Long-term Immune Response to Yellow Fever Vaccination in Human Immunodeficiency Virus (HIV)-Infected Individuals Depends on HIV RNA Suppression Status: Implications for Vaccination Schedule

Yellow fever neutralizing antibody seroprevalence proportion and titers in previously vaccinated adults with chronic kidney disease

Studies on yellow fever vaccine (YF) in chronic kidney disease (CKD) patients are scarce. This cross-sectional study aimed to evaluate YF neutralizing antibody seroprevalence and titers in previously vaccinated adults with CKD, on dialysis (D-CKD) or not (ND-CKD), compared to healthy persons. The micro Plaque Reduction Neutralization-Horseradish Peroxidase (μPRN-HP) test was used. Antibody titers were expressed as the reciprocal of the highest dilution that neutralized the challenge virus by 50 % (μPRN50). Seropositivity cut-off was set at ≥ 1:100. We included 153 participants: 46 ND-CKD, 50 D-CKD and 57 healthy adults. Median ages were 58.3, 55 and 52.2 years, respectively. Median time since YF vaccination was 22.3, 18.5 and 48.3 months respectively. There were no statistically significant differences in YF seroprevalence and neutralizing antibodies titers among groups: 100 % of ND-CKD; 96 % of D-CKD and 100 % of healthy participants were seropositive. Geometric mean titers (GMT) were 818.5, 683.0 and 665.5, respectively (p = 0.289).

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.

Safety of the yellow fever vaccine in people living with HIV: a longitudinal study exploring post-vaccination viremia and hematological and liver kinetics

BACKGROUND

Safety data on the yellow fever vaccine 17DD in People Living with HIV (PLWH) are limited. This study explored the occurrence of post-vaccination 17DD viremia and the kinetics of hematological and liver laboratorial parameters in PLWH and HIV-uninfected participants [HIV(-) controls].

METHODS

We conducted a secondary analysis of a longitudinal interventional trial (NCT03132311) study that enrolled PLWH and HIV(-) controls to receive a single 17DD dose and were followed at 5, 30 and 365 days after vaccination in Rio de Janeiro, Brazil. 17DD viremia (obtained throughreal-time PCR and plaque forming units' assays), hematological (neutrophils, lymphocytes and platelets counts) and liver enzymes (ALT and AST) results were assessed at baseline and Days 5 and 30 post-vaccination. Logistic regression models explored factors associated with the odds of having positive 17DD viremia. Linear regression models explored variables associated with hematological and liver enzymes results at Day 5.

RESULTS

A total of 202 PLWH with CD4 ≥ 200 cells/µL and 68 HIV(-) controls were included in the analyses. 17DD viremia was found in 20.0 % of the participants and was twice more frequent in PLWH than in HIV(-) controls (22.8% vs. 11.8 %, p-value < 0.001). Neutrophils, lymphocytes and platelets counts dropped at Day 5 and returned to baseline values at Day 30. 17DD viremia was associated with lower nadir of lymphocytes and platelets at Day 5. ALT levels did not increase post-vaccination and were not associated with 17DD viremia.

CONCLUSIONS

17DD was safe and well-tolerated in PLWH with CD4 ≥ 200 cells/µL. Post-vaccination viremia was more frequent in PLWH than in controls. Transient and self-limited decreases in lymphocytes and neutrophils occurred early after vaccination. 17DD viremia was associated with lower lymphocytes and platelets nadir after vaccination. We did not observe elevations in ALT after 17DD vaccination.

Differential gene expression of cytokines, receptors, and miRNAs in individuals living with HIV-1 and vaccinated against yellow fever

