BOSTON (AP) — The city of Boston has reached an agreement with the Boston Teachers Union over its COVID-19 vaccination policy, officials said Thursday.

The city will allow unvaccinated teachers to continue working if they submit proof of two negative COVID-19 screening tests per week during periods of lower virus transmission, Mayor Michelle Wu and the union said.

During periods of higher virus transmission, unvaccinated union members will not be allowed in school buildings, but may use accrued paid time off time as an alternative to being placed on unpaid administrative leave.

The agreement was approved Wednesday by about 84% of union members who voted.

The agreement “will ensure that all new hires must be vaccinated will help us prioritize a safe and healthy environment for students and staff,” Wu said in a statement.

The union, the city’s largest with about 10,000 members, said about 99% of members have already been vaccinated or received an exemption, while 367 union members have chosen to remain unvaccinated.

“The agreement takes important steps to promote public health and to mitigate classroom staffing disruptions,” the union said in a statement.

The agreement is subject to the approval of the Boston School Committee.

Wu also announced Thursday that the city will not lift its student and staff indoor mask mandate on Feb. 28 as allowed under new state guidance announced Wednesday. The city will wait until it sees “a consistent trend of downward progress” of coronavirus spread before making a decision on lifting school mask rules, she said.