Expert opinion on vaccination of travelers against Japanese encephalitis

Japanese Encephalitis Vaccine Acceptance and Strategies for Travelers: Insights from a Scoping Review and Practitioners in Endemic Countries

Japanese encephalitis (JE) remains the cause of vaccine-preventable encephalitis in individuals living in endemic areas and international travelers. Although rare, the disease's high fatality rate emphasizes the need for effective immunization. This review aims to provide updated data on the JE burden between 2017 and 2023, vaccine acceptance, and vaccine strategies for travelers. We prospectively identified studies, using MEDLINE and PubMed, published through 2023. JE incidence has decreased in local populations and remains low among travelers from non-endemic countries. The local JE risk cannot be utilized to determine traveler risk. Adult travelers naïve to JEV infection or immunization may be at potentially higher risk. The JE vaccine acceptance rates among international travelers visiting JE endemic areas range from 0.2% to 28.5%. The cost of the vaccine and low risk perception could be barriers to JE vaccination. For travelers, an accelerated two-dose regimen of inactivated Vero cell JE vaccine (JE-VC) or a single dosage of live attenuated JE vaccine (JE-LV) may be an option. In conclusion, the JE burden among residents and travelers is lower, but the risk is not negligible. Practitioners should prioritize sharing knowledge, increasing awareness, and promoting vaccinations and preventive measures to reduce tourists' risk of JE along their journey.

Flavivirus vaccines: Virus-like particles and single-round infectious particles as promising alternatives

The genus flavivirus of the Flaviridae family includes several human pathogens, like dengue, Zika, Japanese encephalitis, and yellow fever virus. These viruses continue to be a significant threat to human health. Vaccination remains the most useful approach to reduce the impact of flavivirus fever. However, currently available vaccines can induce severe side effects or have low effectiveness. An alternative is the use of recombinant vaccines, of which virus-like particles (VLP) and single-round infectious particles (SRIP) are of especial interest. VLP consist of the virus structural proteins produced in a heterologous system that self-assemble in a structure almost identical to the native virus. They are highly immunogenic and have been effective vaccines for other viruses for over 30 years. SRIP are promising vaccine candidates, as they induce both cellular and humoral responses, as viral proteins are expressed. Here, the state of the art to produce both types of particles and their use as vaccines against flaviviruses are discussed. We summarize the different approaches used for the design and production of flavivirus VLP and SRIP, the evidence for their safety and efficacy, and the main challenges for their use as commercial vaccines.

[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.

[Travel vaccinations for certain groups of persons]

The number of international travelers has been continuously increasing in recent decades. Among travelers, there are more and more people at an increased risk for acquiring diseases that could be prevented by vaccines or for the development of a severe course of disease. Risk groups in travel medicine are senior travelers, children, pregnant and breast-feeding women, persons with pre-existing medical conditions, and persons who visit their friends and relatives abroad (VFR). Individuals in these groups require attention during pretravel advice consultations, particularly with regards to recommended vaccinations. On the other hand, for some risk groups, particular vaccines cannot be given for safety reasons or because the response to vaccines is reduced. Not all risk groups or each vaccine have sufficient evidence available, so each patient's risks and benefits must be weighed during pretravel consultation. In this article, the particularities for each risk group with respect to pretravel immunization are highlighted.

'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.

Improving immunization strategies in patients with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) are susceptible to varieties of opportunistic infections due to immunological changes in the setting of their disease and drug-induced immunosuppression. Even though numerous infections can be prevented by vaccine, vaccination in IBD patients is inadequate. Data showed only 9% were vaccinated against pneumococcal infection and 28% described commonly receiving influenza vaccine. This review article discusses the recent immunizations against influenza virus; pneumococcal infection; human papilloma virus; tetanus, diphtheria and pertussis; measles, mumps and rubella; varicella zoster; and herpes zoster for individuals diagnosed with IBD and those patients with drug-related immunosuppression. In addition, this review discusses concerns about IBD patients planning to travel abroad. Immunization status and screening for opportunistic infection need to be addressed in IBD patients at the time of diagnosis and they should be vaccinated accordingly. Generally, standard vaccination strategies should be pursued in IBD patients, although live vaccines should be avoided while they are not immunocompetent.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

Risk assessment for Japanese encephalitis vaccination

Japanese encephalitis (JE) is the most commonly diagnosed viral encephalitis in Asia. JE is caused by a virus called JE virus (JEV), a member of the genus Flavivirus, family Flaviviridae, and is transmitted by Culex mosquitoes. Neutralising antibody to JEV protects against JE, and can be induced by vaccination. JE is a potential threat to travellers to endemic areas, which are most of South and Southeast Asia and some Pacific Islands. The risk of JE can be expected to increase with increasing mosquito exposure and time spent in regions and seasons of active transmission. JE is very rare in travellers, but mortality is high, around 1 in 3, and there is a high rate of lasting neurological damage. JE can therefore be a profoundly life changing event for a traveller. Travellers and their healthcare providers need to balance the low risk of disease against the very high severity of disease if it does occur. In order to make an informed decision, the severity of JE disease should be carefully explained to travellers to Asia.

