Researchers recently identified an aggressive new strain of human immunodeficiency virus in Cuba that advances to Aids much faster than the average strain, but this variant of the virus may be the most aggressive ever studied in humans.

Other fast-acting variants of HIV exist, but the Cuban strain is the first in which all observed patients infected with a particular strain of HIV progress to Aids at the accelerated rate, Anne Mieke Vandamme, the researcher from the Catholic University of Leuven in Belgium who published findings on the Cuban strain, told The Independent.

“The difference is that with most clades, only a minority of patients infected with a virus from that clade progress so fast,” Dr Vandamme said, using the word clade to mean subtype of HIV. “Here, all patients in our cohort infected with a virus from the CRF19 variant progress to Aids within 3 years. This is the first variant where this has been noted.”

Only 73 patients have been studied so far, but the 73 progressed to Aids within a median time of 1.4 years after being infected with HIV. The average HIV strain advances to Aids within a median time of 9.8 years.

Still, the small sample size means that researchers have a lot left to learn about the new strain. Dr Vandamme said her team is collecting data on 144 cases after the initial study.

“We indeed did not have so many CRF19-infected patients in the cohort, but the difference was so striking that even with this small sample size the effect was very significant,” Dr Vandamme said. “This means the difference is huge. Of course this needs to be repeated in a much larger sample size to verify if the results will hold. However, we felt that we had to publish now already.”

Cuban clinicians reportedly were worried about the aggressive strain of HIV and asked Dr Vandamme’s team to investigate. Despite the rapid progression, she said the virus is spreading slowly and does not yet pose a health threat in Cuba or the rest of the world, but it is possible it could spread.

“I suspect it would need to reach even higher levels in Cuba before we should start fearing that it will spread to other countries, this may take many years or not happen at all,” she said. “But with virus spread, a chance event can make all the difference, you just need one patients taking this virus out of Cuba and passing it on abroad, where it could spread further.”

As of 2013, some 15,000 people in Cuba were living with HIV, out of about 11.3 million, according to the United Nations.