In Wednesday's online issue of the medical journal The Lancet, French researchers analyzed data on 55 of 64 laboratory-confirmed cases of Middle East respiratory syndrome (MERS) worldwide as of June 20.
"Our analysis suggests that MERS-CoV does not yet have pandemic potential," concluded Arnaud Fontanet of the Pasteur Institute in Paris and his co-authors.
Their statistical analysis helps determine whether each infected person will infect more than one person, said Chris Bauch, a professor of applied mathematics at the University of Waterloo who wrote a journal commentary on the study.
The measurement is called the basic reproduction number or R value.
"If each infected person infects one person on average then it will die out," Bauch said.
If the R value is greater than 1.0, then cases can grow exponentially and cause a full-blown pandemic.
In the worst case scenario in Fontanet's study, the MERS coronavirus had an R value of 0.69 compared with 0.80 when SARS was prepandemic.
The SARS coronavirus infected more than 8,000 people worldwide in 2002 and 2003 and 774 deaths were linked to it.
When SARS reached an epidemic level in many widespread countries — a pandemic — its R value was estimated at between 2.2 and 3.7. SARS also reached that level in months, while the MERS coronavirus has been circulating for more than a year.
SARS, MERS and the common cold are coronaviruses with similarities and differences in how they seem to infect human airways and cause illness in humans.
Part of the problem in assessing the pandemic potential of MERS is that the number of secondary infections, or how many people are infected by a single case, is so variable, Bauch said.
"The conclusion of this study is that the MERS Co-V virus as we currently understand it, as we currently know it, does not have the potential to cause a pandemic. However, we need to continue being vigilant, continue refining our mathematical calculations and, of course, public health needs to continue doing the great job it's doing to stay on top of this," Bauch said.
It is also possible that milder causes of MERS have gone undetected, which would raise estimates of the R value, the French researchers said.
Public health experts and researchers also need to consider factors such as how viruses can mutate to enter the body more easily or not, and how different seasonal conditions could affect transmission.
MERS patient dies in London
On Wednesday, a British hospital announced that a man infected with MERS had died in hospital.
"Guy's and St Thomas' can confirm that the patient with severe respiratory illness due to novel coronavirus sadly died on Friday 28 June, after his condition deteriorated despite every effort and full supportive treatment," the hospital said in an emailed statement.
The man was flown to St Thomas' Hospital in London from Qatar in September last year, BBC News reported.
The World Health Organization says more than 40 people have died from MERS.