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Malaysian Society of Infectious Diseases & Chemotherapy

Guidelines for Adult Immunisation

Content

Message from Editor

Editorial Panel

Adult Immunisation Schedule

Contraindications and Special Considerations

Temporary Deferral of Immunisation

Route and Site of Administration

Post Vaccination

Anaphylaxis

Vaccine Storage and Disposal of Vaccines

Vaccine Combinations

Multiple Vaccinations

Adverse Event Following Immunisation (AEFI)

Immunosenescence

Cholera

COVID-19

Dengue

Diphtheria

Tetanus

Pertussis

Haemophilus influenzae type b

Hepatitis A

Hepatitis B

Human Papillomavirus (HPV)

Influenza

Japanese Encephalitis (JE)

Measles

Mumps

Rubella

Meningococcal Disease

Mpox

Pneumococcal Disease

Poliomyelitis

Rabies

Respiratory Syncytial Virus (RSV)

Typhoid Fever

Chickenpox (Varicella)

Yellow Fever

Shingles (Zoster)

Passive Immunisation

Avian Influenza

Chikungunya

Clostridioides difficile

Ebola

Human Immunodeficiency Virus (HIV)

Malaria

Zika

Adults Who Missed Childhood Immunisation

Older Adults and Patients With Chronic Ilnesses

Healthcare workers

Human Immunodeficiency Virus (HIV)

Immunocompromised Patients

Miscellaneous Groups

Travelers

Vets & Animal Handlers

Abbreviations

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Available Vaccines

Japanese Encephalitis

In this chapter:

Introduction

Japanese encephalitis (JE) is an arbovirus central nervous system infection. Numerically, it is the most important cause of viral encephalitis across Asia. It has been estimated that 100,000 clinical cases of JE, with 25,000 deaths, occur around the world each year. The causative agent, Japanese encephalitis virus or JEV (family Flaviviridae, genus Flavivirus), is transmitted primarily among birds, pigs, and other vertebrate hosts by Culex species mosquitoes that breed in flooded rice fields and stagnant water and bite largely at dusk and night. While pigs and water birds serve as the primary amplifying hosts, humans are incidental dead-end hosts who become infected when they encroach on the enzootic cycle. The virus is found in Southeast Asia, India, Nepal, Pakistan, Sri Lanka, China, the Korean peninsula, Japan, Timor Leste, Pacific Rim islands and Australia.  In Malaysia, JEV exhibits an endemic transmission characterized by sporadic human cases throughout the year with seasonal peaks that coincide with high rainfall during the monsoon season.

In parts of Asia where JE is endemic, it is primarily a disease of children living in rural areas. Whilst most people living in endemic areas are infected by the age of 15 years, JE virus can infect all age groups, particularly when it is newly introduced into geographical areas where the general population has no pre-existing immunity. In addition, travelers from non-JE endemic regions are also at risk. In countries with longstanding childhood JE vaccination programs, such as Japan, South Korea, and Taiwan, the age distribution of cases has shifted toward adults, particularly to elderly people. Waning vaccine-induced immunity, immunosenescence in the elderly, and reduced natural boosting in urban populations may have contributed to increased incidence of JE among older individuals in endemic regions.

Only 1 in 300 infections result in symptomatic illness. These may range from a non-specific flu-like illness, febrile seizures, aseptic meningitis, encephalitis and poliomyelitis-like acute flaccid paralysis. There is no specific antiviral treatment for severe JE apart from supportive care. The acute case fatality rate of encephalitis is approximately 30%. Up to 50% of the survivors develop severe neurological sequelae such as seizures, limb weakness, hearing, visual and speech-language impairments, learning and psychobehavioural disabilities and Parkinsonian syndrome. Although the clinical condition of many JE survivors improves during the first 3–6 months after hospital discharge, less than 50% make a full recovery, and about 20% experienced subsequent deterioration on long-term follow-up.

In Malaysia, the great majority of laboratory-confirmed JE cases are found in Sarawak. There is a paucity of data on JE in other parts of Malaysia although two historical outbreaks have been documented in Pulau Langkawi in 1974 and Penang in 1988 and sporadic cases have been recorded in peninsular Malaysia and Sabah since 2000.

