Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP)

This report updates the 1993 recommendations by CDC's Advisory Committee on Immunization Practices (ACIP) regarding the prevention of Japanese encephalitis (JE) among travelers (CDC. Inactivated Japanese encephalitis virus vaccine: recommendations of the Advisory Committee on Immunization Practices [ACIP]. MMWR 1993;42[No. RR-1]). This report summarizes the epidemiology of JE, describes the two JE vaccines that are licensed in the United States, and provides recommendations for their use among travelers and laboratory workers. JE virus (JEV), a mosquito-borne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Among an estimated 35,000-50,000 annual cases, 20%-30% of patients die, and 30%-50% of survivors have neurologic or psychiatric sequelae. No treatment exists. For most travelers to Asia, the risk for JE is very low but varies on the basis of destination, duration, season, and activities. JE vaccine is recommended for travelers who plan to spend a month or longer in endemic areas during the JEV transmission season and for laboratory workers with a potential for exposure to infectious JEV. JE vaccine should be considered for 1) short-term (<1 month) travelers to endemic areas during the JEV transmission season if they plan to travel outside of an urban area and will have an increased risk for JEV exposure; 2) travelers to an area with an ongoing JE outbreak; and 3) travelers to endemic areas who are uncertain of specific destinations, activities, or duration of travel. JE vaccine is not recommended for short-term travelers whose visit will be restricted to urban areas or times outside of a well-defined JEV transmission season. Two JE vaccines are licensed in the United States. An inactivated mouse brain--derived JE vaccine (JE-VAX [JE-MB]) has been licensed since 1992 to prevent JE in persons aged >or=1 year traveling to JE-endemic countries. Supplies of this vaccine are limited because production has ceased. In March 2009, an inactivated Vero cell culture-derived vaccine (IXIARO [JE-VC]) was licensed for use in persons aged >or=17 years. JE-MB is the only JE vaccine available for use in children aged 1-16 years, and remaining supplies will be reserved for use in this group.

Immunogenicity and safety of IXIARO (IC51) in a Phase II study in healthy Indian children between 1 and 3 years of age

For adults the standard administration of the Japanese encephalitis vaccine IXIARO is two injections of 6 microg in a 28-day interval. Immunogenicity and safety of 3 and 6 microg of IXIARO compared to JenceVac were investigated in 60 healthy Indian children aged between 1 and 3 years. JE specific neutralizing antibodies were measured at baseline and 28 days after the first and second vaccination. On Day 56 SCR of the 3 and 6 microg IXIARO and the JenceVac group were 95.7%, 95.2% and 90.9%, respectively, and GMT were 201, 218 and 230, respectively, both without statistically significant difference between the three groups. Local and systemic tolerability were captured in a diary 7 days post-vaccination. No apparent difference was seen in the safety profile between the vaccines. These first immunogenicity and safety data in children are promising and support the use of a 3 microg dose in children below the age of three for further development of IXIARO in the paediatric population.

[Study on safety and effect of purified inactivited Japanese encephalitis vaccine (primary hamster kidney cell, PHK)]

OBJECTIVE

In order to observe the safety and neutralizing antibody response to purified inactivated Japanese encephalitis vaccine (primary hamster kidney cell, PHK).

METHODS

Phase I, II, III field trials were performed and 943 healthy volunteers aged from 6 months to 10 years were administrated the JEV-I (PHK) vaccine at day 0 and day 7 respectively.

RESULTS

The vaccine did not cause any severe systemic and local adverse reactions. In phase I, 40 healthy volunteers were inoculated and the total reaction rate was 2.5%. In phase II and III, 903 healthy volunteers were inoculated JEV-I (PHK) and 101 healthy volunteers were inoculated with the Vero cell-derived JEV vaccine, the total adverse reaction rates were 6.2% and 14.2% respectively. The positive sero conversion rates of neutralizing antibody to the test and the control vaccine in antibody negative group were 96.9% (Geometric Mean Titers, GMT1:32.8) and 84.0% (GMT1:43.9) respectively and in antibody positive group were 93.1% (GMT1:167.2) and 100% (GMT1:181.0) respectively.

