TOKYO -- The number of measles cases is rising across Japan, but many on social media are spreading misinformation that the disease is not serious. Ahead of the World Expo opening April 13 in Osaka, the Mainichi Shimbun checked the facts.

In the middle of March, a post on the X social media platform viewed over 1 million times within two days described measles as a common illness that everyone used to catch in their childhood and that the symptoms were less severe if contracted at that time.

A "community note" was posted in response, as they often are on the platform to correct faulty claims, and a number of users chimed in about the risks carried by the disease. However, many also agreed with the post, saying things like, "In the past, the disease was so ubiquitous that children would go out to play with infected friends to pass it on," and "Japanese people have become weak."

Takashi Nakano, a specially-appointed professor in pediatrics at Kawasaki Medical School and an expert on infectious diseases, said, "Measles has always been a life-threatening disease."

Measles is among the most infectious agents of all pathogens. It frequently causes complications, with pneumonia and encephalitis killing 1 in 1,000 patients. Subacute sclerosing panencephalitis (SSPE), also known as Dawson disease, is a progressive neurological disease that may develop after years of infection with the measles virus.

In response to the assertion that measles is a serious disease, some point to the low number of patients or how it is put in the same category as the seasonal flu.

According to Japan's National Institute of Infectious Diseases, as of March 19, 32 people have been infected with measles this year. This is above the pace of the previous year, while the number of cases remained 10 or less in the period from 2020 to 2022 during the coronavirus pandemic and below 50 in the following two years.

Nakano acknowledges the number used to be higher. In 2008, when full-scale surveys began, there were over 10,000 patients. Afterward, the national government implemented comprehensive countermeasures.

Vaccination rates were increased through regular shots and other means, and epidemiological surveys were conducted if even one patient appeared. The number of infections drastically declined, and in 2015, the World Health Organization (WHO) designated the disease as "eliminated" in Japan.

However, Nakano warned, "if the vaccination rate drops, the virus could become established in Japan again and the certification of elimination could be revoked."

This March, the WHO stated that the disease infected more people in Europe and Central Asia in 2024 than any time since 1997, cautioning that the risk of a global pandemic is rising.

Differences in vaccine effectiveness

Regarding the notion that measles is a minor disease if caught early, Nakano said, "It's true that once caught, one acquires strong immunity," adding, "However, a lot of children caught the disease in the era when few were vaccinated, and each year some nearly 100 kids died. For a disease like that, the best thing is to keep it from spreading."

Since the coronavirus pandemic, some remain staunchly opposed to or distrustful of vaccines in general. According to Nakano, there is a difference between the effectiveness of vaccines in preventing the onset of measles and respiratory illnesses, such as COVID and the flu. In contrast to the roughly two-day incubation period for the flu, the one for measles is around 11 days. Symptoms appear after viruses multiply in respiratory mucous membranes and circulate through the body in a process called viremia.

The immunity brought about by vaccines for diseases with long incubation periods is said to be strong. There is no cure for measles, only symptomatic treatments, which is why prevention is so important.

Nakano concluded, "Japan has reduced the number of people infected to near zero through high vaccination rates. Instead of being influenced by social trends, how about considering that there are people around you who are immunocompromised by illness and children who are not yet vaccinated?"

(Japanese original by Atsuko Ota, Digital News Group)