnourished. Methods: Data from 393 Malian and Ghanaian infants who concomitantly received measles and YF vaccines at 9 to 11 months of age were retrospectively analyzed. Response to YF vaccine was examined for association with nutritional status at time of vaccination, sex, age, pre-vaccination titers and season of vaccination. Results: Neutralizing antibodies following vaccination were unaffected by season of vaccination, sex, pre-vaccination titers or nutritional status, though there was a trend to higher titers in males and children with higher height for age z-scores. Seroconversion rates differed significantly between countries (63.5 in Ghana vs. 91.0% in Mali). Conclusion: Longitudinal, prospective studies are needed to optimize the use of YF vaccine in infants in endemic settings. There may be a need for booster vaccinations and to compare various vaccine preparations to optimize the use of available vaccines.

Inherited IFNAR1 deficiency in otherwise healthy patients with adverse reaction to measles and yellow fever live vaccines

We describe two unrelated patients with inherited IFNAR1 deficiency who suffered from life-threatening infections following measles or yellow fever virus vaccination and were otherwise healthy.

Vaccination against measles, mumps, and rubella (MMR) and yellow fever (YF) with live attenuated viruses can rarely cause life-threatening disease. Severe illness by MMR vaccines can be caused by inborn errors of type I and/or III interferon (IFN) immunity (mutations in IFNAR2, STAT1, or STAT2). Adverse reactions to the YF vaccine have remained unexplained. We report two otherwise healthy patients, a 9-yr-old boy in Iran with severe measles vaccine disease at 1 yr and a 14-yr-old girl in Brazil with viscerotropic disease caused by the YF vaccine at 12 yr. The Iranian patient is homozygous and the Brazilian patient compound heterozygous for loss-of-function IFNAR1 variations. Patient-derived fibroblasts are susceptible to viruses, including the YF and measles virus vaccine strains, in the absence or presence of exogenous type I IFN. The patients’ fibroblast phenotypes are rescued with WT IFNAR1. Autosomal recessive, complete IFNAR1 deficiency can result in life-threatening complications of vaccination with live attenuated measles and YF viruses in previously healthy individuals.

Outflanking immunodominance to target subdominant broadly neutralizing epitopes

A major obstacle to vaccination against antigenically variable viruses is skewing of antibody responses to variable immunodominant epitopes. For influenza virus hemagglutinin (HA), the immunodominance of the variable head impairs responses to the highly conserved stem. Here, we show that head immunodominance depends on the physical attachment of head to stem. Stem immunogenicity is enhanced by immunizing with stem-only constructs or by increasing local HA concentration in the draining lymph node. Surprisingly, coimmunization of full-length HA and stem alters stem-antibody class switching. Our findings delineate strategies for overcoming immunodominance, with important implications for human vaccination.

Role of Multivalency and Antigenic Threshold in Generating Protective Antibody Responses

Vaccines play a vital role in protecting our communities against infectious disease. Unfortunately, some vaccines provide only partial protection or in some cases vaccine-mediated immunity may wane rapidly, resulting in either increased susceptibility to that disease or a requirement for more booster vaccinations in order to maintain immunity above a protective level. The durability of antibody responses after infection or vaccination appears to be intrinsically determined by the structural biology of the antigen, with multivalent protein antigens often providing more long-lived immunity than monovalent antigens. This forms the basis for the Imprinted Lifespan model describing the differential survival of long-lived plasma cell populations. There are, however, exceptions to this rule with examples of highly attenuated live virus vaccines that are rapidly cleared and elicit only short-lived immunity despite the expression of multivalent surface epitopes. These exceptions have led to the concept that multivalency alone may not reliably determine the duration of protective humoral immune responses unless a minimum number of long-lived plasma cells are generated by reaching an appropriate antigenic threshold of B cell stimulation. Examples of long-term and in some cases, potentially lifelong antibody responses following immunization against human papilloma virus (HPV), Japanese encephalitis virus (JEV), Hepatitis B virus (HBV), and Hepatitis A virus (HAV) provide several lessons in understanding durable serological memory in human subjects. Moreover, studies involving influenza vaccination provide the unique opportunity to compare the durability of hemagglutinin (HA)-specific antibody titers mounted in response to antigenically repetitive whole virus (i.e., multivalent HA), or detergent-disrupted “split” virus, in comparison to the long-term immune responses induced by natural influenza infection. Here, we discuss the underlying mechanisms that may be associated with the induction of protective immunity by long-lived plasma cells and their importance in future vaccine design.