CONCLUSION

The JEV-I (PHK) vaccine is safe and effective. Trial Registration National Food drugs surveillance administrative bureau, "Medicine Clinical Experiment Written Directive from a Superior" number: 2003L00429.

IC-51, an injectable vaccine for the prevention of Japanese encephalitis virus infection

The mosquito-borne Japanese encephalitis (JE) virus is the major etiological agent of viral encephalitis in children living in South-East Asia, causing comas, seizures and Parkinson's disease-like movement disorders. Travelers and military personnel visiting the region are also highly susceptible to the disease. As the population in South-East Asia increases, more land is irrigated to produce rice paddies (the ideal breeding habitat for mosquitoes), and pig breeding (a zoonotic host for mosquitoes) becomes more widespread. Given the exponential growth in tourism to the region and the globalization of business and commerce, an enhanced requirement for mass vaccination exists. In the West, the current licensed vaccine against JE, JE-VAX, has been highly effective; however, the use of mouse brain-derived virus has been linked to cases of acute disseminated encephalomyelitis. Intercell AG, under license from VaccGen International LLC, is developing IC-51, a formalin-inactivated vaccine derived from cell culture-based attenuated virus that has been adapted to grow in Vero cells (African green monkey kidney cells). In extensive clinical trials performed to date, IC-51 was safe, with mild to moderate adverse events reported. In terms of immunogenicity, IC-51 was highly effective, demonstrating rapid seroconversion rates and long-term maintenance of geometric mean titers that exceeded the protective titer. The results suggests that IC-51 is fully compliant with the stringent regulatory requirements set by the WHO, has an acceptable safety profile and is non-inferior to JE-VAX.

Safety and immunogenicity of a Vero-cell-derived, inactivated Japanese encephalitis vaccine: a non-inferiority, phase III, randomised controlled trial

BACKGROUND

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in southeast Asia. Although no treatment is currently available, vaccination effectively prevents the disease. In a non-inferiority study, we aimed to compare the safety and immunogenicity of a novel, second-generation, inactivated candidate vaccine for JEV with a licensed, mouse-brain-derived vaccine.

METHODS

We included 867 adults in a multicentre, multinational, observer-blinded, randomised controlled phase III trial. Study sites were located in the USA, Germany, and Austria. Volunteers received either the JEV test vaccine intramuscularly on a two-dose schedule (on days 0 and 28; n=430) or the licensed vaccine subcutaneously according to its recommended three-dose schedule (on days 0, 7, and 28; n=437). The primary endpoint was immunogenicity, with respect to neutralising JEV-specific antibodies assessed by a plaque-reduction neutralisation test, which was assessable in 725 patients in the per-protocol population. This trial is registered as a clinical trial, EudraCT number 2004-002474-36.

FINDINGS

The safety profile of the test vaccine was good, and its local tolerability profile was more favourable than that of the licensed vaccine. Frequency of adverse events was similar between treatment groups, and vaccine-related adverse events were generally mild. The seroconversion rate of the test vaccine was 98% compared with 95% for the licensed vaccine on day 56 (95% CI for the difference -1.33 to 3.43). Geometric mean titre for recipients of the test vaccine was 244 (range 5-19 783), compared with 102 (5-1864) for the licensed vaccine (ratio 2.3 [95% CI 1.967-2.75]).

INTERPRETATION

The test JEV vaccine has a promising immunogenicity and safety profile.

Vaccines for preventing Japanese encephalitis

BACKGROUND

Vaccination is recognized as the only practical measure for preventing Japanese encephalitis. Production shortage, costs, and issues of licensure impair vaccination programmes in many affected countries. Concerns over vaccine effectiveness and safety also have a negative impact on acceptance and uptake.

OBJECTIVES

To evaluate vaccines for preventing Japanese encephalitis in terms of effectiveness, adverse events, and immunogenicity.

