Diseases and vaccines

Japanese encephalitis vaccine

• SA 14-14-2 vaccine
• Mouse-brain derived vaccine
• Other JE vaccines

Live, attenuated SA 14-14-2 vaccine

Fortunately, an additional option for Japanese encephalitis (JE) vaccination has recently become internationally available. The live, attenuated SA 14-14-2 vaccine was developed in China and has been used there since 1988. Outside China, it has been licensed and used in South Korea and Nepal, licensed in Sri Lanka and, most recently, it was licensed and introduced in India in 2006. The vaccine is very effective and inexpensive. More than 200 million doses have been given without any recorded severe side effects. It also appears feasible that a single dose of vaccine will provide life-long protection.

The next step in making this vaccine more widely available will be prequalification of the vaccine by the World Health Organization. It is exciting that this vaccine, developed and produced in Asia, may provide the solution for expanding JE vaccination to protect all the children of Asia.

Inactivated, mouse brain-derived vaccine

Until recently, the most widely used and available JE vaccine has been a mouse brain-derived, inactivated vaccine. It has been produced by several countries, including Japan, South Korea, Thailand, India, and Vietnam and has been used in many more. However, there are reasons the mouse brain-derived vaccine is not the answer to JE vaccine needs in Asia:

• It is expensive.
• It has a complicated dosing schedule.
• Since the early 1990s, there have been concerns about side effects from this vaccine.
• The limited supply of the vaccine has never been enough for global needs, and now the major manufacturers of this vaccine have stopped production in anticipation of improved vaccines becoming available (see below).

Other JE vaccines

Several other JE vaccines are in development, but there will be a longer timeline until they are widely available, particularly for children. These vaccines include a live, attenuated “chimeric” vaccine that uses a yellow fever vaccine virus strain as its backbone (ChimeriVax-JE, manufactured by Acambis). It is currently undergoing clinical trials in adults to test its safety and immunogenicity.

Clinical trials also are underway for a JE vaccine candidate manufactured by Intercell. Following a successful Phase II study in the United States, Intercell initiated Phase III trials in September 2005 to test the vaccine’s safety and immunogenicity in nearly 5,000 adult subjects throughout the United States, Europe, and other countries. This vaccine is inactivated but does not require mouse brains for production.