A cold virus called the respiratory syncytial virus (RSV) that causes inflammation of the respiratory tract in infants, which remained dormant last year, could soon see an unusual uptick in Japan.

RSV mainly spreads via respiratory droplets when a person coughs or sneezes, as well as through direct contact with a contaminated surface — somewhat similar transmission routes to the coronavirus. Unlike that virus, however, there are no vaccines available against RSV.

RSV usually causes cold-like symptoms, including fever and a severe cough, and most people recover in a week or two, but it can lead to more serious complications, especially for infants, older adults and those with immunodeficiency or congenital heart disease.

The virus typically spreads during fall, winter and spring. But according to the National Institute of Infectious Diseases, confirmed RSV infections have begun to emerge outside the peak period. The coronavirus outbreak last year somehow kept RSV at bay, but it has now begun to reemerge just as national COVID-19 cases remain relatively flat.

On Tuesday, the NIID said the number of RSV patients per medical institution was 3.87 in the week ending June 27 — the highest number of cases since 2019. In 2018, the year the counting system was changed, the infection count peaked in September at 2.46, and it reached 3.45 patients per medical institution a year later.

According to the institute, the number of patients per medical institution has been on the rise since mid-May, based on figures reported by about 3,000 pediatric departments nationwide. The highest number of cases by prefecture stood at 12.96 in Fukui, followed by 11.88 in Mie and 10.98 in Yamaguchi.

Following this spike in infections, virologists and health care providers are on alert over the virus and a possible increase in the number of patients in need of acute care.

But as worries over RSV intensify, concerns about COVID-19's impact on the health system are beginning to ease.

A COVID-19 intensive care unit in Kanagawa Prefecture | AFP-JIJI
A COVID-19 intensive care unit in Kanagawa Prefecture | AFP-JIJI

According to a recent report released by the NIID, the number of coronavirus infections and hospitalized patients has dropped, while the number critically ill from COVID-19 — including patients who require a treatment known as extracorporeal membrane oxygenation that uses artificial heart-lung devices — fell before leveling off. In severe RSV infections, oxygen administration may also be required.

Coronavirus figures were on a continuous upward trend from March 2021 until June 18 nationwide. Even though the number of positive COVID-19 test results has decreased in recent months, the number of critically ill patients, which had begun to drop earlier in June, has remained high since around June 17, the NIID said.

Concerns over RSV have already emerged in other parts of the world including in the U.S., which has seen a recent spike in infections, prompting the nation’s Centers for Disease Control and Prevention to warn of an unusual wave of the disease.

RSV is the most common cause of bronchiolitis and pneumonia in children under the age of 1 in the United States. According to the CDC, each year RSV leads to an average 58,000 hospitalizations and 100 to 500 deaths among children younger than 5 years old, as well as 177,000 hospitalizations and 14,000 deaths among adults age 65 years or older.

Experts say it is important to continue using preventive measures already familiar from the fight against the coronavirus, including proper hand hygiene and appropriate ventilation, to prevent RSV infections.

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