Japanese encephalitis vaccine for travelers: risk-benefit reconsidered

Travel vaccines-priorities determined by incidence and impact

BACKGROUND

Infectious disease epidemiology is continuously shifting. While travel has been disrupted by the COVID-19 pandemic and travel-related epidemiological research experienced a pause, further shifts in vaccine-preventable diseases (VPDs) relevant for travellers have occurred.

METHODS

We conducted a literature search on the epidemiology of travel-related VPD and synthesized data for each disease with a focus on symptomatic cases and on the impact of the respective infection among travellers, considering the hospitalization rate, disease sequela and case fatality rate. We present new data and revised best estimates on the burden of VPD relevant for decisions on priorities in travel vaccines.

RESULTS

COVID-19 has emerged to be a top travel-related risk and influenza remains high in the ranking with an estimated incidence at 1% per month of travel. Dengue is another commonly encountered infection among international travellers with estimated monthly incidence of 0.5-0.8% among non-immune exposed travellers; the hospitalized proportion was 10 and 22%, respectively, according to two recent publications. With recent yellow fever outbreaks particularly in Brazil, its estimated monthly incidence has risen to >0.1%. Meanwhile, improvements in hygiene and sanitation have led to some decrease in foodborne illnesses; however, hepatitis A monthly incidence remains substantial in most developing regions (0.001-0.01%) and typhoid remains particularly high in South Asia (>0.01%). Mpox, a newly emerged disease that demonstrated worldwide spread through mass gathering and travel, cannot be quantified regarding its travel-related risk.

CONCLUSION

The data summarized may provide a tool for travel health professionals to prioritize preventive strategies for their clients against VPD. Updated assessments on incidence and impact are ever more important since new vaccines with travel indications (e.g. dengue) have been licensed or are undergoing regulatory review.

A decision support tool for risk-benefit analysis of Japanese encephalitis vaccine in travellers

BACKGROUND

During pre-travel consultations, clinicians and travellers face the challenge of weighing the risks verus benefits of Japanese encephalitis (JE) vaccination due to the high cost of the vaccine, low incidence in travellers (~1 in 1 million), but potentially severe consequences (~30% case-fatality rate). Personalised JE risk assessment based on the travellers' demographics and travel itinerary is challenging using standard risk matrices. We developed an interactive digital tool to estimate risks of JE infection and severe health outcomes under different scenarios to facilitate shared decision-making between clinicians and travellers.

METHODS

A Bayesian network (conditional probability) model risk-benefit analysis of JE vaccine in travellers was developed. The model considers travellers' characteristics (age, sex, co-morbidities), itinerary (destination, departure date, duration, setting of planned activities) and vaccination status to estimate the risks of JE infection, the development of symptomatic disease (meningitis, encephalitis), clinical outcomes (hospital admission, chronic neurological complications, death) and adverse events following immunization.

RESULTS

In low-risk travellers (e.g. to urban areas for <1 month), the risk of developing JE and dying is low (<1 per million) irrespective of the destination; thus, the potential impact of JE vaccination in reducing the risk of clinical outcomes is limited. In high-risk travellers (e.g. to rural areas in high JE incidence destinations for >2 months), the risk of developing symptomatic disease and mortality is estimated at 9.5 and 1.4 per million, respectively. JE vaccination in this group would significantly reduce the risk of symptomatic disease and mortality (by ~80%) to 1.9 and 0.3 per million, respectively.

CONCLUSION

The JE tool may assist decision-making by travellers and clinicians and could increase JE vaccine uptake. The tool will be updated as additional evidence becomes available. Future work needs to evaluate the usability of the tool. The interactive, scenario-based, personalised JE vaccine risk-benefit tool is freely available on www.VaxiCal.com.

The evolving Japanese encephalitis situation in Australia and implications for travel medicine

The recent emergence of Japanese encephalitis in south-eastern Australia highlights the changing epidemiology of this important disease and the need for integrated surveillance to inform risk-based discussions and vaccination advice for travellers and endemic populations.

