The embassy in the Cuban capital has been operating under ordered departure status since Sept. 29, 2017, due to the reported health attacks affecting its employees.
The State Department said in a statement that on March 5, a new permanent staffing plan will take effect.
"The embassy will continue to operate with the minimum personnel necessary to perform core diplomatic and consular functions, similar to the level of emergency staffing maintained during ordered departure," it said.
The State Department added that the embassy will operate as an unaccompanied post, defined as a post at which no family members are permitted to reside.
However, the State Department admitted that it still did "not have definitive answers on the source or cause of the attacks, and an investigation into the attacks is ongoing."
It said that the health and safety of US government personnel and family members "were a key factor in the decision to reduce the number of personnel assigned to Havana."
The United States has not formally accused Cuba of carrying out the attacks, yet it highlighted the unexplained physical afflictions suffered by 24 US embassy personnel in Cuba, leading to the partial closure of the embassy and suspension of granting visas to the Cubans.
For its part, Cuba denied the accusations, saying the investigation to resolve the matter was still in progress and that "effective cooperation" of the US authorities was essential.