Nearly 80 per cent of the Covid-19 infections have been caused by the top 30 per cent most infectious people worldwide and there is a very wide range of infections that are still undetected, says Dr Lucy Li, a data scientist at the Chan Zuckerberg Biohub (CZB).
While there are still individual super-spreaders, perhaps more important for this current coronavirus pandemic is the contribution of super-spreading events where large numbers of people congregate in close proximity, she said during an interview with an Amazon team this week.
Her latest research to estimate unreported Covid-19 cases is supported by the AWS Diagnostic Development Initiative, a global programme to support organisations working to bring better, more accurate, diagnostics solutions to market faster.
Biohub is a joint collaborative effort by UC Berkeley, University of California, San Francisco (UCSF) and Stanford University funded by a $600 million commitment from Facebook CEO and founder Mark Zuckerberg and his wife Priscilla Chan.
According to Li, one thing that makes Covid-19 challenging to track is that not all individuals who have it exhibit symptoms.
“The virus genome mutates at a fairly constant rate as it spreads across the population, even when it’s spreading in asymptomatic individuals. That means that every time someone new is infected, the virus changes a little bit and that mutation happens at a fairly constant rate as it spreads,” she explained.
So even if we aren’t able to test everyone in the population, as long as we know how quickly the virus mutates, we can infer the likely number of undetected transmission events between people who were tested.
“For this research, I created a mathematical model to estimate the number of undetected infections at 12 locations in Asia, Europe, and the US over the course of the pandemic,” she informed.
She found that there was a very wide range of infections that were undetected across these locations.
The rate of undetected infections was as high as over 90 per cent in Shanghai.
“We also found that there was significant change over time in the probability of detecting a case,” said Li.
When the virus was first transmitted to these 12 locations, over 98 per cent of infections were undetected during those initial couple of weeks, indicating that the epidemic was already taking off by the time that intense testing started happening.
The overall number of global Covid-19 cases has surpassed the 11 million mark, while the deaths have soared to more than 5,24,000, according to Johns Hopkins University.