HIROSHIMA PREFECTURE — Hiroshima University published a study in the journal PLOS One on May 8, 2026, detailing differences in long-term post-COVID symptom recovery patterns by infection variant and age group. The research followed 2,689 individuals diagnosed with COVID-19 between March 2020 and June 2024, including 1,524 adults and 1,165 children who completed surveys tracking 13 symptoms. Researchers compared recovery patterns across five pandemic periods: the original strain, Alpha, Delta, Omicron-2022, and Omicron-2024.

Aya Sugiyama, a lecturer at Hiroshima University's Graduate School of Biomedical and Health Sciences and lead author of the study, stated, "We found that the long-term course of post-COVID-19 symptoms varies significantly depending on the period of infection and age." At six months post-infection, an estimated 47% of adults infected during the Delta period reported lingering symptoms. The prevalence decreased to 23% during the Omicron wave in 2022 and 21% during Omicron infections in 2024. The study indicated that symptoms resolved more slowly in people infected during the Delta period compared to those infected during Omicron waves. Younger age was associated with quicker recovery, particularly in children aged 12 years and younger.

Sugiyama noted, "The prevalence among children remained about one-quarter to one-third that of adults throughout all epidemic waves." Two years after infection, approximately 20% of adults infected before the Omicron variant still reported symptoms, while 10% of adults infected during Omicron periods continued to report symptoms. The study found that symptoms persisting beyond two years showed little additional improvement over time. Persistent symptoms affected 4.1% of children infected during the Delta period and 1.9% of children infected during the Omicron-2022 period. Sugiyama added, "Notably, no children in the study experienced disruptions to daily life for more than two years after infection, even when symptoms persisted."

Why It Matters

The study provides data on varying recovery trajectories for post-COVID symptoms, detailing how different variants and age groups experience residual effects. The researchers plan to develop a model and a web-based tool to predict the risk and visualize the trajectory of persistent symptoms, aiming to enable earlier intervention and support.