SEARCH STRATEGY

In March 2007, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library 2007, Issue 1), MEDLINE, EMBASE, LILACS, BIOSIS, and reference lists. We also attempted to contact corresponding authors and vaccine companies.

SELECTION CRITERIA

Randomized controlled trials (RCTs), including cluster-RCTs, comparing Japanese encephalitis vaccines with placebo (inert agent or unrelated vaccine), no intervention, or alternative Japanese encephalitis vaccine.

DATA COLLECTION AND ANALYSIS

Authors independently extracted data and assessed methodological quality. Dichotomous data were compared with relative risks and a 95% confidence interval (CI), and converted into percentage vaccine efficacy.

MAIN RESULTS

Eight RCTs involving 358,750 participants were included. These trials investigated two available and three pre-licensure vaccines. Two RCTs assessing efficacy of the commercially available inactivated Nakayama vaccine were identified. A two-dose schedule of the licensed vaccine provided significant protection of 95% (95% CI 10% to 100%) for one year only, while two doses of an unpurified precursor vaccine protected children by 81% (95% CI 45% to 94%) in year one and by 59% (95% CI 2% to 83%) in year two. Serious adverse events were not observed. Mild and moderate episodes of injection site soreness, fever, headache, and nausea were reported in less than 6% of children receiving inactivated vaccine compared to 0.6% of unvaccinated controls. One cluster-RCT compared the live-attenuated SA14-14-2 vaccine (widely used in China) with no intervention measuring adverse events. Fever was reported in 2.7% of vaccinees compared to 3.1% of controls, while 0.1% of both groups suffered diarrhoea or seizures. Four small pre-licensure RCTs assessing a genetically engineered vaccine and two cell culture-derived inactivated vaccines revealed high immunogenicity and relative safety.

AUTHORS' CONCLUSIONS

Only one of the three currently used vaccines has been assessed for efficacy in a RCT. Other RCTs have assessed their safety, however, and they appear to cause only occasional mild or moderate adverse events. Further trials of effectiveness and safety are needed for the currently used vaccines, especially concerning dose levels and schedules. Trials investigating several new vaccines are planned or in progress.

Comparative safety and efficacy of subcutaneous and intradermal administration of inactivated Japanese encephalitis vaccine during predeployment preparations in the Australian Defence Force

Japanese encephalitis is a viral disease emerging in areas of influence for the Australian Defence Force immediately north of the continent, including the Torres Strait border of Australia and Papua, New Guinea. Only the mouse brain-derived, inactivated, Nakayama strain vaccine is commercially available to the Australian Defence Force. This vaccine has a high cost and significant adverse event profile, requiring restricted duties after administration. To address these issues, intradermal vaccination (either single intradermal administration or two intradermal injections at two separate sites) was assessed, compared with the conventional subcutaneous vaccination method, in a randomized controlled trial among soldiers preparing for deployment. Dual intradermal vaccination (0.1 mL at two sites) was found to have a slightly more favorable adverse event profile while maintaining comparable serological efficacy and reduced cost. An expansion of the concept and a test of logistics were conducted by vaccinating a battalion formation during predeployment medical preparations. The method of vaccination was well accepted and retained comparable immunogenicity.

A Phase 2 study of a purified, inactivated virus vaccine to prevent Japanese encephalitis

Japanese encephalitis (JE) is a serious disease caused by the JE virus. New generation JE vaccines are needed to prevent this disease. We conducted this Phase 2 randomized, open label, unblinded, single center study of a new, cell-culture derived, purified inactivated virus (JE-PIV) vaccine. The JE-PIV vaccine was administered in either two or three intramuscular (IM) doses (6.0 or 12.0 mcg each) with observation over 8 weeks. All volunteers completed the protocol without serious adverse reactions. Headache and transient tenderness at the injection site were the most common complaints. There were no laboratory abnormalities believed to be related to vaccine during the study. JE-PIV was well tolerated, resulted in high seroconversion rates [Day 56 (primary endpoint); 95-100%] and induced enduring immune responses up to 2 years after vaccination. Expanded Phase 3 trials are planned.