Between 2016 and 2018, Brazil faced a yellow fever (YF) outbreak, which led to an expansion of vaccination coverage. The coexistence of the YF outbreak and the HIV-1 epidemic in Brazil raised concerns regarding the immune response and vaccine effectiveness in individuals living with HIV (PLWH). The aim of this study was to investigate the immune response to YF vaccination in PLWH and HIV-uninfected individuals as controls. Transcript levels of immunomodulatory molecules, including IL-6, IL-10, IL-21, TGF-β, CD19, CD163, miR-21, miR-146, and miR-155, were measured using RTqPCR. TCD4+ cells were evaluated by cytometry, and neutralizing antibody (Nab) titers were detected by a micro plaque-reduction neutralization test. The findings of our study revealed several noteworthy observations. First, there was a notable reduction in the circulation of TCD4+ cells postvaccination. Among people living with HIV (PLWH), we observed an increase in the expression of IL-10 following vaccination, while IL-6 expression was diminished in PLWH with lower TCD4+ counts. Furthermore, we identified the downregulation of CD19 and TGF-β, along with the upregulation of IL-21 and CD163. Notably, we observed positive correlations between the levels of IL-10/IL-21, IL-10/CD163, and IL-6/CD19. Additionally, there was a positive correlation between miRNAs 146 and 155. It is important to emphasize that all participants exhibited robust neutralizing antibody responses after receiving 17DD YF vaccination. In this context, the gene expression data presented can be useful for biomarker studies of protective antibodies induced by YF vaccination. This study sheds light on immune mechanisms in individuals living with HIV and YF vaccination.

Immunogenicity and reactogenicity of yellow fever vaccine in people with HIV

OBJECTIVE

To evaluate immunogenicity and reactogenicity of yellow fever (YF) vaccine in people with HIV (PWH) compared to HIV-uninfected controls.

DESIGN

In this longitudinal interventional trial (NCT03132311), PWH with CD4 + cell count ≥200 cells/μl and controls, aged 18-59, without a previous history of YF vaccination received a single standard dose of YF vaccine (17DD) and were followed at Days 5, 30 and Year 1.

METHODS

YF-neutralization titers were measured at Days 0, 30 and Year 1 and geometric mean titers (GMT) were calculated. Adverse events (AE) and YF virus detection were measured at Days 5 and 30. Linear regression evaluated factors associated with YF-neutralization titers.

RESULTS

Two hundred and eighteen PWH and 82 controls were included. At baseline, all PWH were using antiretroviral therapy; 92.6% had undetectable HIV viral load (VL) and median CD4 + cell count was 630 cells/μl [interquartile range (IQR) 463-888]. YF vaccine was safe and there were no serious AEs. At Day 30, seroconversion was observed in 98.6% of PWH [95% confidence interval (CI): 95.6-99.6] and in 100% of controls (95% CI: 93.9-100); at Year 1, 94.0% of PWH (95% CI: 89.6-96.7) and 98.4% of controls (95% CI 90.3-99.9) were seropositive. PWH had lower GMTs than controls at Day 30 and Year 1. Baseline VL >1000 copies/ml, low CD4 + cell count and low CD4 + /CD8 + ratio were associated with lower YF-neutralization titers.

CONCLUSIONS

YF vaccine is safe in PWH with CD4 + cell count ≥200 cells/μl. YF vaccine immunogenicity is impaired in PWH, particularly among those with high VL, low CD4 + cell count and low CD4 + /CD8 + ratio at vaccination and YF-neutralization titers decays over time.

Seroconversion and persistence of neutralizing antibody response after yellow fever vaccination in patients with perinatally acquired HIV infection

OBJECTIVES

To describe the dynamics of neutralizing antibody (NAbs) response after yellow fever (YF) vaccine in young adults and adolescents with perinatally acquired HIV (pHIV).

DESIGN

A retrospective cross-sectional study at three time points around YF vaccination and a matched case-control comparison of NAbs titers several years after YF vaccination.

METHODS

We selected patients who had both documented YF vaccination and perinatally acquired HIV (n = 46). The NAbs titers were measured in plasma samples from the following three time points: during the two years before (TP0), within the year after (TP1) and >1 year after (TP2) administration of the YF vaccine. The impact of perinatal infection was assessed by comparing pHIV YF vaccinees with 44 controls infected with HIV during adulthood.

RESULTS

The median time between the YF vaccine and TP1 and TP2 was 123 days and 7.3 years, respectively. After YF vaccination, 85% of vaccinees experienced seroconversion. The proportion of pHIV patients with NAbs above the protective threshold was stable between TP1 and TP2 (91% and 86%, respectively) but levels of NAbs decreased significantly between TP1 and TP2 (P = 0.0122). The case-control analysis found slightly higher geometrical mean titers (GMT) in pHIV than patients infected during adulthood.

CONCLUSIONS

Patients with pHIV showed high seroconversion rate and NAbs persistence at levels above the protective threshold after first YF vaccination. However, a decline in antibody levels over time suggests that at least one revaccination may be necessary to maintain circulating antibodies, contrary to recommendations for the general population.