The immunomodulatory effects of measles-mumps-rubella vaccination on persistence of heterologous vaccine responses

It is proposed that measles-containing vaccines have immunomodulatory effects which include a reduction in all-cause childhood mortality. The antibody response to heterologous vaccines provides a means to explore these immunomodulatory effects. This is the first study to investigate the influence of measles-mumps-rubella (MMR) vaccine on the persistence of antibodies to a broad range of heterologous infant vaccinations given in the first year of life. In total, 319 children were included in the study. All infants received routine vaccinations at 6 weeks, 4 and 6 months of age. At 12 months of age, 212 children were vaccinated with MMR and Haemophilus influenzae type b-meningococcus C (Hib-MenC) vaccines while the remaining 99 children had not yet received these vaccines. In the MMR/Hib-MenC-vaccinated group, blood was taken 28 ± 14 days after receiving these vaccines. Antibodies against diphtheria, tetanus, pertussis [pertussis toxin (PT), filamentous hemagglutinin, pertactin], poliomyelitis (type 1, 2, 3) and 13 pneumococcal serotypes were measured. Seroprotection rates and geometric mean antibody concentrations were compared between MMR/MenC-Hib-vaccinated and MMR/MenC-Hib-naïve participants. In the final analysis, 311 children were included. Seroprotection rates were lower in MMR/Hib-MenC-vaccinated children against PT and pneumococcal serotype 19A. After adjustment for prespecified factors, MMR/Hib-MenC-vaccinated infants had significantly higher antibody concentrations against tetanus (likely explained by a boosting effect of the carrier protein, a tetanus toxoid), while for the other vaccine antigens there was no difference in antibody concentrations between the two groups. MMR vaccination given at 12 months of age in a developed country does not significantly influence antibody concentrations to heterologous vaccines received in the first year of life.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

Immunogenicity and safety of the combined vaccine for measles, mumps, and rubella isolated or combined with the varicella component administered at 3-month intervals: randomised study

BACKGROUND

Field testing required to license the combined measles, mumps, and rubella (MMR) vaccine must take into account the current recommendation of the vaccine in Brazil: first dose at 12 months and second dose at 15 months of age in combination with a varicella vaccine.

OBJECTIVES

This study aimed to evaluate the clinical consistency, immunogenicity, and reactogenicity of three batches of MMR vaccine prepared with active pharmaceutical ingredients (API) from Bio-Manguinhos, Fiocruz (MMR-Bio), and compare it to a vaccine (MMR produced by GlaxoSmithKline) with different API.

METHODS

This was a phase III, randomised, double-blind, non-inferiority study of the MMR-Bio administered in infants immunised at health care units in Pará, Brazil, from February 2015 to January 2016. Antibody levels were titrated by immunoenzymatic assays. Adverse events were recorded in diaries.

FINDINGS

Seropositivity levels after MMR-Bio were 97.6% for measles, 84.7% for mumps, and 98.0% for rubella. After the MMRV vaccine, seroconversion rates and GMT increased substantially for mumps. In contrast, approximately 35% of the children had no detectable antibodies to varicella. Systemic adverse events were more frequent than local events.

CONCLUSION

The demonstration of batch consistency and non-inferiority of the Bio-MMR vaccine completed the technology transfer. This is a significant technological achievement with implications for immunisation programs.

Cell-Mediated Immune Responses and Immunopathogenesis of Human Tick-Borne Encephalitis Virus-Infection

Tick-borne encephalitis virus (TBEV) is a flavivirus that belongs to the Flaviviridae family. TBEV is transmitted to humans primarily from infected ticks. The virus causes tick-borne encephalitis (TBE), an acute viral disease that affects the central nervous system (CNS). Infection can lead to acute neurological symptoms of significant severity due to meningitis or meningo(myelo)encephalitis. TBE can cause long-term suffering and has been recognized as an increasing public health problem. TBEV-affected areas currently include large parts of central and northern Europe as well as northern Asia. Infection with TBEV triggers a humoral as well as a cell-mediated immune response. In contrast to the well-characterized humoral antibody-mediated response, the cell-mediated immune responses elicited to natural TBEV-infection have been poorly characterized until recently. Here, we review recent progress in our understanding of the cell-mediated immune response to human TBEV-infection. A particular emphasis is devoted to studies of the response mediated by natural killer (NK) cells and CD8 T cells. The studies described include results revealing the temporal dynamics of the T cell- as well as NK cell-responses in relation to disease state and functional characterization of these cells. Additionally, we discuss specific immunopathological aspects of TBEV-infection in the CNS.

