Five people in Japan suffered Guillain-Barre syndrome -- a disorder of progressive muscle weakness -- after receiving influenza vaccinations between January 2000 and April 2002, health ministry officials said Sunday.

The officials said the Health, Labor and Welfare Ministry ordered the pharmaceutical companies that make the vaccines to state clearly that the disease is a possible adverse effect of the products.

Guillain-Barre syndrome is named after the French physicians, Georges Guillain and Jean Barre, who first described it. The disease can cause immune system abnormalities, often inducing serious respiratory paralysis resulting from muscle weakness.

The annual incidence of the disease worldwide is about one or two per 100,000.

According to the ministry, three cases of the disease were reported in Japan in 1999, two in 2000 and two in 2001. Three were reported between December 2001 and April this year. Three of the recent victims have been children under the age of 10.

Before 1999, Japan had no reports of the disease developing following flu vaccinations, the ministry said.

There is no established theory for the cause of the disease, but many doctors assume it is brought on when the auto-antibody produced by a virus or bacteria infection damages the peripheral nerve system.

A report in the United States indicates the incidence of the disease goes up slightly after flu vaccinations.