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.

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.

Immunogenicity and safety of primary fractional-dose yellow fever vaccine in autoimmune rheumatic diseases

Background

Brazil faced a yellow fever(YF) outbreak in 2016–2018 and vaccination was considered for autoimmune rheumatic disease patients(ARD) with low immunosuppression due to YF high mortality.

Objective

This study aimed to evaluate, prospectively for the first time, the short-term immunogenicity of the fractional YF vaccine(YFV) immunization in ARD patients with low immunossupression.

Methods and Results

A total of 318 participants(159 ARD and 159 age- and sex-matched healthy controls) were vaccinated with the fractional-dose(one fifth) of 17DD-YFV. All subjects were evaluated at entry(D0), D5, D10, and D30 post-vaccination for clinical/laboratory and disease activity parameters for ARD patients. Post-vaccination seroconversion rate(83.7%vs.96.6%, p = 0.0006) and geometric mean titers(GMT) of neutralizing antibodies[1143.7 (95%CI 1012.3–1292.2) vs.731 (95%CI 593.6–900.2), p<0.001] were significantly lower in ARD compared to controls. A lower positivity rate of viremia was also identified for ARD patients compared to controls at D5 (53%vs.70%, p = 0.005) and the levels persisted in D10 for patients and reduced for controls(51%vs.19%, p = 0.0001). The viremia was the only variable associated with seroconvertion. No serious adverse events were reported. ARD disease activity parameters remained stable at D30(p>0.05).

Conclusion

Fractional-dose 17DD-YF vaccine in ARD patients resulted in a high rate of seroconversion rate(>80%) but lower than controls, with a longer but less intense viremia. This vaccine was immunogenic, safe and did not induce flares in ARD under low immunosuppression and may be indicated in YF outbreak situations and for patients who live or travel to endemic areas.

Trial registration

This clinical trial was registered with Clinicaltrials.gov (#NCT03430388).

Yellow fever is a viral hemorragic fever with high mortality rate and the vaccine is a remarkably successful way of preventing it. As a live attenuated virus vaccine, it is not recommended for rheumatic and other immunossupressed patients in general. However, in an outbreak scenario, the risk of dying of the disease can be higher than the risk of a vaccine serious adverse event. In 2018, the fractional-dose yellow fever vaccine was offered to the hospital employees and to the rheumatic patients without or with low immunossupression therapy in Hospital das Clinicas of University of São Paulo, during the yellow fever outbreak in São Paulo, Brazil. In order to optimize the yellow fever vaccine (YFV) supply, the fractional-dose (corresponding to one fifth) was adopted in the public vaccine campaign.

This is the first study evaluating the primary vaccination with fractional-dose YFV in autoimmune rheumatic diseases(ARD) patients (n = 159) under low immunosuppression. Most vaccinated participants were able to produce enough neutralizing antibodies to be protected against yellow fever (seroconversion rate of 84% versus 96% in healthy controls). Neither activity of the rheumatic disease or serious adverse event was identified during the 30 days of followup after the vaccination.

The Present and Future of Yellow Fever Vaccines

The disease yellow fever (YF) is prevented by a live-attenuated vaccine, termed 17D, which has been in use since the 1930s. One dose of the vaccine is thought to give lifelong (35+ years) protective immunity, and neutralizing antibodies are the correlate of protection. Despite being a vaccine-preventable disease, YF remains a major public health burden, causing an estimated 109,000 severe infections and 51,000 deaths annually. There are issues of supply and demand for the vaccine, and outbreaks in 2016 and 2018 resulted in fractional dosing of the vaccine to meet demand. The World Health Organization (WHO) has established the “Eliminate Yellow Fever Epidemics” (EYE) initiative to reduce the burden of YF over the next 10 years. As with most vaccines, the WHO has recommendations to assure the quality, safety, and efficacy of the YF vaccine. These require the use of live 17D vaccine only produced in embryonated chicken eggs, and safety evaluated in non-human primates only. Thus, any second-generation vaccines would require modification of WHO recommendations if they were to be used in endemic countries. There are multiple second-generation YF vaccine candidates in various stages of development that must be shown to be non-inferior to the current 17D vaccine in terms of safety and immunogenicity to progress through clinical trials to potential licensing. The historic 17D vaccine continues to shape the global vaccine landscape in its use in the generation of multiple licensed recombinant chimeric live vaccines and vaccine candidates, in which its structural protein genes are replaced with those of other viruses, such as dengue and Japanese encephalitis. There is no doubt that the YF 17D live-attenuated vaccine will continue to play a role in the development of new vaccines for YF, as well as potentially for many other pathogens.

