The mysterious condition known as Havana syndrome can be “plausibly explained” by the targeted use of “pulsed electromagnetic energy”, according to a partially declassified US intelligence report. First reported by American and Canadian diplomats in the Cuban capital in 2016, "Havana syndrome" consists of an array of strange neurological symptoms and has led to debates over whether the illness could be caused by some sort of human-made device.

A panel of intelligence community experts with “expertise in relevant areas of science, medicine, and engineering” composed the report after analyzing over 1,000 documents and interviewing affected individuals. They determined the symptoms associated with the illness to be “genuine and compelling”, and noted that while some cases can be attributed to known psychological or medical factors, others remain unexplained.

The authors sought to determine the feasibility of five potential causal mechanisms, including “acoustic signals, chemical and biological agents, ionizing radiation, natural and environmental factors, and radiofrequency and other electromagnetic energy.” To narrow down the scope of the investigation, they assessed the potential of each of these mechanisms to account for cases of Havana syndrome that cannot be easily explained by other means.

More specifically, they looked at cases involving a combination of four particularly puzzling “core characteristics.” These include “the acute onset of… sound or pressure in only one ear or on one side of the head,” as well as vertigo, “a strong sense of locality or directionality,” and an absence of any obvious environmental or medical causes for such symptoms.

Ruling out the possibility that Havana syndrome could represent an underlying brain disorder, the authors state that “the combination of the four core characteristics is distinctly unusual and unreported elsewhere in the medical literature, and so far have not been associated with a specific neurological abnormality.”

On the other hand, they conclude that “pulsed electromagnetic energy, particularly in the radiofrequency range, plausibly explains the core characteristics,” although they do concede that such a theory is riddled with “information gaps.” Addressing the possibility that Havana syndrome could therefore be caused by a nefarious device, they go on to explain that devices do "exist that could generate the required stimulus, are concealable, and have moderate power requirements," that could produce the observed symptoms. 

For example, they reveal how, “using nonstandard antennas and techniques, the signals could be propagated with low loss through air for tens to hundreds of meters, and with some loss, through most building materials.” At the same time, however, the authors point out that their report does not provide evidence for the use of any such device, nor does it address the issue of who may be behind any hypothetical attack.

With the possible exception of ultrasound devices, the report rules out the plausibility of all other proposed causes. For example, both ionizing radiation and chemical or biological agents tend to produce effects that are inconsistent with the symptoms of Havana syndrome.

Interestingly, these findings appear to contradict those of a recent CIA investigation which concluded that most cases of the illness can be explained by natural causes, and that claims of a targeted attack by any foreign state are unsubstantiated.

In a statement, the authors of this latest report said that “moving forward, the work of the IC [Intelligence Community] Experts Panel will help sharpen the work of the IC and broader U.S. Government as we focus on possible causes.

“We will stay at it, with continued rigor, for however long it takes.”