Resurgence of human metapneumovirus infection and influenza after three seasons of inactivity in the post‐COVID‐19 era in Hokkaido, Japan, 2022–2023

Abstract

Following the coronavirus disease 2019 (COVID‐19) outbreak in February 2020, incidences of various infectious diseases decreased notably in Hokkaido Prefecture, Japan. However, Japan began gradually easing COVID‐19 infection control measures in 2022. Here, we conducted a survey of children hospitalized with human metapneumovirus (hMPV), influenza A and B, and respiratory syncytial virus infections in 18 hospitals across Hokkaido Prefecture, Japan, spanning from July 2019 to June 2023. From March 2020 to June 2022 (28 months), only 13 patients were hospitalized with hMPV, and two patients had influenza A. However, in October to November 2022, there was a re‐emergence of hMPV infections, with a maximum of 27 hospitalizations per week. From July 2022 to June 2023 (12 months), the number of hMPV‐related hospitalizations dramatically increased to 317 patients, with the majority aged 3–6 years (38.2%, [121/317]). Influenza A also showed an increase from December 2022, with a peak of 13 hospitalizations per week in March 2023, considerably fewer than the pre‐COVID‐19 outbreak in December 2019, when rates reached 45 hospitalizations per week. These findings suggest the possibility of observing more resurgences in infectious diseases in Japan after 2023 if infection control measures continue to be relaxed. Caution is needed in managing potential outbreaks.

A significant outbreak of respiratory human adenovirus infections among children aged 3−6 years in Hokkaido, Japan, in 2023

“…This shift echoes a similar trend observed during the resurgence of RSV and hMPV infections in our previous study in 2021 and 2022, where the predominant age group requiring hospitalization became older compared with the pre-COVID-19 era. 15,21 This pattern aligns with similar trends reported globally. 13,22,23 In Japan, public health institutes and public health centers nationwide detect HAdV based on the manuals provided by the National Institute of Infectious Diseases (NIID), Japan, with their data integrated by the NIID.…”

“…In Hokkaido Prefecture, hMPV infections and influenza, which had been scarcely observed since March 2020, experienced resurgences around October 2022 and March 2023, respectively. 15 At the end of 2023, Hokkaido Prefecture faced a significant resurgence of respiratory HAdV infections, unlike anything observed in recent years. Since July 2019, we have been conducting surveillance of pediatric hospitalizations due to infectious diseases across multiple facilities in Hokkaido Prefecture.…”