The changing epidemiology of Japanese encephalitis and New data: the implications for New recommendations for Japanese encephalitis vaccine

The epidemiology of Japanese Encephalitis and risk to the traveler has changed and continues to evolve. The spread of Japanese Encephalitis virus into new environments, changes in agricultural practice and animal vectors, climate change, peri-urban growth, changes in international travel to Asia, personal risk factors, mosquito vector free transmission, interactions with other flaviviruses and better information on infections without encephalitis and other factors make Japanese Encephalitis an underappreciated risk. There has also been a change in the incidence of Japanese Encephalitis cases that questions the current travel duration and geographic based recommendations. A safe, effective vaccine (Ixiaro) that may be administered in a short course regimen is now available in the United States without the risks of the previous vaccine. However, the vaccine is significantly underutilized. These changes in the epidemiology and new data on the risks of the Japanese Encephalitis virus require a review of the practice guidelines and expert recommendations that do not reflect the current state of knowledge.

Mapping the spatial distribution of the Japanese encephalitis vector, Culex tritaeniorhynchus Giles, 1901 (Diptera: Culicidae) within areas of Japanese encephalitis risk

BACKGROUND

Japanese encephalitis (JE) is one of the most significant aetiological agents of viral encephalitis in Asia. This medically important arbovirus is primarily spread from vertebrate hosts to humans by the mosquito vector Culex tritaeniorhynchus. Knowledge of the contemporary distribution of this vector species is lacking, and efforts to define areas of disease risk greatly depend on a thorough understanding of the variation in this mosquito's geographical distribution.

RESULTS

We assembled a contemporary database of Cx. tritaeniorhynchus presence records within Japanese encephalitis risk areas from formal literature and other relevant resources, resulting in 1,045 geo-referenced, spatially and temporally unique presence records spanning from 1928 to 2014 (71.9% of records obtained between 2001 and 2014). These presence data were combined with a background dataset capturing sample bias in our presence dataset, along with environmental and socio-economic covariates, to inform a boosted regression tree model predicting environmental suitability for Cx. tritaeniorhynchus at each 5 × 5 km gridded cell within areas of JE risk. The resulting fine-scale map highlights areas of high environmental suitability for this species across India, Nepal and China that coincide with areas of high JE incidence, emphasising the role of this vector in disease transmission and the utility of the map generated.

CONCLUSIONS

Our map contributes towards efforts determining the spatial heterogeneity in Cx. tritaeniorhynchus distribution within the limits of JE transmission. Specifically, this map can be used to inform vector control programs and can be used to identify key areas where the prevention of Cx. tritaeniorhynchus establishment should be a priority.

Preventative Care in the Patient with Inflammatory Bowel Disease: What Is New?

Patients with inflammatory bowel disease (IBD) do not receive routine preventative care at the same rate as general medical patients. This patient population is at increased risk of vaccine preventable illness such as influenza and pneumococcal pneumonia. This review will discuss health maintenance needs and preventative care issues in patients with IBD.

Japanese encephalitis: a review of clinical guidelines and vaccine availability in Asia

Travelers to Asia are at risk for acquiring Japanese Encephalitis (JEV), an arbovirus with high rates of morbidity and mortality. Recent advances in vaccination resulting in vaccines with low rates of side effects have strengthened the rationale to vaccinate more travelers to this region, as reflected in many updated national guidelines for prevention of disease in travelers. Vaccines however still require a complex pre-travel schedule and are costly, often leading to a requirement or desire for a vaccination option in the destination country. We explore current national guidelines for prevention of Japanese Encephalitis and seek to provide information on availability of JEV vaccines in various Asian countries.

Short-Term Immunogenicity and Safety of an Accelerated Pre-Exposure Prophylaxis Regimen With Japanese Encephalitis Vaccine in Combination With a Rabies Vaccine: A Phase III, Multicenter, Observer-Blind Study

BACKGROUND

The current Japanese encephalitis (JE) vaccination regimen requires two doses and 4 weeks to complete, which may not always be feasible for travelers on short notice. One of the primary endpoints of this phase III study was to demonstrate noninferiority of immune responses to a JE vaccine following an accelerated 1-week JE vaccination regimen administered concomitantly with a rabies vaccine as compared to a standard 4-week JE regimen alone. In addition, the immunogenicity of concomitant administration of JE and rabies vaccines following standard regimens was evaluated, as well as the tolerability and safety profile of each regimen under study.

