In late 2016, two dozen US government workers deployed to the embassy in Havana, Cuba, began suffering mysterious neurological symptoms.

In 2018, embassy workers at the US consulate in Guangzhou, China started exhibiting similar brain-related symptoms and had to be brought home.

Some reported hearing high-pitched sounds while at home or staying in hotels, leading to an early theory of a sonic attack.

Now a new report has shed light on the “most plausible” explanation for symptoms, which included intense head pressure, headaches, dizziness, nausea, bloody noses, cognitive difficulties and mild brain injury.

An investigation by the US National Academies of Sciences, Engineering, and Medicine found the symptoms suffered by those with the so-called Havana syndrome were consistent with the effects of “directed, pulsed, radiofrequency energy”.

In other words, directed microwave radiation. 

Simply put, microwaves heat food by exposing it to the same electromagnetic waves that are used at lower frequencies in broadcast radio or television.

The radio frequency energy of radiation, as mentioned in the report, includes radio waves and microwaves that can have adverse effects on the electrochemical balance of the brain when directed at humans.

Russia has long been suspected of using a covert sonic weapon that produces microwave radiation to damage victims’ brains.

The US government-commissioned report did not name a source for the energy and did not say it came as the result of an attack.

Most cases of Havana syndrome have arisen from the US Embassy in Havana. Photo: Getty

But it did note that previous research into the effects of pulsed radio frequency energy was done in the former Soviet Union more than 50 years ago. 

Their findings come more than a month after concerns were raised that two US officials from the CIA who visited Australia late last year and were said to have suffered symptoms consistent with Havana syndrome may have been targeted by Russian microwave weapons.

The 19-member committee involved in the US study also assessed if an infection, toxic chemicals or psychological factors could explain the symptoms, and found “directed, pulsed, radiofrequency energy” was the “most plausible mechanism in explaining these cases among those that the committee considered”.

“The committee cannot rule out other possible mechanisms and considers it likely that a multiplicity of factors explains some cases and the differences between others,” the report said, noting that it faced significant challenges in trying to get to the bottom of the medical mystery.

About 40 State Department staff who served at the embassies in Cuba and China between 2016 and 2018 were affected by Havana syndrome.

They experienced everything from ear pain, intense head pressure or vibration to dizziness, visual problems, and cognitive difficulties.

“Many still continue to experience these or other health problems,” a statement by study authors read.

A further 14 Canadian diplomatic staff members at the embassy in Cuba fell ill with Havana syndrome between 2017 and 2019.

Among them, not everyone reported the same symptoms and the National Academy of Sciences research did not have access to all the previous studies on the illnesses, some of which are classified.

“The committee found these cases quite concerning, in part because of the plausible role of directed, pulsed radiofrequency energy as a mechanism, but also because of the significant suffering and debility that has occurred in some of these individuals,” said committee chairman David Relman, a professor of medicine at Stanford University.

He concluded: “We as a nation need to address these specific cases as well as the possibility of future cases with a concerted, co-ordinated and comprehensive approach.”