Two separate research teams in New York have said the coronavirus circulating in the city likely came to the US from Europe.

The research teams at some of the largest hospitals in New York mapped out the virus' genetic code and compared it to existing sequences around the world.

Experts have been publicly sharing full genome sequences of the coronavirus that causes COVID-19 to look for how it mutates and understand how it has spread across the world. The genome sequence is composed of all the chemical letters that make up the protein and RNA of the virus.

"As viruses evolve during transmission from person to person, their sequences can help researchers to zero in on the provenance, or place of origin, of that specific infection,” said Matija Snuderl, director of molecular pathology at New York University (NYU)'s Grossman School of Medicine, where one of the studies was carried out.

The team at NYU used samples from 91 patients at three separate hospitals and determined that the virus had been circulating in New York for at least a couple of months.

They also found that most of the virus codes showed that they originated in Europe.

A separate team of researchers at Mount Sinai, one of the largest hospital systems in the United States, sequenced 90 coronavirus genomes from 84 patients who tested positive for COVID-19.

Those samples primarily came from US and European sources, the team concluded, in research that was released before peer review, as most new studies of coronavirus.

“These results show that SARS-CoV-2 came to the New York City area predominantly via Europe through untracked transmissions." said Dr Viviana Simon, a professor of microbiology and infectious diseases at Mount Sinai’s Icahn School of Medicine.

“The study also suggests that the virus was likely circulating as early as late-January 2020 in the New York City area.”

Just one of the cases studied appeared to come from Asia and it was most closely related to the virus samples from the outbreak in Seattle, Washington State.

Institut Pasteur note few mutations

Etienne Simon-Lorière, who is the head of Institut Pasteur’s department for evolutionary genomics of RNA Viruses said the findings were not very surprising but noted the difficulty of determining when the novel coronavirus began circulating in many countries.

“The genome of the virus is very stable so there are very few mutations that we see today,” Simon-Lorière told Euronews. This means that determining the date the virus began circulating in a community is a “delicate” process and not certain.

“But it’s true that the viruses that are circulating in the United States, that we’ve seen in other US states, resemble those that we find in Europe.”

New York has become the epicentre of the coronavirus outbreak in the United States. There are over 87,000 cases in the city alone and nearly 5,000 people have died, according to the NYC Department of Health.

In late January, the US prohibited foreign nationals who had been to China in the previous 14 days from entering the country. Americans who had been to China were told to self-quarantine.

But the US president announced a ban on travel from Europe much later - in mid-March - as several European countries were enacting lockdown policies themselves.