Japan may face a shortage of influenza vaccines this winter due to a production delay.

The supply volume is currently projected at some 25.28 million units, equivalent to 50.56 million doses, about 1.14 million units lower than the estimated amount used during the previous flu season and the second-lowest level in 10 years.

The delay in vaccine production came as the National Institute of Infectious Diseases replaced one of the four vaccine strains it selected for this winter, due to slow propagation.

“We ask those aged 13 and over to take only one dose of vaccine this winter, instead of two,” a health ministry official said.

Each season, the NIID selects vaccine strains based on its flu projection, and vaccines are created by drug makers using chicken eggs.

According to the ministry, about 27.84 million units of vaccine were manufactured for last season, and some 26.42 million units of the total are estimated to have been used.

For this season, the propagation of one of the four NIID-selected vaccine strains was poorer than expected, leading to an estimate that production of that strain will fall by about 30 percent or more from last season’s level. NIID replaced this strain with a new one, and the change led to the delayed production.

With Japan’s influenza outbreak usually peaking in January-February, people are advised to be vaccinated by mid-December.

This season, however, vaccine supply is projected to peak in the third week of December, later than usual.

The ministry has asked medical institutions and drug wholesalers to make sure that vaccine stocks are managed appropriately.

“If each person gets only one dose, the total number of vaccinated people would almost reach last season’s level,” the ministry official said.