According to the Japanese Ministry of Health, more than 150 cases of the fifth disease (erythema infectiosum) caused by parvovirus B19 are reported every week. Since the end of August 2024, more than 1’100 cases have been reported nationwide, a significant increase compared to the average incidence. Cases are reported especially in Kanagawa (> 160 cases), Saitama (> 250 cases) and Tokyo (> 260 cases) prefectures. The peak of the outbreak has not yet been reached.

An infection with parvovirus B19 is usually asymptomatic (up to 20%) to mild and self-limiting with cold-like symptoms, skin rash (“slapped cheek”) and arthralgia. High rates of virus circulation in the community pose a risk for pregnant women that have not been exposed to the virus previously and have developed protective immunity. Up to 10% of pregnant women infected with parvovirus B19 during the first 20 gestational weeks can experience complications such as hydrops fetalis and miscarriage. Other groups at risk of severe illness include individuals with blood disorders or weakened immune system.