As the COVID-19 pandemic continues to accelerate globally, Burnet Institute Epidemiologist, Professor Mike Toole AM, gave a video update on key trends, including mutations of the SARS-CoV-2 virus and superspreading events.
“The situation in Europe is worsening many countries are seeing all-time record cases,” Professor Toole said, as new daily cases have surpassed 10,000 in the UK, France and Spain.
Professor Toole’s updated examined upswings in COVID-19 infections in Myanmar, which has seen much higher rates of infection than other countries in the Greater Mekong sub-region.
The analysis, prepared by Burnet’s Know-C19 Hub, also examined mutations in the spike protein of the SARS-CoV-2 virus, which may cause higher transmission and transmissibility in humans, and overdispersion of the COVID-19 (superspreading).
“Mutations are important because therapies like vaccines and drugs typically target proteins specifically… so mutations could compromise those interactions and present a major challenge, particularly for therapeutic drug development,” Professor Toole said.
However, he said significant studies out of Houston, Texas and the UK had shown that the D614G mutation has, so far, not made the virus more clinically virulent, nor has it affected the immune system’s ability to recognise it.
Read the full analysis
Overdispersion of the Virus (Superspreading)
- COVID-19, like other diseases caused by coronaviruses, such as SARS and MERS, tend to cluster rather than spread linearly like influenza. COVID-19 is also subject to large superspreading events where one person may infect dozens or hundreds of others. The metric R0 does not reflect the reality of SARS-CoV-2 transmission.
- The over-dispersion factor k is a better metric to characterise transmission. The lower the value of k the fewer people are causing most spread of the virus. This value has been estimated as 0.12 for SARS and 0.25 for MERS while estimates for COVID-19 are as low as 0.1 meaning that just 10 percent of infected cases are infecting more than 80 percent of people.
- Superspreading events have been associated with large indoor gatherings in poorly ventilated spaces and where people may be singing (choir practices and church services) or speaking loudly (nightclubs and bars). It is likely that in this (indoor) environment an individual with a high viral load in their pharynx has introduced the virus into an environment where it spreads rapidly.
- The concept of over-dispersion has implications for contact tracing. Rather than focusing only on ‘forward’ tracing, namely finding people that have been in contact since the person was infected, there should also be efforts to see who first infected the subject. This may reveal new previously unidentified infected individuals within the cluster.