How contagious is the Wuhan coronavirus and can you spread it before symptoms start?
- Written by C Raina MacIntyre, Professor of Global Biosecurity, NHMRC Principal Research Fellow, Head, Biosecurity Program, UNSW
Cases of the Wuhan coronavirus have increased dramatically over the past week, prompting concerns about how contagious the virus is and how it spreads.
According to the World Health Organisation, 16-21% of people with the virus in China became severely ill and 2-3% of those infected have died.
Read more: The Wuhan coronavirus is now in Australia – here's what you need to know
A key factor that influences transmission is whether the virus can spread in the absence of symptoms – either during the incubation period (the days before people become visibly ill) or in people who never get sick.
On Sunday, Chinese officials said transmission had occurred during the incubation period.
So what does the evidence tell us so far?
Can you transmit it before you get symptoms?
Influenza is the classic example of a virus that can spread when people have no symptoms at all.
In contrast, people with SARS (severe acute respiratory syndrome) only spread the virus when they had symptoms.
No published scientific data are available to support China’s claim transmission of the Wuhan coronavirus occurred during the incubation period.
However, one study published in the Lancet medical journal showed children may be shedding (or transmitting) the virus while asymptomatic. The researchers found one child in an infected family had no symptoms but a chest CT scan revealed he had pneumonia and his test for the virus came back positive.
Yuan Zheng/AAPThis is different to transmission in the incubation period, as the child never got ill, but it suggests it’s possible for children and young people to be infectious without having any symptoms.
This is a concern because if someone gets sick, you want to be able to identify them and track their contacts. If someone transmits the virus but never gets sick, they may not be on the radar at all.
It also makes airport screening less useful because people who are infectious but don’t have symptoms would not be detected.
How infectious is it?
The Wuhan coronavirus epidemic began when people exposed to an unknown source at a seafood market in Wuhan began falling ill in early December.
Cases remained below 50 to 60 in total until around January 20, when numbers surged. There have now been more than 4,500 cases – mostly in China – and 106 deaths.
Read more: Coronavirus outbreak: WHO's decision to not declare a global public health emergency explained
Researchers and public health officials determine how contagious a virus is by calculating a reproduction number, or R0. The R0 is the average number of other people that one infected person will infect, in a completely non-immune population.
Different experts have estimated the R0 of the Wuhan coronavirus is anywhere from 1.4 to over five, however the World Health Organisation believes the RO is between 1.4 and 2.5.
Here’s how a virus with a R0 of two spreads:
Authors: C Raina MacIntyre, Professor of Global Biosecurity, NHMRC Principal Research Fellow, Head, Biosecurity Program, UNSW