WASHINGTON — The C.I.A. has found that most cases of the mysterious ailments known as Havana syndrome are unlikely to have been caused by Russia or another foreign adversary, agency officials said, a conclusion that angered victims.
A majority of the 1,000 cases reported to the government can be explained by environmental causes, undiagnosed medical conditions or stress, rather than a sustained global campaign by a foreign power, C.I.A. officials said, describing the interim findings of a comprehensive study.
The C.I.A. is continuing its investigation into two dozen cases that remain unexplained. Those cases, said a U.S. official briefed on the findings, offer the greatest chance of yielding clues to whether a foreign power is responsible for some of the unexplained health incidents that have plagued American diplomats and C.I.A. personnel in Havana and Vienna, among other cities.
In addition to those two dozen cases, a significant number of others remain unexplained, the official said.
The idea that Russia, China or Cuba was responsible for attacking hundreds of diplomats around the world was never backed up by any evidence that the Biden administration could unearth. But the F.B.I., the Pentagon and others continue to investigate whether a foreign power was involved in a smaller number of incidents, the U.S. official said. Clusters of incidents in Havana beginning in 2016 and some in Vienna in 2021, along with other individual incidents, remain a focus of such investigations.
The interim findings left many victims dissatisfied, particularly current and former officials who have been battling chronic ailments for years without being given a clear explanation. In a statement, a group of victims said the C.I.A. interim findings “cannot and must not be the final word on the matter.” The release of the findings, the victims said, was a breach of faith.
“The C.I.A.’s newly issued report may be labeled ‘interim’ and it may leave open the door for some alternative explanation in some cases, but to scores of dedicated public servants, their families and their colleagues, it has a ring of finality and repudiation,” the statement said.
William J. Burns, the director of the C.I.A., said the agency was pursuing a complex issue with “analytic rigor, sound tradecraft and compassion,” emphasizing that agency officers have experienced real symptoms.
“While we have reached some significant interim findings, we are not done,” Mr. Burns said in a statement. “We will continue the mission to investigate these incidents and provide access to world-class care for those who need it.”
The agency has never accused Russia or another power of being responsible, but some officials, particularly in the Pentagon, said they believed there was evidence of the involvement of Moscow’s spy agencies, and many victims concurred. When Mr. Burns traveled to Moscow in December to warn Russia against invading Ukraine, he raised the issue of the health incidents and said if Russia was found responsible, there would be consequences.
Marc Polymeropoulos, a former C.I.A. officer who suffered Havana syndrome symptoms on a trip to Moscow in 2017, said it was critical to continue to investigate the cases that remain unexplained. Praising Mr. Burns’s efforts to improve care for injured officers, he added that the C.I.A. should not revert to a culture where victims were denigrated and dismissed.
“It took us 10 years to find Osama bin Laden,” Mr. Polymeropoulos said. “I would just urge patience and continued investigation by the intelligence community and the Department of Defense.”
Another victim, who asked that his name not be used because of his work for the agency, said the government had erred by pushing for more people to report ill health or unexplained symptoms. That brought in thousands of extraneous cases, the victim said, making it harder for the agency’s analysts to focus on the real cases.
The government official briefed on the findings said the effort to bring in large numbers of reports was not a mistake because it allowed the United States to speed up treatment for people suffering from symptoms. The effort also helped provide needed treatment to people with previously undiagnosed conditions, officials said.
C.I.A. officials said there was agreement within the intelligence community about the finding that the majority of Havana syndrome incidents were not the work of an adversarial power conducting a sustained campaign around the globe. Still, confidence in that assessment ranged from low to high across various intelligence agencies.
In addition to the C.I.A., an expert panel has been looking at classified information about the incidents. The panel, which has provided its findings to the government but is still finishing its report, explored technologies that could result, at least theoretically, in the symptoms being reported.
When made public, that report is expected to provide information on whether directed energy or microwaves could account for some of the unexplained incidents.
A directed energy weapon remains the hypothesis that a number of victims who have studied the incidents believe is most likely. Some of these current or retired officials believe government investigators have dismissed evidence they have collected of strange sounds or electromagnetic readings.
But late last year, officials said the C.I.A. had been unable to find any evidence that a directed energy device was responsible, neither intercepting communications from a foreign government that suggested the use of such a device or readings showing the presence of microwaves at the location of an incident.
The Havana Syndrome Mystery
What is the Havana Syndrome? The mysterious illness, which has affected military officers, C.I.A. personnel and diplomats around the world, manifests itself in a host of ailments such as chronic headache, vertigo and nausea.
When was it first detected? Some former government officials say the episodes stretch back decades, but the first victims in this spate of incidents were a group of Americans working at the U.S. Embassy in Havana in 2016. Since then, U.S. officials in several countries have experienced symptoms.
What is the source of the illness? Some officials are convinced that the symptoms are caused by Russian microwave attacks, but there is so far no evidence to support the theory. Outside experts have also suggested that the condition could be a psychosomatic reaction to stress.
How is the U.S. addressing the issue? The Biden administration, Congress and other agencies have taken steps to investigate the episodes and provide support to victims. President Biden raised the issue with Russian President Vladimir Putin in a summit earlier this year.
Asked if directed energy or microwaves remain a leading theory for the cases still being investigated, an agency official said no potential explanation was being eliminated.
Of the cases that have been resolved, some had medical explanations, including previously undiagnosed conditions, while others were said to have had environmental causes, though C.I.A. officials did not offer examples. Some of the cases, officials said, were potentially related to the high stress of working at the C.I.A.
Some outside experts believe that stress has contributed to psychosomatic reactions or so-called functional illness. Many victims have found those explanations for chronic headaches and nausea offensive.
Last year, Congress passed a law compensating victims of Havana syndrome, and giving the government until April to devise a payment plan. It is not clear how the interim findings could affect that process. C.I.A. officials would say only that they were working on implementing the law, that their decisions were not yet due and that they were mindful of congressional intent to support officers reporting symptoms.
The statement by the victims said they hoped the interim report was not motivated by a desire on the government’s part to deny claims made under the act.
While some former officials said cases of similar injuries stretch back decades, the most recent spate of ailments began at the end of 2016, when C.I.A. officers and diplomats working in the U.S. Embassy in Havana reported strange sounds, pressure and then various ailments including nausea and debilitating migraine headaches.
Those incidents were followed by multitudes of reports in China, then in Vienna. Other reports have come in from around the world, including Russia, India and Vietnam.
A review released in 2020 by a team from the National Academies of Sciences, Engineering, and Medicine found that a microwave weapon was the most likely cause of the injuries. Victims of the attacks had frequently pointed to various reports over the years about Russian research into directed energy weapons and the capacity of microwaves to cause brain injuries. But critics said that effort was incomplete because the Trump administration had not given the team access to classified information.
Many senior Trump administration officials, including leaders at the C.I.A., viewed the incidents skeptically, arguing that the evidence was insufficient to conclude that the mysterious incidents were attacks or that Russia was behind them. Some of those officials were influenced by an F.B.I. report that concluded the ailments were a kind of functional illness or stress-induced psychosomatic response.
The Biden administration took office with Mr. Burns and others pledging to get better treatment for victims for what they called the anomalous health incidents. They also started new efforts to study what had happened. They formed a new scientific review panel, led by the intelligence agencies, to examine all of the evidence, classified and unclassified. The C.I.A. formed a new cell, led by a veteran of the effort to find bin Laden, to figure out what happened.
Last year, Mr. Burns and other officials said the agency was focused on some 200 cases that remained unexplained.
The agency is now focused on two dozen.