The Emergence of Travel-related Infections in Critical Care Units

Several tropical or geographically confined infectious diseases may lead to organ failure requiring management in an intensive care unit (ICU), both in endemic low- and middle-income countries where ICU facilities are increasingly being developed and in (nonendemic) high-income countries through an increase in international travel and migration. The ICU physician must know which of these diseases may be encountered and how to recognize, differentiate, and treat them. The four historically most prevalent "tropical" diseases (malaria, enteric fever, dengue, and rickettsiosis) can present with single or multiple organ failure in a very similar manner, which makes differentiation based solely on clinical signs very difficult. Specific but frequently subtle symptoms should be considered and related to the travel history of the patient, the geographic distribution of these diseases, and the incubation period. In the future, ICU physicians may also be more frequently confronted with rare but frequently lethal diseases, such as Ebola and other viral hemorrhagic fevers, leptospirosis, and yellow fever. No one could have foreseen the worldwide 2019-up to now coronavirus disease 2019 (COVID-19) crisis caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was initially spread by travel too. In addition, the actual pandemic due to SARS-CoV-2 reminds us of the actual and potential threat of (re)-emerging pathogens. If left untreated or when treated with a delay, many travel-related diseases remain an important cause of morbidity and even mortality, even when high-quality critical care is provided. Awareness and a high index of suspicion of these diseases is a key skill for the ICU physicians of today and tomorrow to develop.

Immunogenicity of a single fractional intradermal dose of Japanese encephalitis live attenuated chimeric vaccine

BACKGROUND

Japanese encephalitis (JE) is endemic in Asia and the western Pacific. Vaccination is recommended for travellers to endemic regions, but the high cost of the vaccine is a major barrier to uptake.

METHODS

A quasi-experimental, pre-post intervention clinical trial without a control group was conducted to assess the immunogenicity and safety of intradermal (ID) JE vaccine. Healthy adults (18-45 years) received one dose of 0.1 mL (20% of standard dose) ID Imojev® (JE live attenuated chimeric vaccine, Sanofi-Aventis). Adverse events following immunisation (AEFIs) were recorded 10 days post-vaccination. Blood samples were collected at baseline, 4, and 8 weeks post-vaccination. Neutralising antibodies were measured using 50% plaque reduction neutralisation test (PRNT50). Seroconversion was defined as PRNT50 titre ≥10. An in vitro study was also conducted to quantify the rate of decay of vaccine potency after reconstitution.

RESULTS

51 participants (72.6% females, median age 31 years), all non-reactive to JE virus at baseline were enrolled. Mild and moderate AEFIs were reported by 19.6% of participants; none required medical attention or interfered with normal daily activities. All participants seroconverted at 4 weeks (GMT 249.3; 95%CI:192.8-322.5) and remained seropositive at 8-weeks (GMT 135.5; 95%CI:104.5-175.6). Vaccine potency declined at a rate of 0.14 log plaque-forming units/0.5 mL per hour.

CONCLUSIONS

In healthy adults, a single 0.1 mL ID dose of Imojev was safe and immunogenic, at least in the short-term. Reconstituted vials of Imojev vaccine may not retain their potency after 6 hours. Fractional JE ID vaccination could be a cheaper yet effective alternative for short-term travellers. Further studies need to investigate the immune response in a wider age range of individuals and the long-term immunogenicity of fractional JE ID vaccines.

CLINICAL TRIALS REGISTRATION

ACTRN12621000024842.

Novel Antiviral Efficacy of Hedyotis diffusa and Artemisia capillaris Extracts against Dengue Virus, Japanese Encephalitis Virus, and Zika Virus Infection and Immunoregulatory Cytokine Signatures

Currently, there are no specific therapeutics for flavivirus infections, including dengue virus (DENV) and Zika virus (ZIKV). In this study, we evaluated extracts from the plants Hedyotis diffusa (HD) and Artemisia capillaris (AC) to determine the antiviral activity against DENV, ZIKV, and Japanese encephalitis virus (JEV). HD and AC demonstrated inhibitory activity against JEV, ZIKV, and DENV replication and reduced viral RNA levels in a dose-responsive manner, with non-cytotoxic concentration ranging from 0.1 to 10 mg/mL. HD and AC had low cytotoxicity to Vero cells, with CC₅₀ values of 33.7 ± 1.6 and 30.3 ± 1.7 mg/mL (mean ± SD), respectively. The anti-flavivirus activity of HD and AC was also consistent in human cell lines, including human glioblastoma (T98G), human chronic myeloid leukemia (K562), and human embryonic kidney (HEK-293T) cells. Viral-infected, HD-treated cells demonstrated downregulation of cytokines including CCR1, CCL26, CCL15, CCL5, IL21, and IL17C. In contrast, CCR1, CCL26, and AIMP1 were elevated following AC treatment in viral-infected cells. Overall, HD and AC plant extracts demonstrated flavivirus replication inhibitory activity, and together with immunoregulatory cytokine signatures, these results suggest that HD and AC possess bioactive compounds that may further be refined as promising candidates for clinical applications.