Table 14.1 Vaccines Registered in Malaysia

Table 14.2 High-risk Group in Malaysia

Implication for Healthcare Workers (HCWs)

There are no specific recommendations for JE vaccine for HCWs since they are generally not at special risk of contracting JE.

Evidence of Safety & Effectiveness

Undesirable effects and Safety
The safety profile of the live recombinant vaccine was comparable with that of other licensed vaccines (live attenuated JE, MMR, and hepatitis A).

Among adults, a significantly lower frequency of local adverse reactions was reported for live recombinant vaccine than mouse brain-derived vaccine. Otherwise, there was comparable tolerability and reactogenicity, with the majority of adverse events being mild to moderate and resolving within a few days. The most commonly reported adverse effects were headache (19%), myalgia (13%) fatigue (10%), influenza-like illness (9%), and nausea(5%).

Evidence of Effectiveness
Studies have shown the use of inactivated mouse brain derived and live attenuated vaccines have reduced considerably the incidence of JE in Sarawak. The average annual incidence of JE in Sarawak prior to the introduction of inactivated mouse brain-derived vaccine into the Expanded Programme of Immunisation (EPI) in 2001 was 9.8/100,000 aged 12 years and below. By the end of 2006, the average annual incidence had dropped to 4.3/100,000 aged 12 years and below. Malaysia has since switched to the use of the live-attenuated recombinant chimeric JE vaccine. At the end of 2022, a reduction of incidence rate to 0.07/100,000 with mortality rate of 0.01/100,000 was reported.

Since vaccination has no impact on the zoonotic transmission of the virus, susceptible individuals will continue to be at risk of disease even when few cases are observed. Thus, any vaccination programme would have to target all susceptible individuals without expecting herd immunity to contribute to a reduction in incidence.

References

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  2. Ministry of Health Malaysia (2023) Malaysia Health Facts 2022. Disease Control Division. https://www.moh.gov.my/moh/resources/Penerbitan/Penerbitan%20 Utama/4._Health_Facts_2023-compressed_.pdf

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  8. Ooi, M. H., Lewthwaite, P., Lai, B. F., Mohan, A., Clear, D., Lim, L., Krishnan, S., Preston, T., Chieng, C. H., Tio, P. H., Wong, S. C., Cardosa, J., & Solomon, T. (2008). The epidemiology, clinical features, and long-term prognosis of Japanese encephalitis in central Sarawak, Malaysia, 1997-2005. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 47(4), 458–468. https://doi. org/10.1086/590008

  9. World Health Organisation (2015). Japanese Encephalitis Vaccines: WHO position paper – February 2015. Weekly Epidemiological Record. 90(9):69-87. ] https://www. who.int/publications/i/item/japanese-encephalitis-vaccines-who-position-paper

  10. Monath, T. P., Guirakhoo, F., Nichols, R., Yoksan, S., Schrader, R., Murphy, C., Blum, P., Woodward, S., McCarthy, K., Mathis, D., Johnson, C., & Bedford, P. (2003). Chimeric live, attenuated vaccine against Japanese encephalitis (ChimeriVax-JE): phase 2 clinical trials for safety and immunogenicity, effect of vaccine dose and schedule, and memory response to challenge with inactivated Japanese encephalitis antigen. The Journal of infectious diseases, 188(8), 1213–1230. https://doi.org/10.1086/378356

  11. Torresi J, McCarthy K, Feroldi E, Méric C (November 23, 2010). Immunogenicity, safety and tolerability in adults of a new single-dose, live-attenuated vaccine against Japanese encephalitis: Randomised controlled phase 3 trials. Vaccine, 28(50):7993- 8000. doi: 10.1016/j.vaccine.2010.09.035.

  12. Wong, S. C., Ooi, M. H., Abdullah, A. R., Wong, S. Y., Krishnan, S., Tio, P. H., Pek, P. C., Lai, B. F., Mohan, A., Muhi, J., Kiyu, A., Arif, M. T., & Cardosa, M. J. (2008). A decade of Japanese encephalitis surveillance in Sarawak, Malaysia: 1997-2006. Tropical medicine & international health : TM & IH, 13(1), 52–55. https://doi.org/10.1111/j.1365- 3156.2007.01967.x

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