Long-term immunogenicity after yellow fever vaccination in immunosuppressed and healthy individuals

Long-term immunity following yellow fever vaccination: a systematic review and meta-analysis

BACKGROUND

Long-term immunity following yellow fever vaccination remains controversial. We aimed to summarise the literature regarding the long-term protection (≥10 years) conveyed by a single dose of yellow fever vaccination.

METHODS

In this systematic review and meta-analysis, we searched 11 databases from database inception to Aug 24, 2023. We included cohort and cross-sectional studies reporting immunogenicity outcomes for children or adults who received a single dose of yellow fever vaccination 10 or more years ago. Case series and single case reports were excluded. Participants who received more than one dose of yellow fever vaccination before measurement of the outcome were excluded. Identified records were reviewed by two independent reviewers. The primary outcome of the meta-analysis was the pooled seroprotection rate. Risk of bias was assessed with the Risk Of Bias In Non-randomized Studies of Interventions tool, and the Joanna Briggs Institute tool for analytical cross-sectional studies. Studies of moderate or good quality that reported seroprotection were included for random-effects meta-analysis and stratified by endemicity and specific risk groups. The study was registered with PROSPERO, CRD42023384087.

FINDINGS

Of the 7363 articles identified by our search, 39 were eligible for inclusion for systematic review. These studies comprised 2895 individuals vaccinated 10-60 years ago. 20 studies were included in the meta-analysis. Pooled seroprotection rates were 94% (95% CI 86-99) among healthy adults in a non-endemic setting (mostly travellers) and 76% (65-85) in an endemic setting (all Brazilian studies). The pooled seroprotection rate was 47% (35-60) in children (aged 9-23 months at time of vaccination) and 61% (38-82) in people living with HIV. Reported criteria for seroprotection were highly heterogeneous.

INTERPRETATION

The gathered evidence suggests that a single dose of yellow fever vaccination provides lifelong protection in travellers. However, in people living with HIV and children (younger than 2 years), booster doses might still be required because lower proportions of vaccinees were seroprotected 10 or more years post-vaccination. Lower observed seroprotection rates among residents of endemic areas were partly explained by the use of a higher cutoff for seroprotection that was applied in Brazil. Studies from sub-Saharan Africa were scarce and of low quality; thus no conclusions could be drawn for this region.

FUNDING

None.

Recent Advancements in Mosquito-Borne Flavivirus Vaccine Development

Lately, the global incidence of flavivirus infection has been increasing dramatically and presents formidable challenges for public health systems around the world. Most clinically significant flaviviruses are mosquito-borne, such as the four serotypes of dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus and yellow fever virus. Until now, no effective antiflaviviral drugs are available to fight flaviviral infection; thus, a highly immunogenic vaccine would be the most effective weapon to control the diseases. In recent years, flavivirus vaccine research has made major breakthroughs with several vaccine candidates showing encouraging results in preclinical and clinical trials. This review summarizes the current advancement, safety, efficacy, advantages and disadvantages of vaccines against mosquito-borne flaviviruses posing significant threats to human health.

Duration of Protection After Vaccination Against Yellow Fever: A Systematic Review and Meta-Analysis

The duration of protection after a single dose of yellow fever vaccine is a matter of debate. To summarize the current knowledge, we performed a systematic literature review and meta-analysis. Studies on the duration of protection after 1 and ≥2 vaccine doses were reviewed. Data were stratified by time since vaccination. In our meta-analysis, we used random-effects models. We identified 36 studies from 20 countries, comprising more than 17 000 participants aged 6 months to 85 years. Among healthy adults and children, pooled seroprotection rates after single vaccination dose were close to 100% by 3 months and remained high in adults for 5 to 10 years. In children vaccinated before age 2 years, the seroprotection rate was 52% within 5 years after primary vaccination. For immunodeficient persons, data indicate relevant waning. The extent of waning of seroprotection after yellow fever vaccination depends on age and immune status at primary vaccination.

Long-term persistence of antibodies after diphtheria/tetanus vaccination in immunosuppressed patients with inflammatory rheumatic diseases and healthy controls

