A new development: Hepatitis A vaccine

In 1979, hepatitis A virus (HAV) was successfully grown in marmosets (small South American primates) and propagated in other cell cultures, thus enabling the beginning of vaccine development. An inactivated vaccine against HAV (HAVRIX) manufactured by SmithKline Beecham has been licensed in several European, Asian and African countries. Recently, it has been approved by the Food and Drug Administration (FDA) of the United States of America. Another inactivated HAV vaccine, produced by Merck Sharp and Dohme, is expected to be commercially available in the near future. Live attenuated hepatitis A vaccines (LAHAV) are still under development; two are now licensed in China. LAHAV are expected to be superior to inactivated HAV vaccines because with a smaller dose, they confer more durable protection without the need for injection

According to information provided by the manufacturer, HAVRIX contains inactivated HAV absorbed onto the surface of aluminum particles and suspended in a sterile solution. The vaccine is given intramuscularly in the deltoid. By 15 days post vaccination, 80-98% of adults develop specific antibodies against HAV, rising to 96% after one month. A booster dose is to be administered 6 to 12 months after the initial injection to prolong protection. The vaccine was shown to be safe and effective in extensive worldwide clinical trials. To-date, these vaccines have been protective for at least three years, and extrapolation models suggest that the vaccine should be protective for a minimum of 10 years.

The vaccine is well tolerated. It does not cause any symptoms of the hepatitis or a significant increase in serum liver enzyme concentration. The most common adverse effects noted in clinical trials were injection-site soreness that may last for 1 or 2 days and headache. Rare adverse effects, not observed in clinical trials conducted so far, may follow expanded commercial use of the vaccine. The vaccine is contraindicated in people with known hypersensitivity to any of its component.

The inactivated vaccine is recommended for people living in endemic areas, travelers to these areas, some military personnel, and certain high risk individuals such as some hospital and laboratory personnel, sewage workers and dietary personnel. Most hospital employees are not at risk and may not need to be vaccinated. Health workers dealing with very young children should be vaccinated against HAV if they were still susceptible to infection. Nosocomial outbreaks of HAV involving health care workers have been linked to HAV-infected infants with diarrhea in neonatal intensive care units.

Because the patterns of disease reflect standards of hygiene and sanitation, considerable variations exist in different populations. Seroprevalence studies indicate that more than 80% of people living in developing countries have evidence of HA infection by age of 20 years. Case-fatality rate due to hepatitis A (HA) is 3 to 7 per 1000. In regions with high endemicity, it would be ideal to administer HA vaccine within a program of infant and childhood vaccinations, possibly combined with the regular vaccination schedule. Whether HAV vaccine could be used for post-exposure prophylaxis or to control outbreaks remain unresolved issues.

HAV vaccine has not yet been added to the vaccination program of the Saudi Ministry of Health. However, some private health care providers may provide it in order to form a better decision on the benefits of using HAV in the general population in Saudi Arabia, we encourage all clinicians to report HA cases, to seek laboratory confirmation of hepatitis and report unspecified hepatitis if laboratory testing is not available.

The ultimate goal of HAV vaccine should be the complete interruption of transmission of HA. The epidemiology of HAV in humans, which is caused by one virus that infects only humans, suggests that eradication of the disease in the future is an achievable goal.

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