"Although this case provides strong evidence for person to person transmission, the risk of infection in most circumstances is still considered to be very low," John Watson, head of the respiratory diseases department at the Health Protection Agency, said in a statement. "If (the) novel coronavirus were more infectious, we would have expected to have seen a larger number of cases."
The new coronavirus is part of a family of viruses that cause ailments including the common cold and SARS. In 2003, a global outbreak of SARS killed about 800 people worldwide.
Officials at the World Health Organization said the new virus has probably already spread between humans in some instances. In Saudi Arabia last year, four members of the same family fell ill and two died. And in a cluster of about a dozen people in Jordan, the virus may have spread at a hospital's intensive care unit.
"We know that in some of those cases there was close physical contact between family members caring for one another, so we can't rule out human-to-human transmission," said Gregory Hartl, a WHO spokesman.
He said there were still big gaps in the understanding of the novel coronavirus, which can cause acute pneumonia and kidney failure. Of the 11 cases to date, five people have died.
Health experts still aren't sure how humans are being infected. The new coronavirus is most closely related to a bat virus and scientists are considering whether bats or other animals like goats or camels are a possible source of infection.
WHO says the virus is probably more widespread than just the Middle East and has advised countries to test any people with unexplained pneumonia.