US vice president Kamala Harris had her trip to Vietnam delayed due to two suspected cases of an unknown ailment afflicting diplomatic staff and family members at international postings.
First reported in Cuba and now with potential cases numbering in the hundreds, multiple US government agencies are investigating what, and potentially who, could be causing the illness.
Some staff members believe the government isn't prioritizing the sickness and worry about their safety while abroad.
And it's not helping the already tense relationship between the US and Cuba.
Here's what we know about "Havana Syndrome" so far and why authorities are so concerned about it.
What is Havana Syndrome?
The first cases of the mystery illness were reported in 2016 by diplomats and relatives stationed in Cuba. But doctors are unsure of the root cause, making it difficult to fully treat those suffering from the ailment.
Government officials from the US and Canada, as well as some of their family members, have experienced dizziness, memory loss and nausea among other issues. Many said they heard a loud sound before the onset of the illness. Some have even been forced to resign due to the severity of their symptoms.
A 2020 report from the National Academies of Science, Engineering and Medicine determined the cases they looked into were unlike any existing medical disorders and that not all people suffering from the so-called "Havana Syndrome" experienced the same symptoms.
What causes it?
There are multiple theories surrounding the root cause of Havana Syndrome. Those include exposure to certain chemicals, infectious diseases and psychological issues.
However, the government report from last year determined the cause to be "consistent with the effects of directed, pulsed radio frequency (RF) energy".
When Dr James Lin, professor emeritus at the University of Illinois at Chicago, first heard about the illness, he thought it sounded strikingly similar to his research on microwave energy.
He says a clear indicator to him was that only certain people noticed symptoms after hearing a loud sound.
"The unique aspect of this is that those people who had reported this phenomena, said that there were other people in the room but they had no idea except for the person reporting it," Lin says.
According to Lin, the effects of this type of energy can occur instantaneously, and the technology used to transmit it is fairly mobile, even small enough to fit inside a car.
Dr Jeffrey Staab at the Mayo Institute served on the committee that published the government report. He says on top of the physical symptoms present in patients, there is also a psychological effect.
"Regardless of the sort of core symptoms ... the uncertainty of the diagnosis, the inconsistent, or conflicting diagnoses that they received from different places and different physicians that they saw, the partial response to the treatments that they received all add a level of psychosocial burden," he says.
The report says the investigation was delayed because the cases were not initially linked to each other. The committee was further limited by a lack of access to certain information due to government confidentiality.
Previous medical reports also proposed some cases could be the result of a "mass psychogenic illness". That occurs when stress and fear surrounding an outbreak or unknown disease subconsciously trigger people to begin noticing symptoms in their bodies.
How widespread is it?
We don't know exactly how many documented cases there are, due to the classified nature of the work.
But in July, US Secretary of State Antony Blinken said more than 200 possible cases of the illness have been reported.
Two years after the first cases in Havana, the US State Department began investigating similar cases at its diplomatic post in Guangzhou, China.
Earlier this year, the New Yorker reported more than 20 possible cases were being investigated in Vienna.
The suspected attacks haven't been limited to outside of US borders. At least two potential incidents were identified in the Washington area.
Why has it got authorities so concerned?
The discovery of the mysterious medical cases has strained the thawing relationship between the US and Cuba. The US significantly downsized its Havana embassy staff and even expelled Cuban officials from the embassy in Washington. Canada has also pulled some diplomats out of Cuba.
The Cuban government has repeatedly rejected that it is behind the illness or that it knows who is behind the alleged attacks.
According to a government statement:
Since the Cuban Revolution during the 1950s, the US has enacted several policies to distance itself from Cuba and severely limit the communist country's economic capacity.
During the Obama administration, US restrictions were eased significantly, allowing Americans to visit the island more easily and reopening embassies in Havana and Washington. This progress could now be in limbo.
So what has one of the men who hunted down Osama Bin Laden got to do with it?
US administrations have approached the matter differently. Donald Trump outright blamed the Cuban government for its involvement.
Joe Biden and his team have inherited the issue with more suspected cases popping up around the world, including the two that delayed Harris' trip. Government agencies, like the State Department and CIA, have set up task forces to investigate Havana Syndrome.
The Wall Street Journal reported a senior CIA official who was involved with the hunt for Osama bin Laden will take up the reins of the investigation.
The issue is also being taken up in Congress. A bill called Helping American Victims Afflicted by Neurological Attacks (HAVANA) Act passed the Senate and is now being discussed in the House.
It authorizes the CIA, the State Department and other agencies to provide payments to personnel who incur brain injuries from hostilities while on assignment.
In an interview with NBC News, Secretary of State Antony Blinken said:
"The President has ordered that we make an intensive whole-of-government investigation to try to get to the bottom of this," he said.
The US maintains a travel advisory against its citizens visiting Cuba, due to Havana syndrome and the risk of Covid-19.
The US embassy in Havana is still operating with limited personnel, and family members are unable to accompany staff.
Further complicating the already strained relations are recent protests in Cuba. The US has publicly condemned the government's crackdown against the demonstrations and announced new sanctions against Cuba.
Cuba rejects the criticism of its human rights record.
[Bruno tweet]As investigations continue into the origin of Havana Syndrome, it appears the relationship between Cuba and the US will continue to remain icy at best.
On top of that, the mystery surrounding the sickness' cause and ways of managing it persist. The best the US government and Lin can do for now is speculate what's causing so many people to get sick.
"No one knows for sure," the professor says.
"The only people who can tell us and let us know for sure is who did it, and we don't know who has done it."
