As Japan marks the fifth anniversary of the confirmation of its first case of COVID-19 on Wednesday, people in the country are still being urged to exercise caution about the novel coronavirus disease.

Waves of infections have continued even after Japan lowered the classification of COVID-19 under the infectious disease law to Category V, the same as for seasonal influenza, in May 2023.

There have been reports of cases of prolonged COVID-19 aftereffects having an impact on patients' social lives.

Japan's first COVID-19 case was confirmed on Jan. 15, 2020, prompting the government to classify the disease as the second most severe category under the law.

At that time, the government required COVID-19 patients to be hospitalized and restricted their work, while collecting information on all patients.

After COVID-19 was downgraded to Category V, infection control measures were left to individual decisions.

According to the health ministry, more than 100,000 COVID-19 patients died in the country between 2020 and 2023.

Although there has been no major outbreak of a new coronavirus strain following the spread of the omicron variant since the downgrade, infections have repeatedly resurfaced in the summer and winter.

Basic infection control measures, such as washing hands and wearing masks, are important after free vaccination programs and public funding for COVID-19 treatment drugs ended at the end of March 2024.

Meanwhile, many former COVID-19 patients are still suffering from aftereffects such as malaise and headaches.

A research group at Okayama University analyzed roughly 740 patients who visited the outpatient clinic of the university's hospital that specializes in treating aftereffects between February 2021 and July 2023.

About 60 of them were diagnosed with myalgic encephalomyelitis, also known as chronic fatigue syndrome, in which unexplained fatigue makes daily life difficult.

The group said that the severity of symptoms after infection, vaccination status and smoking and drinking habits could cause differences in COVID-19 aftereffects.

The number of patients complaining of brain fog, in which patients have difficulty thinking clearly and concentrating, has been increasing since the emergence of the omicron variant.

"It is important to pay attention to fatigue and memory deterioration even after recovery and to receive appropriate evaluation and treatment," said Fumio Otsuka, professor at the university hospital.