US officials said Wednesday the Vietnam leg of US Vice President Kamala Harris' South Asia trip had to be delayed by a few hours due to reports of two US diplomatic personnel coming down with the mysterious combination of ailments that have come to be known as Havana Syndrome.

The US Embassy in Hanoi announced there had been a "possible anomalous health incident in Hanoi," the phrase Washington has used regarding other possible Havana Syndrome cases. Havana Syndrome is named after the city in Cuba where the incidents first occurred.

While the investigation remains in its early stages, the two US officials affected by the incidents have been medically evacuated from Vietnam. The incidents are alleged to have occurred within the last week.

White House spokeswoman Jen Psaki said no one on Vice President Harris' staff was involved nor was anyone who worked for the White House.

Psaki said, "there was an assessment done of the safety of the vice president, and there was a decision made that she could continue travel along with her staff."

What is Havana Syndrome?

Havana Syndrome is the name given to a series of mysterious health incidents that have plagued US diplomatic personnel, first in the Cuban capital of Havana and then in various cities around the world, including in Washington.

US diplomats have reported first hearing a loud piercing sound before feeling an intense amount of pressure in the face. After that, they reported pain, dizziness, nausea, migraines and even memory loss.

The incidents began in 2016 and have since been reported in Germany, Austria, Russia, and China.

Do we know what causes Havana Syndrome?

There is currently no known cause for Havana Syndrome nor has a culprit been identified. It is not yet even clear to US officials if these incidents are in fact attacks.

While there is rare bipartisan support in both houses of Congress for the ongoing government-wide investigation, as well as support for those affected by Havana Syndrome to receive medical attention, publicly not much beyond informed speculation pointing towards Russia is known at present. Moscow has denied involvement and knowledge in the potential attacks.

Targeted microwaves or sonic attacks are among the theories floated to explain the combination of noise followed by mysterious medical ailments. Another theory is that the cases are a biproduct of an espionage operation or hacking effort aimed at the US government.

Harris seeks to reassure allies in Asia 

Vice President Harris is in Vietnam to shore up support for US allies and offer reassurances as the chaotic airlift of US citizens, NATO allies and Afghans associated with the West from Kabul airport continues.

A donation of one million more BioNTech-Pfizer vaccine doses and the opening of an office of the US Centers for Disease Control and Prevention in Hanoi topped her agenda prior to the news of possible cases of an "anomalous health incident" among US personnel in the country.

While visiting the US Embassy to sign a lease on a new embassy in Vietnam, Harris did not directly mention the new possible Havana Syndrome cases, but she did offer gratitude and support for US personnel stationed there.

"Here's my message to embassy staff: thank you," she said. "The people who work in our embassies around the world are extraordinary public servants who represent the best of what the United States believes itself to be and aspires to be, which is a good neighbor for our partners and our allies around the globe."

Harris also laid a wreath amid a downpour at the monument to where the late Senator John McCain's airplane was shot down over then North Vietnam on the third anniversary of his death from brain cancer.

ar/nm (AFP, AP, dpa)