EpidemicsR0: How Scientists Quantify the Intensity of an Outbreak Like Coronavirus and Its Pandemic Potential
“R0,” pronounced “R naught,” represents an important concept in epidemiology and is a crucial part of public health planning during an outbreak, like the current coronavirus pandemic that’s spread globally since it was first identified in China. Scientists use R0 – the reproduction number – to describe the intensity of an infectious disease outbreak. R0 estimates have been an important part of characterizing pandemics or large publicized outbreaks, including the 2003 SARS pandemic, the 2009 H1N1 influenza pandemic, and the 2014 Ebola epidemic in West Africa. It’s something epidemiologists are racing to nail down about SARS-CoV-2, the virus that causes COVID-19.
If you saw the 2011 movie “Contagion,” about a worldwide pandemic of a new virus, then you’ve heard the term “R0.”
Pronounced “R naught,” this isn’t just jargon made up in Hollywood. It represents an important concept in epidemiology and is a crucial part of public health planning during an outbreak, like the current coronavirus pandemic that’s spread globally since it was first identified in China.
Scientists use R0 – the reproduction number – to describe the intensity of an infectious disease outbreak. R0 estimates have been an important part of characterizing pandemics or large publicized outbreaks, including the 2003 SARS pandemic, the 2009 H1N1 influenza pandemic and the 2014 Ebola epidemic in West Africa. It’s something epidemiologists are racing to nail down about SARS-CoV-2, the virus that causes COVID-19.
How Much Will a Disease Spread?
The formal definition of a disease’s R0 is the number of cases, on average, an infected person will cause during their infectious period.
The term is used in two different ways.
The basic reproduction number represents the maximum epidemic potential of a pathogen. It describes what would happen if an infectious person were to enter a fully susceptible community, and therefore is an estimate based on an idealized scenario.
The effective reproduction number depends on the population’s current susceptibility. This measure of transmission potential is likely lower than the basic reproduction number, based on factors like whether some of the people are vaccinated against the disease, or whether some people have immunity due to prior exposure with the pathogen. Therefore, the effective R0 changes over time and is an estimate based on a more realistic situation within the population.
It’s important to realize that both the basic and effective R0 are situation-dependent. It’s affected by the properties of the pathogen, such as how infectious it is. It’s affected by the host population – for instance, how susceptible people are due to nutritional status or other illnesses that may compromise one’s immune system. And it’s affected by the environment, including things like demographics, socioeconomic and climatic factors.
For example, R0 for measles ranges from 12 to 18, depending on factors like population density and life expectancy. This is a large R0, mainly because the measles virus is highly infectious.
