ROME — Around 300 children in Bologna, Italy, were not eligible to attend kindergarten this week because a temporary measure relaxing vaccination requirements expired and a previous, stricter law returned to force.

Dozens of other children across Italy were also likely to be affected, said Mario Rusconi, president of the Association of Head Teachers and Senior Staff in Lazio, Rome’s region.

A 2017 law made 10 vaccines obligatory for children who enrolled in Italian schools, a response to a worrisome decline in vaccinations nationwide and a measles outbreak that same year.

But last year, the Health Ministry, headed by a member of the Five Star Movement, one of the parties in the coalition government, adopted a temporary measure to allow children to stay in school as long as their parents attested they had been vaccinated. A doctor’s note was not needed.