METHODS

Healthy adults aged 18 to ≤65 years were randomized to regimens with an accelerated or standard schedule: JE+rabies-standard (n = 167), JE+rabies-accelerated (n = 217) or JE-standard (n = 56). Immunogenicity against JE antigen was assessed by a 50% plaque reduction neutralization test (PRNT50 ) titer of ≥1 : 10, measured 28 days after last active vaccine (LAV) administration. Solicited reactions were collected 7 days after each vaccination; spontaneously reported adverse events (AEs) and serious AEs were monitored up to day 57. This paper reports results until day 57.

RESULTS

Noninferiority of immune responses was established for JE+rabies-accelerated compared to the JE-standard regimen 28 days after LAV administration. Overall, 99% and 100% of subjects in the JE+rabies-accelerated and JE-standard groups, respectively, achieved PRNT50 titers of ≥1 : 10 at 28 days after LAV administration. No impact of concomitant rabies vaccination was observed either on immune responses or on the safety profile of the JE vaccine.

CONCLUSIONS

This was the first randomized, controlled trial that demonstrated the strong short-term immunogenicity of a new, accelerated, 1-week JE-regimen, which was noninferior to that of the standard regimen, with a satisfactory tolerability and safety profile and no impact of concomitant rabies vaccination. This accelerated regimen, if licensed, could potentially be a valid alternative for individuals requiring a primary series of JE vaccination and rabies pre-exposure prophylaxis on short notice.

An overview of travel-associated central nervous system infectious diseases: risk assessment, general considerations and future directions

Nervous system infections are among the most important diseases in travellers. Healthy travellers might be exposed to infectious agents of central nervous system, which may require in-patient care. Progressive course is not uncommon in this family of disorders and requires swift diagnosis. An overview of the available evidence in the field is, therefore, urgent to pave the way to increase the awareness of travel-medicine practitioners and highlights dark areas for future research. In November 2013, data were collected from PubMed, Scopus, and Web of Knowledge (1980 to 2013) including books, reviews, and peer-reviewed literature. Works pertained to pre-travel care, interventions, vaccinations related neurological infections were retrieved. Here we provide information on pre-travel care, vaccination, chronic nervous system disorders, and post-travel complications. Recommendations with regard to knowledge gaps, and state-of-the-art research are made. Given an increasing number of international travellers, novel dynamic ways are available for physicians to monitor spread of central nervous system infections. Newer research has made great progresses in developing newer medications, detecting the spread of infections and the public awareness. Despite an ongoing scientific discussion in the field of travel medicine, further research is required for vaccine development, state-of-the-art laboratory tests, and genetic engineering of vectors.

Japanese encephalitis in a French traveler to Nepal

Japanese encephalitis is frequent in Asia, with a severe prognosis, but rare in travelers. Culex mosquitoes transmit Japanese encephalitis virus. Risk factors are destination, duration of stay, summer and fall seasons, outdoor activities, and type of accommodation. We report the case of a French traveler to Nepal with neutralization-based serological confirmed Japanese encephalitis. He presented classical clinical (viral syndrome before an encephalitis status with behavioral disorder, global hypotonia, mutism, movement disorders, seizure, and coma), radiological (lesions of thalami, cortico-spinal tracts, and brainstem) and biological features (lymphocytic meningitis). Nowadays, the presence of Japanese encephalitis virus in Nepal, including mountain areas, is established but Japanese encephalitis remains rare in travelers returning from this area and neurologist physicians need to become familiar with this. We recommend vaccination for travelers spending a long period of time in Nepal and having at-risk outdoor activities.

Expatriates: special considerations in pretravel preparation

Expatriates comprise a diverse set of travelers who face unique medical, psychiatric, and non-health-related risks as a result of increased exposure to host country environment and associated lifestyle. Expatriates have an increased risk of developing malaria, gastrointestinal disorders, latent tuberculosis, vaccine-preventable infections, and psychological disorders, when compared with other travelers, yet the majority of existing pretravel guidelines have been designed to suit the needs of nonexpatriates. Although greater interest in expatriate health issues has led to improved characterization of illness in this population, expatriate-specific risk mitigation strategies-including modifications to chemoprophylaxis recommendations, limiting tuberculosis exposure, and prevention of occupational or sexual blood-borne virus transmission-are poorly described. Occupations and destinations affect travel-related disease risk and should inform the pretravel consultation.

Low risk of Japanese encephalitis in short-term Australian travelers to Asia

The risk of Japanese encephalitis (JE) in travelers is unknown. In this prospective study, we investigated the incidence of JE in 387 short-term Australian travelers visiting Asia over a 32-month period from August 2007 to February 2010 by performing pre- and post-travel antibody testing. No travelers were infected with JE virus during travel, indicating a low risk of infection for short-term travelers.