Molecular pathogenesis of Japanese encephalitis and possible therapeutic strategies

Japanese encephalitis virus (JEV), a single-stranded, enveloped RNA virus, is a health concern across Asian countries, associated with severe neurological disorders, especially in children. Primarily, pigs, bats, and birds are the natural hosts for JEV, but humans are infected incidentally. JEV requires a few host proteins for its entry and replication inside the mammalian host cell. The endoplasmic reticulum (ER) plays a significant role in JEV genome replication and assembly. During this process, the ER undergoes stress due to its remodelling and accumulation of viral particles and unfolded proteins, leading to an unfolded protein response (UPR). Here, we review the overall strategy used by JEV to infect the host cell and various cytopathic effects caused by JEV infection. We also highlight the role of JEV structural proteins (SPs) and non-structural proteins (NSPs) at various stages of the JEV life cycle that are involved in up- and downregulation of different host proteins and are potentially relevant for developing efficient therapeutic drugs.

Japanese encephalitis vaccine cost: a major reason to be vaccinated in Bali

Travellers, especially long term and repeat, are increasingly opting to receive vaccines in destination countries. This report summarizes the high cost of Japanese encephalitis vaccination in their home country as a barrier to pre-travel uptake.

[Travelling with children and adolescents with rheumatic diseases]

Due to the underlying disease and immunosuppressive treatment, pediatric patients with rheumatic diseases are at increased risk for (long distance) travel-related health problems. A pretravel comprehensive consultation is therefore strongly recommended. Whether a child with rheumatic disease is sufficiently fit for travel essentially depends on the disease activity, the age of the child and the intended travel destination. Depending on the level of immunosuppression, the risks for this patient group include (travel-related) infections and the possibility of disease activity flares. Of particular importance is adequate exposure prevention: standard vaccinations should be updated and indications for travel vaccinations evaluated in advance of travelling. In this context, potential contraindications, especially for live vaccines, in the case of specific immunosuppressive treatment should be considered. In the event of travel to malaria endemic areas, the necessity for chemoprophylaxis or stand-by medication must be evaluated but caution is needed regarding potential drug interactions. Detailed education about careful hand, food and contact hygiene is critical. Because photosensitivity may be increased in some rheumatic diseases and/or medications, UV protection is crucial. Barriers (clothes and mosquito nets) and age-appropriate chemical insect repellents should be used to prevent insect-borne diseases. Before start of travel, possibilities for on-site medical help in the event of disease deterioration and/or infection should be evaluated. This should be included in the assessment of the patient's ability to travel. Travelers with rheumatic disease should carry a first aid kit that includes both a sufficient supply of regular antirheumatic medication and supplemental medication in case of a disease flare. Storage conditions must be taken ínto account for some medications. Ultimately, the success of a journey depends on the planning from the perspective of the child with its specific needs.

Public health emergencies of international concern: a historic overview

RATIONALE

The International Health Regulations (IHR) have been the governing framework for global health security since 2007. Declaring public health emergencies of international concern (PHEIC) is a cornerstone of the IHR. Here we review how PHEIC are formally declared, the diseases for which such declarations have been made from 2007 to 2020 and justifications for such declarations.

KEY FINDINGS

Six events were declared PHEIC between 2007 and 2020: the 2009 H1N1 influenza pandemic, Ebola (West African outbreak 2013-2015, outbreak in Democratic Republic of Congo 2018-2020), poliomyelitis (2014 to present), Zika (2016) and COVID-19 (2020 to present). Poliomyelitis is the longest PHEIC. Zika was the first PHEIC for an arboviral disease. For several other emerging diseases a PHEIC was not declared despite the fact that the public health impact of the event was considered serious and associated with potential for international spread.