Longitudinal analysis shows durable and broad immune memory after SARS-CoV-2 infection with persisting antibody responses and memory B and T cells

Ending the COVID-19 pandemic will require long-lived immunity to SARS-CoV-2. Here, we evaluate 254 COVID-19 patients longitudinally up to 8 months and find durable broad-based immune responses. SARS-CoV-2 spike binding and neutralizing antibodies exhibit a bi-phasic decay with an extended half-life of >200 days suggesting the generation of longer-lived plasma cells. SARS-CoV-2 infection also boosts antibody titers to SARS-CoV-1 and common betacoronaviruses. In addition, spike-specific IgG+ memory B cells persist, which bodes well for a rapid antibody response upon virus re-exposure or vaccination. Virus-specific CD4+ and CD8+ T cells are polyfunctional and maintained with an estimated half-life of 200 days. Interestingly, CD4+ T cell responses equally target several SARS-CoV-2 proteins, whereas the CD8+ T cell responses preferentially target the nucleoprotein, highlighting the potential importance of including the nucleoprotein in future vaccines. Taken together, these results suggest that broad and effective immunity may persist long-term in recovered COVID-19 patients.

Longitudinal analysis shows durable and broad immune memory after SARS-CoV-2 infection with persisting antibody responses and memory B and T cells

Ending the COVID-19 pandemic will require long-lived immunity to SARS-CoV-2. Here, we evaluate 254 COVID-19 patients longitudinally up to eight months and find durable broad-based immune responses. SARS-CoV-2 spike binding and neutralizing antibodies exhibit a bi-phasic decay with an extended half-life of >200 days suggesting the generation of longer-lived plasma cells. SARS-CoV-2 infection also boosts antibody titers to SARS-CoV-1 and common betacoronaviruses. In addition, spike-specific IgG+ memory B cells persist, which bodes well for a rapid antibody response upon virus re-exposure or vaccination. Virus-specific CD4+ and CD8+ T cells are polyfunctional and maintained with an estimated half-life of 200 days. Interestingly, CD4+ T cell responses equally target several SARS-CoV-2 proteins, whereas the CD8+ T cell responses preferentially target the nucleoprotein, highlighting the potential importance of including the nucleoprotein in future vaccines. Taken together, these results suggest that broad and effective immunity may persist long-term in recovered COVID-19 patients.

No need for secondary Pneumocystis jirovecii pneumonia prophylaxis in adult people living with HIV from Europe on ART with suppressed viraemia and a CD4 cell count greater than 100 cells/µL

INTRODUCTION

Since the beginning of the HIV epidemic in resource-rich countries, Pneumocystis jirovecii pneumonia (PjP) is one of the most frequent opportunistic AIDS-defining infections. The Collaboration of Observational HIV Epidemiological Research Europe (COHERE) has shown that primary Pneumocystis jirovecii Pneumonia (PjP) prophylaxis can be safely withdrawn in patients with CD4 counts of 100 to 200 cells/µL if plasma HIV-RNA is suppressed on combination antiretroviral therapy. Whether this holds true for secondary prophylaxis is not known, and this has proved difficult to determine due to the much lower population at risk.

METHODS

We estimated the incidence of secondary PjP by including patient data collected from 1998 to 2015 from the COHERE cohort collaboration according to time-updated CD4 counts, HIV-RNA and use of PjP prophylaxis in persons >16 years of age. We fitted a Poisson generalized additive model in which the smoothed effect of CD4 was modelled by a restricted cubic spline, and HIV-RNA was stratified as low (<400), medium (400 to 10,000) or high (>10,000copies/mL).

RESULTS

There were 373 recurrences of PjP during 74,295 person-years (py) in 10,476 patients. The PjP incidence in the different plasma HIV-RNA strata differed significantly and was lowest in the low stratum. For patients off prophylaxis with CD4 counts between 100 and 200 cells/µL and HIV-RNA below 400 copies/mL, the incidence of recurrent PjP was 3.9 (95% CI: 2.0 to 5.8) per 1000 py, not significantly different from patients on prophylaxis in the same stratum (1.9, 95% CI: 0.1 to 3.7).

