Japan's health ministry says it now appears difficult to reach its goal of giving rubella vaccine shots to 1.9 million men by the end of the fiscal year in March.
The ministry says only 38 percent of the target population had received shots as of the end of July. Officials say people may be trying to avoid hospital visits during the coronavirus pandemic.
Rubella, or German measles, is a viral infection that causes fevers, rashes and other symptoms. If pregnant women contract the disease, their babies are at risk of developing severe birth defects.
Following the 2018-2019 outbreak in Japan, the ministry started a vaccination campaign targeting men born between April 2, 1962, and April 1, 1979.
About 15 million men born during that period had no opportunity as children to receive the rubella vaccine through a government program.
The ministry hopes to raise the rate of men in this age bracket who have rubella antibodies to 90 percent or higher to help prevent another outbreak.
The ministry's vaccination drive began in June 2019. Vouchers for free antibody tests have been made available and those who test negative can get vaccinated at no cost.
The ministry aims to carry out antibody tests for about 9.2 million men. But as of July only 3.4 million had taken the tests, leading officials to say that this goal also appears unattainable.