Seroepidemiology of Dengue, Zika, and Yellow Fever Viruses among Children in the Democratic Republic of the Congo

Flaviviruses such as Zika, dengue, and yellow fever cause epidemics throughout the tropics and account for substantial global morbidity and mortality. Although malaria and other vector-borne diseases have long been appreciated in Africa, flavivirus epidemiology is incompletely understood. Despite the existence of an effective vaccine, yellow fever continues to cause outbreaks and deaths, including at least 42 fatalities in the Democratic Republic of the Congo (DRC) in 2016. Here, we leveraged biospecimens collected as part of the nationally representative 2013-2014 Demographic and Health Survey in the DRC to examine serological evidence of flavivirus infection or vaccination in children aged 6 months to 5 years. Even in this young stratum of the Congolese population, we find evidence of infection by dengue and Zika viruses based on results from enzyme-linked immunosorbent assay and neutralization assay. Surprisingly, there was remarkable discordance between reported yellow fever vaccination status and results of serological assays. The estimated seroprevalences of neutralizing antibodies against each virus are yellow fever, 6.0% (95% confidence interval [CI] = 4.6-7.5%); dengue, 0.4% (0.1-0.9%); and Zika, 0.1% (0.0-0.5%). These results merit targeted, prospective studies to assess effectiveness of yellow fever vaccination programs, determine flavivirus seroprevalence across a broader age range, and investigate how these emerging diseases contribute to the burden of acute febrile illness in the DRC.

Single shot of 17D vaccine may not confer life-long protection against yellow fever

The yellow fever (YF) vaccine has been used since the 1930s to prevent YF, which is a severe infectious disease caused by the yellow fever virus (YFV), and mainly transmitted by Culicidae mosquitoes from the genera Aedes and Haemagogus . Until 2013, the World Health Organization (WHO) recommended the administration of a vaccine dose every ten years. A new recommendation of a single vaccine dose to confer life-long protection against YFV infection has since been established. Recent evidence published elsewhere suggests that at least a second dose is needed to fully protect against YF disease. Here, we discuss the feasibility of administering multiple doses, the necessity for a new and modern vaccine, and recommend that the WHO conveys a meeting to discuss YFV vaccination strategies for people living in or travelling to endemic areas.

Yellow Fever Virus, but Not Zika Virus or Dengue Virus, Inhibits T-Cell Receptor-Mediated T-Cell Function by an RNA-Based Mechanism

The Flavivirus genus within the Flaviviridae family is comprised of many important human pathogens including yellow fever virus (YFV), dengue virus (DENV), and Zika virus (ZKV), all of which are global public health concerns. Although the related flaviviruses hepatitis C virus and human pegivirus (formerly named GBV-C) interfere with T-cell receptor (TCR) signaling by novel RNA and protein-based mechanisms, the effect of other flaviviruses on TCR signaling is unknown. Here, we studied the effect of YFV, DENV, and ZKV on TCR signaling. Both YFV and ZKV replicated in human T cells in vitro; however, only YFV inhibited TCR signaling. This effect was mediated at least in part by the YFV envelope (env) protein coding RNA. Deletion mutagenesis studies demonstrated that expression of a short, YFV env RNA motif (vsRNA) was required and sufficient to inhibit TCR signaling. Expression of this vsRNA and YFV infection of T cells reduced the expression of a Src-kinase regulatory phosphatase (PTPRE), while ZKV infection did not. YFV infection in mice resulted in impaired TCR signaling and PTPRE expression, with associated reduction in murine response to experimental ovalbumin vaccination. Together, these data suggest that viruses within the flavivirus genus inhibit TCR signaling in a species-dependent manner.

Immunological considerations regarding parental concerns on pediatric immunizations

Despite the fundamental role of vaccines in the decline of infant mortality, parents may decide to decline vaccination for their own children. Many factors may influence this decision, such as the belief that the infant immune system is weakened by vaccines, and concerns have been raised about the number of vaccines and the early age at which they are administered. Studies focused on the infant immune system and its reaction to immunizations, summarized in this review, show that vaccines can overcome those suboptimal features of infant immune system that render them more at risk of infections and of their severe manifestations. In addition, many vaccines have been shown to improve heterologous innate and adaptive immunity resulting in lower mortality rates for fully vaccinated children. Thus, multiple vaccinations are necessary and not dangerous, as infants can respond to several antigens as well as when responding to single stimuli. Current immunization schedules have been developed and tested to avoid vaccine interference, improve benefits and reduce side effects compared to single administrations. The infant immune system is therefore capable, early after birth, of managing several antigenic challenges and exploits them to prompt its development.

Controvérsias sobre a ampliação das áreas com vacinação de rotina contra a febre amarela no Brasil

Resumo: Febre amarela é uma doença viral potencialmente grave, transmitida por mosquitos Haemagogus, Aedes e Sabethes. A vacinação é a medida mais importante para a sua prevenção e controle. Neste artigo, analisamos as recomendações de vacinação no Brasil, segundo a epidemiologia da doença nas últimas décadas. Considerando a facilidade de deslocamentos de suscetíveis para áreas de risco, e sua tendência de expansão, é provável que eventualmente todo o país tenha de adotar a vacinação rotineira. Porém, no processo decisório de ampliação da população candidata à vacinação, questões relacionadas à segurança vacinal têm sido destacadas. Apresentamos uma análise dos riscos e benefícios da vacinação e das estratégias para o controle da doença e prevenção da sua urbanização nas regiões onde a vacina ainda não é recomendada. Concluímos que a introdução da vacina contra a febre amarela no calendário de vacinação das crianças é uma estratégia proativa, de mais fácil operacionalização, como resposta ao aumento do número de casos de febre amarela silvestre no Brasil e tentativa de prevenção da reurbanização da doença.

