LONDON — Global health officials are closely following a new respiratory virus related to SARS that is believed to have killed at least one person in Saudi Arabia and left another person in critical condition in Britain.

The germ is a coronavirus, from a family of viruses that cause the common cold as well as SARS, the severe acute respiratory syndrome that killed some 800 people, mostly in Asia, in a 2003 epidemic.

In the latest case, British officials alerted the World Health Organization on Saturday of the new virus in a man who transferred from Qatar to be treated in London. He had recently traveled to Saudi Arabia and is now being treated in an intensive care unit after suffering kidney failure.

Health officials don’t know yet whether the virus could spread as rapidly as SARS did or if it might kill as many people.

“It’s still (in the) very early days,” said Gregory Hartl, a WHO spokesman. “At the moment, we have two sporadic cases and there are still a lot of holes to be filled in.”

Hartl said it was unclear how the virus spreads. Coronaviruses are typically spread in the air but Hartl said scientists were considering the possibility that the patients were infected directly by animals. He said there was no evidence yet of any human-to-human transmission.

So far there is no connection between the cases except for a history of travel in Saudi Arabia. SARS was first spread to humans from civet cats in China.

Hartl said no other countries have so far reported any similar cases to WHO.

Other analysts said it was unclear how dangerous the virus is.

“We don’t know if this is going to turn into another SARS or if it will disappear into nothing,” said Michael Osterholm, a flu researcher at the University of Minnesota. He said it was crucial to determine the ratio of severe to mild cases.

SARS hit more than 30 countries worldwide after spreading from Hong Kong. Osterholm said it was worrying that at least one person with the disease had died. “You don’t die from the common cold,” he said. “This gives us reason to think it might be more like SARS,” which killed about 10 percent of the people it infected.

Britain’s Health Protection Agency and WHO said in statements that the 49-year-old Qatari national became ill on Sept. 3, having previously traveled to Saudi Arabia. He was transferred from Qatar to Britain on Sept. 11 and is being treated in an intensive care unit at a London hospital for problems including kidney failure. Respiratory viruses aren’t usually known to cause serious kidney problems.

The Health Protection Agency said it was unaware of any ties the patient had to Britain and that he likely was in a private clinic in the Middle East before being transferred to the London hospital. It said none of the health workers involved in his treatment had fallen ill.

WHO said virus samples from the patient are almost identical to those of a 60-year-old Saudi national who died earlier this year. The agency isn’t currently recommending travel restrictions and said the source of infection remains unknown.

Saudi officials said they were concerned the upcoming Hajj pilgrimage next month, which brings millions of people to Saudi Arabia from all over the world, could provide more opportunities for the virus to spread.