Allergy to IXIARO and BIKEN Japanese encephalitis vaccines

We describe an allergic reaction to both mouse brain-derived BIKEN and Vero cell-derived IXIARO Japanese encephalitis (JE) vaccines in a single traveler. In the absence of the stabilizers and murine proteins in the BIKEN vaccine, a common factor in both vaccines is likely to be responsible, possibly JE virus antigen itself.

Viruses acquired abroad: what does the primary care physician need to know?

BACKGROUND

Viral infections are imported by travelers and immigrants from tropical or subtropical regions. The primary care physician should be able to include these diseases in the differential diagnosis of various clinical conditions.

METHODS

This review is based on pertinent articles retrieved by a selective search of the literature, including guidelines from Germany and abroad.

RESULTS

The available data on imported viral infections in Germany constitute low-level evidence, because most such infections are not reportable in this country. Useful data have, however, been collected by international surveillance networks. Imported viral infections usually present with fever, often also with a rash and elevated transaminases. An average of 230 cases occur in Germany each year; the most common diagnosis among them is dengue fever. An imported viral infection should also be included in the differential diagnosis of fever with arthralgia, as chikungunya virus causes an average of 38 such cases per year. On the other hand, in the past two years, there have been only five cases of imported viral infections causing encephalitis (West Nile virus and Japanese encephalitis virus).

CONCLUSION

The primary care physician should take a thorough history so that specifically targeted laboratory tests can be ordered as soon as possible. If the suspicion of an imported viral infection is confirmed, the patient should be transferred to a specialized treatment center.

A case of Japanese encephalitis virus infection acquired during a trip in Thailand

A case of Japanese encephalitis virus (JEV) infection is reported in a young traveler returning from Thailand. Clinical suspicion of JEV in travelers returning from endemic areas with neurologic symptoms is warranted. Confirmation of the diagnosis is complex and requires specialized laboratory services. Individualized advice on the costs and benefits of vaccination is recommended.

Japanese encephalitis in a Danish short-term traveler to Cambodia

We present a recent case of Japanese encephalitis in a Danish male traveler to Cambodia, who we believe is the second Danish case within the last 15 years. Although both this and a number of other travel-related cases occurred in short-term travelers, change in vaccination recommendations is not recommended.

Inflammatory bowel disease in travelers: Choosing the right vaccines and check-ups

The majority of patients with inflammatory bowel disease (IBD) achieve good control of the inflammatory activity using available therapies. When remission is achieved and quality of life recovered, a considerable proportion of IBD patients express their desire to travel abroad, be it for business, academic or leisure purposes. Their physicians should help and encourage them whenever possible. However, preventive measures are warranted to minimize the risk, since IBD patients are exposed to the same infections affecting the general population, plus opportunistic infections (OI) related to the immunosuppression. There are a large number of potential OI that might affect patients with IBD. The true prevalence of these infections is unknown, and can vary from country to country. Therefore, reactivation or de novo acquisition of infections such as tuberculosis, malaria, and viral hepatitis will be much more frequent in endemic areas. Therefore, physicians should be aware of these aspects when planning specific preventive measures for patients traveling to a particular country. This includes good control of environmental exposure, chemoprophylaxis when indicated, and the use of a specific vaccination program to prevent endemic infections. In addition, it should be noted that, though the risk of acquiring an infectious disease is probably greater for IBD patients traveling from a developed to a developing country, the inverse situation can also occur; it depends on the previous acquired immunity of the host against infections in any particular environment.

Time series analysis of Japanese encephalitis and weather in Linyi City, China

OBJECTIVES

To examine the relationship between meteorological factors and epidemiological pattern of Japanese encephalitis in Linyi City during 1956-2004.

METHODS

Autoregressive integrated moving average (ARIMA) models were used to evaluate the relationship between monthly JE incidence and weather factors. Logarithmic transformation was applied to the JE incidence series to assure the normality and homogeneity of variance of the residuals. The effect of mass vaccination on JE incidence was also evaluated using a transfer function in the time series analysis.

RESULTS

The analysis suggested that monthly average temperature [β = 0.0574, 95% confidence interval (CI) = (0.0172, 0.0976)] and relative humidity [β = 0.0082, 95% CI = (0.0004, 0.0158)] were positively associated with the logarithmic incidence of Japanese encephalitis after adjusting for mass vaccination in this area.

CONCLUSIONS

Weather variables might be treated as possible predictors of Japanese encephalitis incidence for regions with similar geographic, weather, and socio-economic conditions to Linyi, China.