Increasing numbers of people with a fever have been visiting a Tokyo clinic amid a resurgence of coronavirus infections, and a significant number of them have already been vaccinated or infected before.

The clinic located in Suginami Ward says the number of outpatients has been rising since last week. It says the figure on Monday nearly doubled from a week ago, making it difficult to examine all the patients.

The clinic says that most of the people who tested positive had been vaccinated already. It says some people who had been infected during the sixth wave of COVID-19 were re-infected.

The clinic notes that some children have been infected with respiratory syncytial virus, or RSV, and human metapneumovirus rather than with coronavirus.

A 4-year-old girl who came to the clinic on Wednesday had RSV. But doctors say it is often difficult to distinguish these diseases by examining symptoms alone. The clinic conducts several tests for a diagnosis.

The clinic's director, Dr. Tamura Tsuyoshi, said the clinic had zero COVID patients on some days in June, but the number of infected people has been on rise since last week.

He said the infections are now mainly among people in their 20s and 30s but the wave could grow if infections spread among children and seniors. Tamura said he is worried that he may not be able to examine all the patients if that happens.

Tamura added that the virus appears to be highly infectious as even vaccinated people are testing positive.

He called on people with cold-like symptoms to stay home and rest to protect high-risk individuals. He also said it is important to follow basic anti-infection measures.