The new MERS coronavirus currently doesn’t spread well enough among people to trigger a pandemic, says a new study that calculates the rate at which the virus is transmitting person to person.
But the senior author says the pattern of how the virus is spreading now cannot be used to predict whether MERS will become a bigger threat in the future.
“There is absolutely no guarantee that this virus will stay as it is. It could very well follow the same path as SARS did 10 years ago,” Dr. Arnaud Fontanet, who heads the emerging diseases epidemiology unit at the Institut Pasteur in Paris, said in an interview.
Others too say the study should not be used to write off the new virus.
“The virus has shown a potential for human-to-human transmission. And whether such transmission is sustained depends on the intensity of control measures as well as the characteristics of the people involved in transmission,” said Marc Lipsitch, an infectious diseases specialist who teaches at Harvard University.
“For that reason, I think it’s premature to say that this virus does not present a pandemic threat.”
The study, published in the journal The Lancet, analyzes what is known about how often people who have been infected with the MERS virus spread it to one or more other people. The authors used the data to calculate what is called the basic reproduction number, known in the parlance of infectious diseases as the R nought.
In order for a disease to achieved sustained spread, the average infected person must spread a bacterium or virus to at least one other person. That is an R nought of one. A pathogen with a basic reproduction number of less than one would peter out.
The measles virus, which is very contagious, has a basic reproductive number of between 12 and 18, meaning that among people who are susceptible to the virus, each infected person would be expected to pass the virus to between a dozen and 18 other people. In a 2003 study in the journal Science, Lipsitch and colleagues estimated the R nought of SARS to be three.
Using the publicly available data on MERS cases, Fontanet and his co-authors set out to figure out what the basic reproduction number for the new coronavirus has been to date.
There are many holes in the available data. For instance, Saudi Arabia, which is responsible for 63 of the 77 confirmed MERS cases, often does not disclose if new infections have links to previous ones – which might mean they caught the virus from another person – or are what are called sporadic cases, people thought to have been infected by an animal or exposure to the virus in the environment.
The authors tried to work around the gaps by calculating best- and worst-case scenarios. Both, it turns out, came up with a reproductive number of less than one, which suggests the virus doesn’t yet have pandemic potential, they said. Those rates were 0.60 and 0.69 respectively.
The authors noted that in the early stages of SARS it had a reproductive number of 0.80, closer to one than what is currently seen with the MERS virus. But they suggested that even though the viruses are cousins, people should be cautious about drawing too many comparisons because the viruses are different and have cropped up in different parts of the world.