West Nile virus infection and serologic response among persons previously vaccinated against yellow fever and Japanese encephalitis viruses

It is hypothesized that previous heterologous flaviviral exposure may modulate clinical illness among persons infected with West Nile virus (WNV). Little is known about the serological response in such persons. In summer 2003, a WNV outbreak occurred in Colorado, the location of the Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases (DVBID). DVBID employees, most previously vaccinated with yellow fever virus (YFV) or Japanese encephalitis virus (JEV) vaccines, were studied to determine whether previous vaccination affected symptom development among those subsequently infected with WNV during the outbreak, as well as their serological response. Serum samples collected in December 2003 and previously banked samples were tested using the plaque reduction neutralization test (PRNT) against WNV, Saint Louis encephalitis virus, dengue- 4 virus, JEV, and YFV. Specimens shown to have WNV antibody by PRNT were tested by IgM and IgG enzymelinked immunosorbent assays (ELISAs). Ten (9%) of 113 serosurvey participants had WNV neutralizing antibody titers in December 2003. PRNT titers from previous specimens showed that one of the ten had seroconverted to WNV before 2003. Of the remaining nine participants, seven reported illness in the summer of 2003, two of which were unvaccinated and five previously vaccinated. In the December 2003 specimens, five persons previously unvaccinated or vaccinated only against YFV had a fourfold or greater neutralizing titer with WNV than with other flaviviruses, whereas no persons previously vaccinated against JEV or JEV and YFV showed a similar difference in neutralizing titers. Eight of nine persons infected in 2003 had negative or indeterminate WNV MAC-ELISA results in the December 2003 sample; the ninth person was vaccinated against YFV one month previously, and was also YFV positive by MAC-ELISA. We conclude that previous flaviviral vaccination does not markedly affect the development of WNV fever and that the IgM antibody response in patients without neuroinvasive WNV disease is transient.

[Evaluation of mouse brain-derived, inactivated Japanese encephalitis vaccine]

Japanese encephalitis (JE) is a serious encephalitis caused by JE virus. Approximately 20% of JE patients die and 50% patients recover with neuro-psychiatric sequelae. In Japan, the number of JE patients was over 1000 per year in 1960s; however, the number decreased dramatically and has been less than 10 since 1990. Ministry of Health, Labour and Welfare suspended the strong recommendation for vaccination with the mouse brain-derived JE vaccine, because of cases who developed acute disseminated encephalomyelitis (ADEM) after vaccination with JE vaccine. However, it has not been fully confirmed on scientific bases that ADEM was caused by mouse brain-derived JE vaccine. Tissue culture derived-JE vaccine is under development. It is expected that this new vaccine will come to the market soon and that the recommendation of universal vaccination with JE vaccine will be implemented at the earliest occasion.

[Background of recent JE vaccine issues]

In Japan, more than 5,000 patients were reported in 1950, and there have been less than 10 cases annually since 1992. However, Japanese encephalitis virus caused of Japanese encephalitis (JE) are still existed highly and widely in the country, reported by National Institute of Infectious Diseases with serological examination among domestic pig population. JE immunization had been provided to children as category 1 routine immunization in Japan. However, the Ministry of Health, Labor and Welfare (HOHLW) decided not to recommend JE immunization to children as a routine immunization at May 2005. Major reason on this decision was that the Minter of MOHLW certified to pay loss of medical costs for the case of ADEM (acute disseminated encephalomyelopathy) after JE immunization, recognized as adverse events with JE vaccine, although MOHLW stated that the strict scientific evidence was unknown. MOHLW stated also that it is expected Vero cell derived JE vaccine should be replaced with the present mouse brain derived JE vaccine as the next generation, to be able to avoid theoretical possibility of neurological adverse events associated with JE vaccine. Small but increasing number of requests recently to be certified as health injuries on ADEM cases associated with JE immunization is also another reason for MOHLLW's decision. Further, fifth doses of JE vaccine given to children at 14-15 years old as a routine immunization was decided to be discontinued by MOHLW at July 2005, considering present epidemiological situation on JE and JE immunization status in Japan, although four doses has been recommended continuously as routine. The background details on JE vaccine issues decided by MOHLW in 2005 were reviewed on this paper.