CONCLUSIONS

HIV viraemia importantly affects the risk of recurrent PjP. In virologically suppressed patients on ART with CD4 counts of 100 to 200/µL, the incidence of PjP off prophylaxis is below 10/1000 py. Secondary PjP prophylaxis may be safely withheld in such patients. While European guidelines recommend discontinuing secondary PjP prophylaxis only if CD4 counts rise above 200 cells/mL, the latest US Guidelines consider secondary prophylaxis discontinuation even in patients with a CD4 count above 100 cells/µL and suppressed viral load. Our results strengthen and support this US recommendation.

Immunogenicity and duration of protection after yellow fever vaccine in people living with human immunodeficiency virus: a systematic review

BACKGROUND

We lack the rationale on which to base the development of a yellow fever (YF) vaccination schedule for people living with human immunodeficiency virus (PLWHIV).

OBJECTIVES

To report on the current evidence regarding the seroconversion rate and the duration of humoral protection after YF vaccine, as well as the impact of revaccination in PLWHIV.

DATA SOURCES

MEDLINE, Google Scholar, LILACS and Cochrane CENTRAL were searched.

METHODS

We selected studies on PLWHIV of all ages (including perinatally HIV-infected patients) and all settings (YF endemic and non-endemic zones). Intervention investigated was vaccination against YF, at least once after the HIV diagnosis. The research questions were the seroconversion rate, duration of humoral immunity after YF vaccine and impact of revaccination in PLWHIV. Selected studies were assessed for quality using the Newcastle-Ottawa scale.

RESULTS

Ten, six and six studies were selected for the systematic review of each question, respectively. Only one study addressed the first question in perinatally HIV-infected children. The quality of the studies was assessed as Poor (n = 16), Fair (n = 2) or Good (n = 4). A meta-analysis demonstrated that 97.6% (95% CI 91.6%-100%) of the included population seroconverted. Between 1 and 10 years after YF vaccine, reported persistence of neutralizing antibodies was 72% (95% CI 53.6%-91%), and it was 62% (95% CI 45.4%-78.6%) more than 10 years after YF vaccine. No conclusions could be drawn on impact of revaccination because of the small number of patients.

CONCLUSIONS

The current evidence regarding seroconversion rate, duration of humoral protection after YF vaccine and impact of revaccination in PLWHIV is limited by the low number and quality of studies. Based on the presently available data, it is difficult to rationally develop yellow fever vaccination guidelines for PLWHIV.

A clinician's perspective on yellow fever vaccine-associated neurotropic disease

Yellow fever (YF) causes high fever, liver dysfunction, renal failure, hypercoagulopathy and platelet dysfunction and can lead to shock and death with a case-fatality ratio of 20-50%. YF vaccination results in long-lasting protective immunity. Serious adverse events (SAEs), such as YF vaccine-associated neurotropic disease (YEL-AND) are rare. We present a case of a 56-year-old Caucasian man with fever, headache, cognitive problems at the emergency department. He received a primary YF vaccination 4 weeks prior to symptom onset. Cerebrospinal fluid tested positive (POS) for YF virus by reverse transcriptase polymerase chain reaction and confirmed diagnosis of YEL-AND. The patient recovered with symptomatic treatment. We reviewed published clinical reports on YEL-AND indexed for MEDLINE. We identified and analyzed 53 case reports. Forty-five patients were male and eight were female. Twenty-nine cases met criteria for definite YEL-AND and twenty-four for suspected YEL-AND according to YF Vaccine Safety Working Group. We applied the Brighton Collaboration diagnostic criteria to assess the diagnostic accuracy of the clinical diagnoses and found meningoencephalitis in 38 reported YEL-AND cases, Guillain Barré Syndrome (GBS) in seven, Acute Disseminated Encephalomyelitis (ADEM) in six and myelitis in five. Thirty-five patients recovered or improved; however, not all cases had a complete follow-up. The prognosis of YEL-AND presenting with GBS, ADEM or myelitis was poor. Fourteen patients received therapy (corticosteroids, intravenous immunoglobulins and/or plasmapheresis). In conclusion, YF vaccine-associated neurotropic disease is a very rare but SAE after YF vaccination. We described a case of YEL-AND and propose a standardized clinical workup of this condition based on a review of the literature. Centralized registration of complications of YF vaccination is encouraged.