RECOMMENDATIONS

The binary nature of a PHEIC declaration is often not helpful for events where a tiered or graded approach is needed. The strength of PHEIC declarations is the ability to rapidly mobilize international coordination, streamline funding and accelerate the advancement of the development of vaccines, therapeutics and diagnostics under emergency use authorization. The ultimate purpose of such declaration is to catalyse timely evidence-based action, to limit the public health and societal impacts of emerging and re-emerging disease risks while preventing unwarranted travel and trade restrictions.

Dengue, chikungunya and Zika in GeoSentinel surveillance of international travellers: a literature review from 1995 to 2020

INTRODUCTION

GeoSentinel is a global surveillance network of travel medicine providers seeing ill-returned travellers. Much of our knowledge on health problems and infectious encountered by international travellers has evolved as a result of GeoSentinel surveillance, providing geographic and temporal trends in morbidity among travellers while contributing to improved pre-travel advice. We set out to synthesize epidemiological information, clinical manifestations and time trends for dengue, chikungunya and Zika in travellers as captured by GeoSentinel.

METHODS

We conducted a systematic literature search in PubMed on international travellers who presented with dengue, chikungunya or Zika virus infections to GeoSentinel sites around the world from 1995 until 2020.

RESULTS

Of 107 GeoSentinel publications, 42 articles were related to dengue, chikungunya and/or Zika. The final analyses and synthesis of and results presented here are based on the findings from 27 original articles covering the three arboviral diseases.

CONCLUSIONS

Dengue is the most frequent arboviral disease encountered in travellers presenting to GeoSentinel sites, with increasing trends over the past two decades. In Southeast Asia, annual proportionate morbidity increased from 50 dengue cases per 1000 ill returned travellers in non-epidemic years to an average of 159 cases per 1000 travellers during epidemic years. The highest number of travellers with chikungunya virus infections was reported during the chikungunya outbreak in the Americas and the Caribbean in the years 2013-16. Zika was first reported by GeoSentinel already in 2012, but notifications peaked in the years 2016-17 reflecting the public health emergency in the Americas at the time.

The Pretravel Consultation: Recent Updates

Estimates suggest that 43%-79% of international travelers may develop travel-related illnesses. Most such illnesses are considered mild and self-limited; however, some are life-threatening. The pretravel consultation is aimed at assessing risks for a range of illnesses, communicating these risks, and then providing individualized recommendations and interventions to minimize or manage such risks. The effective consultation is predicated on a well-prepared clinician and motivated traveler, understanding the traveler's perception of, and tolerance for, risk, and providing education applicable to the actual itinerary. Integral to the clinician's preparation is regular review of up-to-date trip-specific recommendations; country-specific information and recommendations are readily available and can now be efficiently accessed. From the infectious diseases perspective, immunizations, malaria chemoprophylaxis, insect repellent use, and travelers' diarrhea and its self-management are cornerstones of the consultation. This review focuses primarily on updating these 4 topics with recently published information relevant to adult travelers.

'More than devastating'-patient experiences and neurological sequelae of Japanese encephalitis§

BACKGROUND

Japanese encephalitis (JE), caused by the mosquito-borne JE virus, is a vaccine-preventable disease endemic to much of Asia. Travellers from non-endemic areas are susceptible if they travel to a JE endemic area. Although the risk to travellers of JE is low, the consequences may be severe.

METHODS

Here, we describe three cases of JE in British travellers occurring in 2014-15. In addition, we report, through interviews with survivors and their families, personal experiences of life after JE.

RESULTS

Three cases of JE were diagnosed in British travellers in 2014/15. One was acquired in Thailand, one in China and one in either Thailand, Laos or Cambodia. All three patients suffered severe, life-threatening illnesses, all were admitted to intensive care units and required medical evacuation back to the UK. One patient suffered a cardiac arrest during the acute stage but made a good recovery. The other two patients remain significantly paralysed and ventilator dependent. All three cases had clear indications for vaccination, and all have been left with life-changing neurological sequelae.

CONCLUSIONS

Travel health providers should be aware of the severity of JE, as well as the risk, allowing travellers to make fully informed decisions on JE vaccination.