[7] Most of the affected individuals reported an acute onset of neurological symptoms associated with a perceived localized loud sound such as screeching, chirping, clicking, or piercing noises.

[6] A 2023 review article written by Bartholomew and Baloh concluded that the AHIs are an example of mass psychogenic illness, rooted in a moral panic based on the fear of the Russians or Cubans attacking the U.S..

The authors stated that Havana Syndrome is "a socially constructed catch-all category for an array of pre-existing health conditions, responses to environmental factors, and stress reactions that were lumped under a single label".

[35] Beginning in late 2017, suspected attacks targeting U.S. intelligence personnel were reported in an expanding set of locations around the world,[36] including Moscow, Russia; Tbilisi, Georgia; Poland; Taiwan; and Australia.

[58] In September 2021, the CIA station chief in Vienna (the top U.S. intelligence officer in the country) was recalled over concerns over his management; he had been criticized for not taking quicker action in response to the Havana syndrome cases at his post.

The first, internally released in January, was a non-public report by the FBI's Operational Technology Division which found no evidence of a sonic attack or involvement of foreign adversaries.

[18] At the U.S. government's request, University of Pennsylvania (UPenn) researchers examined 21 affected diplomats posted to Cuba, and the preliminary results were published in the Journal of the American Medical Association (JAMA) in March 2018.

The editorial said that the UPenn study's conclusion (that the subjects suffered brain injuries) was flawed, because there were other (non-injury) explanations that were consistent with the symptoms, such as functional disorders, persistent postural-perceptual dizziness, or psychogenic causes.

In the board's view, "Allowing such confused and conflicting explanations of methodology and analysis to pass unchallenged is a slippery path for science, and dangerous for society at large".

[88][89] Stubbs and Montealegre wrote, "the causes of the health problems reported by embassy personnel are beyond the scope of this paper" and called for "more rigorous research into the source of these ailments, including the potential psychogenic effects, as well as possible physiological explanations unrelated to sonic attacks.

The report concluded "The evaluations conducted thus far have not identified a mechanism of injury, process of exposure, effective treatment, or mitigating factor for the unexplained cluster of symptoms experienced by those stationed in Havana."

The CDC decided not to conduct a retrospective case–control study because of the length of time between the event and the onset of symptoms, which could lead to recall and selection biases that "could generate misleading or obscured findings".

[39] Christopher C. Miller, who was acting defense secretary at the time, said in 2021 that "I knew CIA and Department of State were not taking this shit seriously and we wanted to shame them into it by establishing our task force.

The committee noted that lack of information and direct evidence (such as medical testing data about affected persons) limited what it could conclude about the phenomenon, and that "each possible cause remains speculative" and that "the report should not be viewed as conclusive".

[112] A New York Times investigation found that the State Department had "produced inconsistent assessments of patients and events, ignored outside medical diagnoses and withheld basic information from Congress".

The report determined that prior analyses by United States scientists were biased and relied on evidence that was cherry-picked to support the narrative of attacks by a foreign adversary.

[12][12] According to two unnamed officials interviewed by Politico, "While investigators have not determined definitively that these incidents are caused by a specific weapon, some believe any such device would be primarily transported by vehicle", and "Some could be small enough to fit into a large backpack, and an individual can be targeted from 500 to 1,000 yards away.

[59] Also in September, it was reported that multiple anecdotes from various Western diplomats stationed overseas, including in Russia, describe mysterious ailments during past decades that might be due to microwave devices.

The officials also said that the investigative efforts were 'extremely aggressive' and involved "a high degree of risk", and "Intelligence officers vigorously studied what happened in the hours, days and weeks surrounding the incidents...

"[135] Politico summarized the results by saying, "The finding undercuts a years-long narrative, propped up by more than a thousand reports from government employees, that a foreign adversary used pulsed electro-magnetic energy waves to sicken Americans.

Reuters also reported that "Cuba has for years labeled as 'science fiction' the idea that 'Havana Syndrome' resulted from an attack by a foreign agent, and its top scientists in 2021 found no evidence of such allegations.

[84] The journal Applied Radiology summarized the results as finding "no significant evidence of MRI-detectable brain injury, nor differences in most clinical measures compared to controls".

The journalists interviewed persons that stated that some AHIs were possibly caused by actions of Russian military intelligence,[146][147][148] specifically that members of the GRU Unit 29155, known for undertaking foreign operations, received awards and promotions for work related to the development and deployment of "non-lethal acoustic weapons".

[147] The journalists also interviewed sources that stated that telephone and travel records of some GRU agents matched the locations where a few U.S. personnel in China and Georgia reported AHIs.

The panel addressed the microwave hypothesis directly, writing, "No known form of energy can selectively cause brain damage (with laser-like spatial accuracy) under the conditions described for the alleged incidents in Havana.

"[118] After release of the March 2023 U.S. intelligence agencies' report which concluded that "available intelligence consistently points against the involvement of US adversaries in causing the reported incidents" and that a foreign adversary's involvement was "very unlikely", Cuba's Vice Foreign Minister Carlos Fernandez de Cossio told Reuters, "The unfortunate thing is the U.S. government leveraged [Havana syndrome] to derail bilateral relations ... and discredit Cuba."

The Reuters article reported that "Cuba has for years labeled as 'science fiction' the idea that 'Havana Syndrome' resulted from an attack by a foreign agent, and its top scientists in 2021 found no evidence of such allegations.

[39] The Senate Intelligence Committee leadership said in 2021 that it was working with the CIA on connection with the AHI investigation, saying, "We have already held fact finding hearings on these debilitating attacks, many of which result in medically confirmed cases of Traumatic Brain Injury, and will do more.

[171] In 2021, Congress passed the Helping American Victims Afflicted by Neurological Attacks (HAVANA) Act, which authorized the CIA director and the secretary of state to provide financial support for personnel with brain injuries.

[175][176][177][178] In March 2023, Politico reported that the U.S. Army funded a $750,000 grant to Wayne State University for a study to expose 48 ferrets to RF waves, comparing the effects to those from a control group of ferrets; the Department of Defense described the project as an attempt to "develop and test a novel laboratory animal model to mimic mild concussive head injury" similar to those reported by the embassy personnel in Havana and China.