Many vaccines demonstrate high effectiveness for years. This prospective multicentre study was conducted in Switzerland to assess the long-term persistence of antibodies to the diphtheria/tetanus (dT)-vaccine in adult patients with rheumatic diseases (PRDs). 163 PRDs and 169 controls were included in the study. The median age of all participants was 50 years (range: 18-83 years) and 56% were female. After a median time interval of 16 years after vaccination, the median anti-vaccine antibody concentrations were lower in PRDs than in controls for tetanus (1.68 vs 2.01; p = 0.049) and diphtheria (0.05 vs 0.22; p = 0.002). Based on the currently accepted seroprotection threshold (antibody concentration ≥ 0.1 IU/ml), PRDs had lower proportions of short-term tetanus and diphtheria protection as demonstrated by crude odds ratios (OR) of 0.30 (p = 0.017) and OR: 0.52 (p = 0.004), respectively. After adjusting for 'age' and 'time since last dT vaccination', the strength of associations became weaker; for tetanus, borderline evidence remained for a true difference between PRDs and controls (OR: 0.36 [p = 0.098]), however, not for diphtheria (OR: 0.86 [p = 0.58]). We hypothesize that in the presence of rheumatic diseases and its immunosuppressive treatment, vaccine-specific long-lived plasma cells (LLPCs) may be diminished or competitively displaced by rheumatism-specific LLPCs, a process which may decrease the persistence of vaccine-specific antibodies. Novel studies should be designed by incorporating methodologies allowing to determine the attributable fraction of immunosuppressive/immunomodulatory medications and rheumatic disease itself on long-lasting vaccine-specific antibody persistence, as well as, further study the role of LLPCs.

Chronic Myeloid Leukemia in Children: Immune Function and Vaccinations

Children with CML need TKI treatment for many years, and the lack of knowledge about immune dysfunction with TKI has hindered routine immunizations. This review attempts to provide an overview of the effects of TKIs licensed for children (e.g., imatinib, dasatinib, and nilotinib) on immune function, as well as its implications on immunizations. We discuss surveillance strategies (e.g., immunoglobulin blood serum levels and hepatitis B reactivation) and immunizations. All inactivated vaccines (e.g., influenza, pneumococcal, and streptococcal) can be given during the treatment of CML in the chronic phase, although their efficacy may be lower. As shown in single cases of children and adults with CML, live vaccines (e.g., varicella, measles, mumps, rubella, and yellow fever) may be administered under defined circumstances with great precautions. We also highlight important aspects of COVID-19 in this patient population (e.g., the outcome of COVID-19 infection in adults with CML and in children with varying hemato-oncological diseases) and discuss the highly dynamic field of presently available different vaccination options. In conclusion, TKI treatment for CML causes humoral and cellular immune dysfunction, which is mild in most patients, and thus infectious complications are rare. Routine immunizations are important for health maintenance of children, but vaccinations for children with CML on TKI therapy should be carefully considered.

[Travel vaccinations in rheumatic diseases : Specific considerations in children and adults]

Children and adults with rheumatic diseases (RD) have a higher risk to contract infections due to the underlying disease and the frequently necessary immunosuppressive treatment (IT). The quality of life of the majority of patients with RD has remarkably improved due to IT-related reduction of inflammation. Therefore, RD patients usually have an international travel behavior similar to healthy individuals. An investigation indicated that patients with RD and IT have lower travel vaccination rates and are often less well-prepared for their trip in comparison to healthy travelers, even when visiting high risk destinations. As the risk for general and travel-acquired infections is increased for patients with RD with and without IT, pretravel consultations are important. These pretravel consultations should include recommendations addressing travel cancellation, travel modification and travel vaccinations depending on the patient's risk. Travel vaccinations include vaccinations against hepatitis A, typhoid fever, rabies, cholera, meningococcal diseases, tick-bone encephalitis, Japanese encephalitis, seasonal influenza, poliomyelitis and yellow fever. In patients with RD the indications for vaccination depend on the exposure risks, disease severity, individual travel behavior, and possible complications associated with vaccination. In the further evaluation process it is crucial to include the general health condition of the patient, the underlying RD (type and activity), duration and intensity of the IT. In general, live-attenuated vaccines are contraindicated under IT. In contrast, inactivated vaccines may be administered although reduced immunogenicity with the need for antibody measurement, special vaccine schedules or additional booster vaccinations should be considered under IT.

Impacts of High Intra- and Inter-Individual Variability in Tacrolimus Pharmacokinetics and Fast Tacrolimus Metabolism on Outcomes of Solid Organ Transplant Recipients

Tacrolimus is a first-line calcineurin inhibitor (CNI) and an integral part of the immunosuppressive strategy in solid organ transplantation. Being a dose-critical drug, tacrolimus has a narrow therapeutic index that necessitates periodic monitoring to maintain the drug’s efficacy and reduce the consequences of overexposure. Tacrolimus is characterized by substantial intra- and inter-individual pharmacokinetic variability. At steady state, the tacrolimus blood concentration to daily dose ratio (C/D ratio) has been described as a surrogate for the estimation of the individual metabolism rate, where a low C/D ratio reflects a higher rate of metabolism. Fast tacrolimus metabolism (low C/D ratio) is associated with the risk of poor outcomes after transplantation, including reduced allograft function and survival, higher allograft rejection, CNI nephrotoxicity, a faster decline in kidney function, reduced death-censored graft survival (DCGS), post-transplant lymphoproliferative disorders, dyslipidemia, hypertension, and cardiovascular events. In this article, we discuss the potential role of the C/D ratio in a noninvasive monitoring strategy for identifying patients at risk for potential adverse events post-transplant.