Experts have been rushing to assess the spread of the Covid-19 virus, which has so far killed more than 19,000 people - mostly in Italy.
Scientists believe Covid-19 has mutated into two strains: the older ‘S-type’ appears to be milder and less infectious, while the ‘L-type’ which emerged later, spreads quickly and currently accounts for around 70 per cent of cases. It may also be possible to be infected with both types.
In January, the World Health Organisation (WHO) estimated the current trend of the spread, analysing how many people would be infected per case.
According to early WHO estimates, the average reproductive rate (r0) of coronavirus ranged between 1.4 and 2.5. That meant, on average, each confirmed case of coronavirus would infect between 1.4 and 2.5 other people.
Any disease with an r0 of more than one will spread and need effective control measures. WHO said control measures would need to block at least 60 per cent of transmissions to be effective in keeping the coronavirus in check.
The r0 measure is an average - meaning 'super spreaders' could infect many more, and others could infect no other people. Early estimates are also dynamic and could vary significantly as the disease develops.
Risk factors including age and location are also significant variables.
But measured against other viral outbreaks and common diseases, coronavirus appears at the first estimate to be less contagious or deadly than many others, giving hope for containment.
With a mortality rate currently estimated at around 3.4 per cent according to the latest WHO estimates, it is less deadly to those who become affected than Ebola, Sars or Mers.
It is more contagious than some of the most deadly airborne viruses, however. Mers has an r0 of between 0.3 and 0.8, and a fatality rate of around 35 per cent.
At the other end of the scale, chicken pox is very contagious, with each case on average infecting between 10 and 12 others, but with an extremely low fatality rate.
Initial estimates are already being contested. A study from the MRC centre at Imperial College London estimated that, up until January 18, the r0 for coronavirus was between 1.5 and 3.5, higher than the WHO estimate.
That would match it more closely with Sars, which infects on average two to five people per confirmed case.