Over 100 people were struck by the H-1 type measles in February and March this year. It is a rare strain of the disease that broke out in Hong Kong some three years ago.

Compounding fears about the strain, a large swathe of those afflicted this year had been immunized against the measles, but the vaccination's effects had weakened over time.

"A new type of (measles) virus arose just as the immunity (provided by vaccination) was weakening, causing the large-scale outbreak," a center spokesman said. "People should actively pursue vaccination and be prepared to be vaccinated again following a certain period of time."

Ibaraki Prefectural Government officials said that the new strain of measles was detected in 109 people aged from a few months to 62. The large majority of those afflicted, 78, were junior high school pupils. Of 86 pupils, a number that includes those only suspected of having contracted the disease, 61 had been vaccinated for the measles.

Center officials said that Japan is usually afflicted by two types of measles, the D3 strain and D5 strain. However, they learned the strain that broke out in Kitaibaraki was of type H1.

Measles vaccinations are usually performed somewhere between 12 and 90 months of birth. However, center officials said that only about 80 percent of people undergo measles vaccination.

Recently, vaccinations have also developed a tendency to weaken in effect over time. Much debate over health issues has been devoted to repeat immunization.

Some pupils affected by the outbreak of the new measles virus had been vaccinated, but their symptoms were not as harsh as those who had not been immunized.

Measles causes fever and rashes to break out, with severe cases leading to encephalitis or pneumonia. The effects can often be greater if contracted by an adult.

Ministry of Health, Labor and Welfare statistics show that of the 35,302 reported cases of measles in Japan last year, those over 18 accounted for 925 instances. Of the 21 people who died through the measles in 2001, 10 were 18 or over. (Mainichi Shimbun, Oct. 28, 2002)