The State Department announced Friday it will permanently maintain a skeletal staff at the U.S. embassy in Cuba citing the “health attacks” on its personnel that have baffled experts to this day.

The decision to maintain the staff at 40 per cent will have a sweeping impact across U.S. intelligence, small business owners, Cuban migration, and human rights advocates. The reaction by many who support engagement with Cuba has been swift.

James Williams, President of Engage Cuba, a group that advocates for engagement with the island, laments the decision, particularly because Cuba will soon go through one of the biggest political transitions in recent history when Raul Castro steps down on April 19.

“While Cuba is going through the most historic transition in almost 60 years, the United States is going to be blind on the island,” Williams said.

The decision is “not going to help with human rights, political reform, economic reform, not to mention Cuban families being connected as a result,” he said.

Last October, the State Department ordered non-essential embassy personnel and the families of all staff to leave Havana, arguing the U.S. could not protect them from unexplained illnesses that have harmed at least 24 Americans. But by law, the department can only order diplomats to leave for six months before either sending them back or making the reductions permanent.

The six months expire Sunday. So the department said it was setting in place a new, permanent staffing plan that maintains a lower level of roughly two-dozen people — "the minimum personnel necessary to perform core diplomatic and consular functions." The department also said that the embassy in Havana would operate as an "unaccompanied post," meaning diplomats posted there will not be allowed to have spouses or children live with them in the country.

The Morning Rundown Get a head start on the morning's top stories. This site is protected by recaptcha

Camilo Condis, an entrepreneur in Havana, says he is concerned about the impact this will have on those in the private sector. It comes at a crucial time, when many are anticipating an announcement by the Cuban government to curtail private businesses.

Condis, who rents an apartment to locals and is a senior manager at Artecorte, a non-profit that holds community activities, said “many of us will lose the opportunity to visit our families in the U.S.” Because of the scarcity of supplies on the island “many entrepreneurs buy many or most of the items they need for their businesses in the U.S.”

Martha Honey, the executive director of the Center for Responsible Travel, a non-profit focused on sustainable tourism, said how this will affect U.S. travel to Cuba is still a question mark, though she is cautiously optimistic.

She said the State Department’s position has been that when there is a draw down of diplomats at an embassy, they have to simultaneously issue a travel warning and caution the public that the embassy has been downsized.

“It sets a new normal. And the new normal is that the current size of the embassy staff will remain. My reading is that this could change the status of the travel warning against Cuba from a level three to a level two,” Honey said.

When the U.S. ordered its personnel out of Cuba, it had issued a warning advising Americans not to travel to the country. In January, when the State Department changed its travel alert system, it changed the warning to a level 3 and recommended Americans “reconsider” traveling to Cuba.

The downsizing of the embassy staff along with a travel warning have had significant effects on Cuba's economy and for its citizens. With fewer employees on hand, the U.S. Embassy in Havana halted visa processing, forcing Cubans who wish to visit the United States to seek visas through U.S. embassies in other countries. The U.S. is also expected to fall far short of granting the 20,000 immigrant visas to Cubans that have been allotted annually for decades.

Secretary of State Rex Tillerson signed off on the permanent plan for reduced staffing out of concern for "the health, safety and well-being of U.S. government personnel and family members," the department said in a statement.

"We still do not have definitive answers on the source or cause of the attacks, and an investigation into the attacks is ongoing," the department said.

Cuba has repeatedly denied either involvement in or knowledge of any attacks, and has said its own investigation into the illnesses has turned up no evidence of deliberate action. The United States has not accused Cuba of such action but has said Havana holds responsibility nonetheless, arguing that such incidents could not have occurred on the small, communist-run island without the knowledge of Cuban officials.

The mysterious case has sent U.S.-Cuba relations plummeting from what had been a high point when the two countries, estranged for a half-century, restored full diplomatic ties under President Barack Obama in 2015.

In late 2016, U.S. Embassy personnel began seeking medical care for hearing loss and ear-ringing that they linked to weird noises or vibrations — initially leading investigators to suspect "sonic attacks."

An interim FBI report disclosed by The Associated Press in early January said the investigation has uncovered no evidence that sound waves could have damaged the Americans' health. But Tillerson has said he's still convinced the diplomats were hit by deliberate, specific attacks targeting their health.

Doctors treating the patients said in a study published last month that the sounds heard by diplomats might have been a byproduct of something else that might help explain the full symptom list: memory problems, impaired concentration, irritability, balance problems and dizziness. The study in the Journal of the American Medical Association said doctors still have no clear diagnosis of just what happened to trigger the mysterious health problems.

The Associated Press contributed to this report.

FOLLOW NBC LATINO ON FACEBOOK, TWITTER AND INSTAGRAM