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Flu outbreak surging amid lower immunity, relaxed anti-COVID steps in Japan

The Central Government Building No. 5, which houses the Ministry of Health Labor and Welfare, is seen in Tokyo's Kasumigaseki district. (Mainichi/Kimi Takeuchi)

FUKUOKA -- The seasonal influenza has been spreading across Japan for the first time in three years, after strict COVID-19 countermeasures apparently helped keep flu infections at fairly low levels in 2021 and 2022.

    This winter, the number of flu patients has been on the rise primarily in western Japan, with some regions seeing the outbreaks reach alert levels, apparently due in part to the relaxation of anti-COVID-19 measures. Experts are warning that flu infections may further spread unlike normal years.

    The Ministry of Health, Labor and Welfare announced on Feb. 3 that the number of flu patients has reached warning levels across the country for the first time in three years. During the week up to Jan. 29, the number of patients per medical institution stood at 10.36, surpassing the warning level benchmark of 10 per institution.

    According to the ministry, the number of flu patients per medical institution nationwide had reached 1.24 during the week up to Dec. 25, 2022, above the criteria for an epidemic at 1 per establishment. Flu infections began to surge in January, with the number of patients jumping to 9.59 per institution over the week until Jan. 22.

    So what's behind the thriving flu infections?

    Hiroyuki Moriuchi, a Nagasaki University Hospital professor and pediatric infectious diseases specialist, speculated, "People have a weakened immune system as a result of having been unexposed to viruses amid intensified anti-coronavirus measures (in 2021 and 2022). And then multiple conditions for spreading infections have emerged, such as increased traffic between Japan and abroad and relaxed countermeasures against infections in the country."

    The concurrent spread of the coronavirus and influenza is dealing a serious blow to medical institutions.

    "It's difficult to tell whether a patient is infected with the coronavirus or flu based solely on their symptoms," said Michiko Kurokawa, director of the Kurokawa Michiko Pediatric Clinic in the city of Fukuoka.

    When feverish patients visit her clinic, staff first test them with kits that can detect both the coronavirus and flu, before examining them in different rooms depending on the test results. Over the past four days, about 20% of patients who tested positive had the coronavirus, while the remaining 80% had the flu.

    "For the first several hours after developing a fever, test results may not necessarily come back positive even if patients get tested. Even if they are negative, they need to be tested again if their symptoms continue," Kurokawa said, adding, "If patients develop a high fever, they become dehydrated, so they are advised to adequately take in water."

    Professor Moriuchi warned, "The flu can cause life-threatening complications such as encephalopathy. If patients have symptoms including convulsions, grogginess or uttering strange things, those around are advised to call emergency services immediately."

    While flu infections normally peak out in around early February, Moriuchi said, "The flu outbreak may continue due to deteriorating herd immunity and the changes in people's lifestyles. It is not too late to get vaccinated (against the flu) now."

    (Japanese original by Masanori Hirakawa, Kyushu News Department)

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