[Flavivirus infections: yellow fever, dengue fever and Japanese encephalitis]

Flavivirus infections, such as dengue fever, yellow fever and Japanese encephalitis, are untreatable. As a result of the high prevalence of dengue fever in endemic areas, it poses a substantial risk for travellers to those areas. When it comes to Japanese encephalitis and yellow fever, the risk for travellers is limited but the diseases are extremely serious, creating a dilemma for the physician when it comes to deciding whether to vaccinate against them. The vaccines against both potentially have side effects. The indications and contraindications for vaccination are described in detail.

Report on a WHO consultation on immunological endpoints for evaluation of new Japanese encephalitis vaccines, WHO, Geneva, 2-3 September, 2004

The World Health Organization (WHO) is undertaking consultations on immunological responses as parameters for evaluation and licensure of new Japanese encephalitis (JE) vaccines. Immunological markers could be used by vaccine developers and regulatory authorities to assess vaccine efficacy in absence of clinical efficacy data. The consultation which is reported here reviewed current data on mechanisms of protective immunity gathered from animal experimentation, clinical data from licensed vaccines and from vaccine candidates still in clinical development. Immunological assays and readouts for use in evaluation of candidate vaccines were also discussed. The consultation made a series of recommendations for specifications on immunological criteria to assess JE vaccine efficacy. More detailed recommendations will be drafted following further consultations to serve as WHO guidelines for evaluation and licensure for new JE vaccines.

Yellow fever and Japanese encephalitis vaccines: indications and complications

Appropriate administration of yellow fever or Japanese encephalitis vaccines to travelers requires an assessment of the traveler's risk for infection with these vector-borne flaviviruses during their travels and the presence of risk factors for adverse events following immunization. Japanese encephalitis and yellow fever vaccines have been more frequently associated with serious adverse events following immunization since the early 1980s and the late 1990s, respectively. This article describes the adverse events, the magnitude of their risk, and associated risk factors.

Construction of recombinant pseudorabies virus expressing NS1 protein of Japanese encephalitis (SA14-14-2) virus and its safety and immunogenicity

The bivalent genetic engineering vaccine of Japanese encephalitis (JE) and Aujeszkj disease (AD) was developed to provide a novel approach to prevent and control these two diseases. NS1 gene of Japanese encephalitis virus (JEV) SA14-14-2 strain was produced by reverse transcriptase-mediated PCR (RT-PCR) and was cloned into vector pUSK to form recombinant plasmid (designed as pUSK-NS1). A co-transfection experiment was performed in porcine kidney (PK-15) cells with pUSK-NS1 and the genome of the vector virus (PRV TK(-)/gG(-)/LacZ(+) mutant). By plaque purification, PCR detection and southern hybridization, recombinant pseudorabies virus (PRV) expressing NS1 protein of JEV was acquired and named TK(-)/gG(-)/NS1(+). Western blot analysis and ELISA demonstrated the NS1 protein expression. To evaluate the recombinant virus's potential application, we characterized the safety and immune responses in Balb/c mice and swine. The safety test indicated that, when receiving the recombinant virus at a concentration of 10(6.0)pfu, no virulence of the recombinant virus to the mice, piglets and pregnant sows was observed. The vaccinated animals could acquire protective immunity against lethal challenge of the virulent PRV Ea strain and develop a good humoral and cellular immune response against JEV. The above results revealed that the recombinant virus could be a suitable candidate vaccine strain for developing a novel genetic vaccine to combat pseudorabies and Japanese encephalitis in the pig industry.