Available Vaccines
Hepatitis A
Introduction
Hepatitis A is an acute liver infection caused by the hepatitis A virus (HAV), a member of the Hepatovirus genus with the Picornaviridae family. The virus has only one serotype with a single-stranded RNA genome.
The virus spreads primarily via the fecal–oral route, through ingestion of contaminated food and water, or direct contact with an infectious person. While most infections in young children are asymptomatic, older individuals commonly experience symptomatic disease that include jaundice and hepatitis. There is no chronic stage, but occasional fulminant cases may occur in 1-2% of those aged over 49 years. Ultimately, hepatitis A resolves completely in >99% of cases. However symptomatic relapse has been reported in 3-20% of clinical cases.
The disease occurs worldwide, with both minor and major outbreaks. Many cases go unreported due to the high proportion of subclinical infections. In Malaysia, hepatitis A has declined significantly with reported cases having dropped to 0.19/100,000 in 2022. This reduced population immunity increases the risk of outbreaks in a largely susceptible community, similar to trends seen in other high-income countries.
Table 10.1 Vaccines Registered in Malaysia
Table 10.2 High-Risk Groups in Malaysia
Implications for Healthcare Workers
Outbreaks of hepatitis A among hospital staff occur occasionally, usually in association with an unsuspected index patient who is fecally incontinent. In most outbreaks, nurses accounted for most of the personnel infected.
Evidence for Safety and Effectiveness
Hepatitis A vaccines are highly effective in adults, with 94–100% developing protective antibodies within a month after the first dose and all achieving protection after the second dose. Clinical experience suggests that protection following vaccination may be present even if anti-HAV antibodies are not detectable. A positive (qualitative) test for total anti-HAV antibodies is considered to signify immunity against HAV infection.
In large prelicensure safety studies of 2 different inactivated hepatitis A vaccines in adult recipients, local reactions, including soreness or tenderness at injection site, were reported in 56% and 53% respectively for the 2 vaccines. Headache was reported in 14–16% of adults for both vaccines.
In adults, persistence of the vaccine-induced immune response following primary 2-dose vaccination with inactivated hepatitis A has been shown to persist for up to 15 years. Evidence has now been obtained to suggest that immunization against HAV with a killed vaccine also leads to a measurable cellular protective immune response, which is long-lasting for at least 6 years and may be boosted to revive the immune memory.
References
- Malaysian National Centre of Adverse Drug Reactions Database. (2019). [Database]. Accessed 10 October 2019.
- Ministry of Health Malaysia (2023, October) Malaysia health facts 2022. https://www.moh.gov.my/moh/resources/Penerbitan/Penerbitan%20Utama/4._Health_Facts_2023-compressed_.pdf
- World Health Organization (October 7, 2022). WHO position paper on hepatitis A vaccines Weekly epidemiological record;40(97):493-512. https://www.who.int/publications/i/item/who-wer9740-493-512
- National Pharmaceutical Regulatory Agency (NPRA). Sistem Pendaftaran Produk & Perlesenan. https://quest3plus.bpfk.gov.my/pmo2/index.php
- World Health Organization. (Update 2019). Immunological Basis for Immunization Series: Module 18 – Hepatitis A. https://www.who.int/publications/i/item/97892516327
- Centers for Disease Control and Prevention. (2021). Epidemiology and prevention of vaccine-preventable diseases (14th ed.; Hall, E., Wodi, A. P., Hamborsky, J., et al., Eds.). Public Health Foundation. https://www.merle-arbeitsmedizin.de/wp-content/uploads/2022/02/CDC-Pink-Book-Version-14th-Edition.pdf