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COVID-19: What is R0 And What Does It Tell About A Pandemic?

Updates on COVID-19 is 24/7 on the internet. If you have been reading coronavirus news all the time, you might have come across the word R0, pronounced as R-naught.

R0 is a epidemiologic metric that calculate the contagious property of a new disease. It gives information about how fast the virus can spread from one person to other. Take a look at its details.

What Is R0 Number?

R0 or R-naught is referred to as a reproductive number. During an outbreak of a pandemic, scientists and medical researchers calculate a crucial metric that denotes the contagious nature of an infection. This metric is known as R0.

R-naught denotes an average number of people who may get infected from an already sick person. The matric is applied to a population who were free of infection before and has no immunity against the virus. This number helps experts to find out how fast a disease can spread and how to contain it. Also, it says whether the spread of the disease is increasing, constant or going down day by day.

For example, if a disease has an R0 of 10, it means that one sick person can transmit the virus to 10 more people, considering that they are not vaccinated or have no previous immune to the infection.[1]

Values Of R0

R0 value is applied when there's no previous vaccination for the disease, no one has got it before and no method has been developed yet to control its spread. Also, the value of R0 is not fixed as it may get decreased by the introduction of effective preventive measures.

There are three values of R0: less than one, equal to one and more than one.

  • When R0 is less than one, every sick person can cause less than one new infection. Chances are that the disease rate may certainly decline or completely vanish.
  • When R0 is equal to one, every sick person can cause one new infection. This is a moderate condition as the disease will stay stable but won't become an epidemic.
  • When RO is more than one, every sick person can cause more than one new infection. It is a critical condition as the infection may spread and cause an outbreak of an epidemic.

How R0 Is Calculated?

R0 is calculated based on three factors: contact rate, infectious period and mode of transmission of the disease.

  • Contact rate: It says about the number of individuals who had close contact with the sick person. If the contact rate is decreased by imposing self-quarantine or lockdowns, the R0 is surely going to decrease.
  • Infectious period: It refers to the time period a sick person carries the infection in their body. It also depends on the age as children tend to carry viruses for longer periods compared to adults.
  • Mode of transmission: It refers to the mode of contact with the sick person. If the mode of transmission is air (such as flu), the virus tends to spread quickly compared to transmission via bodily fluids as in HIV.

What Is The R0 Of COVID-19?

There were many outbreaks of diseases in the past. The mortality rate of people during that time was high as medical science was not advanced as today. But as time passed by, the mortality rate decreased due to the invention of vaccines and several effective drugs against the disease.

If we look into the history of diseases, the 1918 outbreak of Spanish flu is estimated to have an R0 of 1.8 which was responsible for around 50 million deaths worldwide. SARS (2003) has an R0 of 2-5 and measles with R0 value as 12-18. According to a study published in the New England Journal Of Medicine, the R0 of COVID-19 is estimated to be 2.2 [2]

From the above metric, it is clear that one COVID-19 positive person can spread the infection to more than two people, which is critical. This is the reason why lockdowns have been imposed to prevent the further spread of the virus. The metric also shows that COVID-19 is less contagious than SARS of 2003 and far less than measles.

Prevention Tips

  • Maintain hand hygiene.
  • Wear a mask before visiting crowded places.
  • Check for symptoms and contact medical care if you doubt of catching the infection.
  • Maintain a clean environment at home.
  • Don't touch eyes, nose and mouth with contaminated hands.
  • Stay away from social gatherings and stay at home.
  • Avoid eating raw or undercooked meats.
Story first published: Thursday, April 9, 2020, 18:15 [IST]
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