The Japanese government has approved a five-year grant, with ¥56 million slated for the first year, to create a single recombinant vaccine for four common childhood diseases. Researchers at Osaka University and Toyama Medical and Pharmaceutical University plan to insert genes encoding the antigens for measles, mumps and rubella into the varicella (chickenpox) virus. There are currently no recombinant vaccines against multiple diseases licensed for human use.

Improving vaccine coverage, particularly for measles, is a priority for Japanese health officials, says Keiko Taya, chief of the immunization program at Japan's Infectious Disease Surveillance Center. The government is currently assessing its vaccine policies—statistics indicate that measles coverage in 2001 was only 50% for one-year-olds, and that adult cases are on the rise.

According to project leader Koichi Yamanishi, the researchers decided to use varicella as the vector because it has a relatively large amount of dispensable DNA, which makes it a good candidate for accepting foreign genes. The team—which includes Michiaki Takahashi, who developed the Oka varicella vaccine now used worldwide—has already successfully expressed hepatitis B and HIV antigens in varicella.

Another advantage of varicella is that compared with other vaccines, such as measles, its side effects are relatively mild. “The varicella backbone is very safe,” says Anne Gershon, director of the pediatric infectious disease division at Columbia University. But Gershon cautions that the safety and efficacy testing process could take a long time—the researchers aim to have a vaccine ready for clinical trials within five years. Gershon also notes that current vaccines are safe and effective.

Yamanishi says Japan's problem may not be related to the effectiveness of the vaccines, but to the time it takes to receive them. Japanese children now receive four separate vaccinations for measles, mumps, rubella and varicella, a process prone to delays. Japan discontinued use of the MMR vaccine in 1993 over concerns that the Urabe mumps strain used in Japanese MMR vaccines was associated with adverse side effects such as meningitis. A new MMR vaccine isn't likely to be available for several more years. “If [a child] catches even a common cold during [that] year, the next injection gets delayed,” says Yamanishi. “One injection could be much more convenient.”