U.S. intelligence agencies may have ruled out the idea that a rash of mysterious illnesses plaguing American diplomats and other officials is part of a sustained campaign by one of Washington's adversaries, but they now say that in a small number of cases the only likely explanation is the use of some sort of weapon.
A report released Wednesday by a panel of experts assembled by U.S. intelligence officials finds that the core symptoms in these cases are "distinctly unusual and unreported elsewhere in the medical literature," making it highly unlikely the cause could be natural.
"Pulsed electromagnetic energy, particularly in the radiofrequency range, plausibly explains the core characteristics," the report said.
"Sources exist that could generate the required stimulus, are concealable, and have moderate power requirements," the report added. "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."
The mystery illness was first reported in 2016 among diplomats and other employees at the U.S. Embassy in Havana, Cuba.
Since then, hundreds of cases have been reported in Russia, China, Poland, Austria and elsewhere, with symptoms ranging from nausea and dizziness to debilitating headaches and memory problems.
The U.S. government has been engaged in a yearlong effort to find the source of the anomalous health incidents, or AHI, commonly called Havana Syndrome.
An interim report issued last month by the U.S. Central Intelligence Agency (CIA), concluded most of the cases "can be reasonably explained by medical conditions or environmental and technical factors, including previously undiagnosed illnesses."
However, it warned that a smaller number of cases continued to defy explanation and that, in those cases, officials "have not ruled out the involvement of a foreign actor."
Wednesday's report appears to support that conclusion, though officials said the latest effort was not focused on assigning responsibility for the possible attacks.
"There are a small number of the cases we looked at that had no other plausible mechanism," according to one U.S. intelligence official familiar with the expert panel's work who spoke to reporters on the condition of anonymity.
Exactly how the possible attacks were carried out, though, remains a mystery.
"We don't have a specific device," said a second official, who like the first was familiar with the panel's work.
But the official said the idea that some cases of Havana Syndrome are the result of a weapon of some sort is "more than a theory."
"We had accounts of people that had been around RF [radio frequency] energy inadvertently and describe symptoms like that," the official added.
The notion that a directed, pulsed radio frequency mechanism was behind key symptoms of Havana Syndrome — the quick onset of pain or problems with the inner ear, including a loss of balance, dizziness and nausea — was first raised in 2020 the National Academy of Sciences, which called such as source "the most plausible mechanism in explaining" the growing number of cases.
Wednesday's report affirmed that finding, but also left open the possibility that some of the cases could have been caused by a device using ultrasound technology, though it said an ultrasonic device would only be able to produce the right combination of symptoms if deployed in close proximity to the victim.
In a statement Wednesday, the U.S. Director of National Intelligence Avril Haines and CIA Director William Burns said the effort to determine the cause of Havana Syndrome is making progress.
"We continue to pursue complementary efforts to get to the bottom of Anomalous Health Incidents (AHIs) — and to deliver access to world-class care for those affected," they said in a statement.
"We will stay at it, with continued rigor, for however long it takes," they added. "Nothing is more important than the wellbeing and safety of our colleagues."
Officials familiar with the work on Havana Syndrome said Wednesday "it's frustrating" not being able to get a clear-cut, definitive answer as to what has happened to as many as a couple of dozen of their colleagues and U.S. diplomatic personnel.
But they said that despite the many unknowns, the latest findings do offer hope for those who have been impacted.
"We've learned a lot," one of the officials said. "While we don't have the specific mechanism for each case, what we do know is if you report quickly and promptly get medical care, most people are getting well."
The report also recommended the U.S. create a central database to collect information on future reported cases, develop a set of so-called "bio-markers" to better identify new cases, try to develop technology capable of detecting an attack, and improve communications.
The White House Wednesday welcomed the report's findings.
"The [experts] panel undertook a rigorous, multi-disciplinary study that has identified important findings and recommendations," a National Security Council spokesperson said in a statement.
The findings "will inform intensive research and investigation moving forward as we continue our government-wide effort to get to the bottom of AHI," the spokesperson added.
U.S. President Joe Biden on Tuesday named a top official to lead the government's interagency response to Havana Syndrome.