Yellow fever control: current epidemiology and vaccination strategies

Yellow fever (YF) outbreaks continue, have expanded into new areas and threaten large populations in South America and Africa. Predicting where epidemics might occur must take into account local mosquito populations and specific YF virus strain, as well as ecoclimatic conditions, sociopolitical and demographic factors including population size, density, and mobility, and vaccine coverage. Populations of Aedes aegypti and Aedes albopictus from different regions vary in susceptibility to and capacity to transmit YF virus. YF virus cannot be eliminated today because the virus circulates in animal reservoirs, but human disease could be eliminated with wide use of the vaccine. WHO EYE (Eliminate Yellow Fever Epidemics) is a welcome plan to control YF, with strategies to be carried out from 2017 to 2026: to expand use of YF vaccine, to prevent international spread, and to contain outbreaks rapidly. YF vaccination is the mainstay in controlling YF outbreaks, but global supply is insufficient. Therefore, dose-sparing strategies have been proposed including fractional dosing and intradermal administration. Fractional dosing has been effectively used in outbreak control but currently does not satisfy International Health Regulations; special documentation is needed for international travel. Vector control is another facet in preventing YF outbreaks, and novel methods are being considered and proposed.

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

BACKGROUND

The live-attenuated yellow fever vaccine (YFV) is generally contraindicated in immunosuppressed patients. Our aim was to investigate if immunosuppressive therapy impairs the long-term protection against yellow fever virus in patients who had received YFV prior to the start of their immunosuppressive therapy.

METHODS

Our study examined 35 healthy individuals and 40 immunosuppressed patients with autoimmune diseases or organ transplants. All individuals had received YFV prior to the onset of their immunosuppression. We analysed the long-term influence of the immunosuppressive therapy on the YFV protective immunity by measuring neutralising antibodies (NA) with the Plaque Reduction Neutralisation Test (PRNT). We assessed risk factors for a negative PRNT result (titre below 1: 10) and their influence on the magnitude of the NA.

RESULTS

A median time interval of 21.1 years (interquartile range 14.4-31.3 years) after the YFV in all patients, a total of 35 immunosuppressed patients (88%) were seropositive (PRNT ≥ 1:10) compared to 31 patients (89%) in the control group. The geometric mean titres of NA did not differ between the groups. The duration of an underlying rheumatic disease was the only risk factor found for a lower magnitude of NA. An insufficient level of NA was found in nine subjects (12%) who had received a single dose of YFV (in one subject, the number of YFV doses was unknown).

CONCLUSION

The use of an immunosuppressive drug started after the administration of the YFV did not affect long-term persistence of NA. A second dose of YFV may be necessary to secure long-term immunity.

Travel vaccination recommendations and infection risk in HIV-positive travellers

BACKGROUND

With the advent of highly active antiretroviral drugs for the treatment of human immunodeficiency virus (HIV) it has become possible for people with HIV to travel to destinations that may place them at risk of a number of infectious diseases. Prevention of infections by vaccination is therefore of paramount importance for these travellers. However, vaccine responsiveness in HIV-positive individuals is not infrequently reduced compared to HIV-negative individuals. An understanding of the expected immune responses to vaccines in HIV-positive travellers is therefore important in planning the best approach to a pretravel consultation.

METHODS

A PubMed search was performed on HIV or acquired immune deficiency syndrome together with a search for specific vaccines. Review of the literature was performed to develop recommendations on vaccinations for HIV-positive travellers to high-risk destinations.

RESULTS

The immune responses to several vaccines are reduced in HIV-positive people. In the case of vaccines for hepatitis A, hepatitis B, influenza, pneumococcus, meningococcus and yellow fever there is a good body of data in the literature showing reduced immune responsiveness and also to help guide appropriate vaccination strategies. For other vaccines like Japanese encephalitis, rabies, typhoid fever, polio and cholera the data are not as robust; however, it is still possible to gain some understanding of the reduced responses seen with these vaccines.

CONCLUSION

This review provides a summary of the immunological responses to commonly used vaccines for the HIV-positive travellers. This information will help guide travel medicine practitioners in making decisions about vaccination and boosting of travellers with HIV.