Questions regarding the safety and duration of immunity following live yellow fever vaccination

INTRODUCTION

The World Health Organization (WHO) and other health agencies have concluded that yellow fever booster vaccination is unnecessary since a single dose of vaccine confers lifelong immunity. Areas covered: We reviewed the clinical studies cited by health authorities in their investigation of both the safety profile and duration of immunity for the YFV-17D vaccine and examined the position that booster vaccination is no longer needed. We found that antiviral immunity may be lost in 1-in-3 to 1-in-5 individuals within 5 to 10 years after a single vaccination and that children may be at greater risk for primary vaccine failure. The safety profile of YFV-17D was compared to other licensed vaccines including oral polio vaccine (OPV) and the rotavirus vaccine, RotaShield, which have subsequently been withdrawn from the US and world market, respectively. Expert commentary: Based on these results and recent epidemiological data on vaccine failures (particularly evident at >10 years after vaccination), we believe that current recommendations to no longer administer YFV-17D booster vaccination be carefully re-evaluated, and that further development of safer vaccine approaches should be considered.

Immunogenicity and Safety of Yellow Fever Vaccine (Stamaril) When Administered Concomitantly With a Tetravalent Dengue Vaccine Candidate in Healthy Toddlers at 12-13 Months of Age in Colombia and Peru: A Randomized Trial

BACKGROUND

Dengue and yellow fever (YF) viruses are closely related members of the Flaviviridae family. Given the inherent similarities between the YF vaccine and dengue vaccine (CYD-TDV) candidate, it is possible that the latter could interfere with the response to the licensed YF vaccine when coadministered.

METHODS

In this randomized, observer-blind, controlled, phase III trial, conducted in Colombia and Peru, 787 toddlers were administered YF vaccine concomitantly with CYD-TDV (group 1) or placebo (group 2), followed by CYD-TDV after 6 and 12 months. YF and dengue neutralizing antibody titers were determined using a 50% plaque reduction neutralization test. Noninferiority was demonstrated if the lower limit of the 2-sided 95% confidence interval of the difference in seroconversion rates [(YF + CYD-TDV) - YF alone] was greater than -10%. The safety of both vaccines was also assessed.

RESULTS

Concomitant administration of YF with either CYD-TDV or placebo yielded YF seroconversion rates of 100.0% and 99.7%, respectively. The difference in YF seroconversion rates between the 2 groups was 0.33% (95% confidence interval:0.98; 1.87), demonstrating that the immune response against YF administered concomitantly with CYD-TDV was noninferior to YF administered with placebo. After 2 injections of CYD-TDV, the percentage of participants with dengue titres ≥10 (1/dil) for the 4 dengue serotypes were 91.2%-100% for group 1 and 97.2%-100% in group 2. There were no safety concerns during the study period.

CONCLUSIONS

Concomitant administration of YF vaccine with CYD-TDV has no relevant impact on the immunogenicity or safety profile of the YF vaccine.

Immunogenicity of Yellow Fever Vaccine Coadministered With MenAfriVac in Healthy Infants in Ghana and Mali

BACKGROUND

Yellow fever (YF) is still a major public health problem in endemic regions of Africa and South America. In Africa, one of the main control strategies is routine vaccination within the Expanded Programme on Immunization (EPI). A new meningococcal A conjugate vaccine (PsA-TT) is about to be introduced in the EPI of countries in the African meningitis belt, and this study reports on the immunogenicity of the YF-17D vaccines in infants when administered concomitantly with measles vaccine and PsA-TT.

METHODS

Two clinical studies were conducted in Ghana and in Mali among infants who received PsA-TT concomitantly with measles and YF vaccines at 9 months of age. YF neutralizing antibody titers were measured using a microneutralization assay.

RESULTS

In both studies, the PsA-TT did not adversely affect the immune response to the concomitantly administered YF vaccine at the age of 9 months. The magnitude of the immune response was different between the 2 studies, with higher seroconversion and seroprotection rates found in Mali vs Ghana.

CONCLUSIONS

Immunogenicity to YF vaccine is unaffected when coadministered with PsA-TT at 9 months of age. Further studies are warranted to better understand the determinants of the immune response to YF vaccine in infancy.

CLINICAL TRIALS REGISTRATION

ISRCTN82484612 (PsA-TT-004); PACTR201110000328305 (PsA-TT-007).