The Upper Perkiomen School District was forced to close schools Friday after 40 staff members called out sick — many citing side effects from coronavirus vaccinations this week, officials said.

On Wednesday afternoon and evening, 175 staff members and bus drivers were scheduled to get the Johnson & Johnson vaccine at the Montgomery County Intermediate Unit. Because of the expectation that some would experience side effects, the district already planned for Thursday to be a virtual day for its 3,200 students, and nearly 30 staff members ended up calling out sick.

But Superintendent Allyn Roche said he was “a little surprised” when that number climbed Thursday night. Some said they were waiting to see how they felt in the morning, and Roche asked principals to “get as creative with the schedules” as possible to offer in-person school Friday, given the complexities of social distancing in classrooms.

In the end, he said, “it was just too much,” and the district opted to close for the day.

A spokesperson for Montgomery County said the side effects were to be expected.

» READ MORE: COVID vaccine side effects: What if you don't have any?

“This is not a concern but what we are seeing with all COVID-19 vaccinations,” said Kelly Cofrancisco, noting that other schools had also planned virtual or asynchronous school days to prepare for increased callouts related to the teacher vaccination program.

» READ MORE: ‘Absolutely game-changing’: Teachers in the Philly suburbs have begun getting coronavirus vaccines

The Johnson & Johnson vaccine received emergency approval last month from the Food and Drug Administration and has produced mostly mild side effects. About half the people in clinical trials had a localized reaction to the vaccine — primarily pain at the injection site. And 55% experienced systemic side effects, including headache, fatigue, and muscle pain. Those reactions began on average two days after vaccination.

Over the past week and a half, Pennsylvania teachers have been receiving the one-dose vaccine through the regional Intermediate Units. Of the 94,600 doses the state has received and allotted for educators, nearly 84,000 have been administered, Gov. Tom Wolf said Friday.

Pennsylvania secured another 13,000 doses of the vaccine and will request another batch of that size next week, Wolf said. He said the state was ahead of its planned schedule for vaccinating teachers and expects to offer doses to every educator in Pennsylvania by the end of the month.

“That’s going to help students and teachers get back to schools, which we need them to do,” Wolf said during a news conference at the Bucks County Intermediate Unit.

» READ MORE: CDC drops school distancing guidelines from 6 feet to 3, paving the way for more kids to return to school

Staff writer Marie McCullough contributed to this article.