About 80 percent of COVID-19 patients from the virus-hit Diamond Princess cruise ship showed mild symptoms or none at all, according to a report compiled by the Self-Defense Forces Central Hospital.

The Tokyo hospital accepted patients who tested positive for the virus in polymerase chain reaction (PCR) checks on the ship, and gave an analysis of 104 people who agreed to cooperate for the report and its release.

The report is believed to be one of the largest analyses of symptoms caused by the new virus to be compiled in Japan, according to the Defense Ministry, and was posted on the hospital’s website for medical workers.

The proportions of patients who showed no symptoms when hospitalized was 40 percent, as was the proportion who showed mild symptoms, while the remaining 20 percent showed serious symptoms, according to the report.

But it added that computed tomography (CT) scans of the lungs of patients with no or mild symptoms showed that half of them still had abnormalities apparently caused by the virus.

The most common symptom seen when the patients were hospitalized was a fever, followed by coughing.

The average age of the patients was 68. Among them, 48 percent had underlying diseases, with the largest proportion of them experiencing high blood pressure.