R naught (R0)


R naught (R0) is a mathematical term that indicates how contagious an infectious disease is. 



It’s also referred to as the reproduction number, as an infection is transmitted to new people, it reproduces itself.



R0 tells you the average number of people who will contract a contagious disease from one person with that disease. It specifically applies to a population of people who were previously free of infection and haven’t been vaccinated.



An R0 of 15,in a person who has the disease will transmit it to an average of 15other people. 



That replication continues until been vaccination against the disease or is others are immune to it in their community.


R0 functions as a measure of contagiousness, so low R0 values are associated with lower herd immunity thresholds (HITs), whereas higher R0s result in higher HITs.



R0 value implications: Three possibilities exist for the potential transmission or decline of a disease, depending on its R0 value.



If R0 is less than 1, each existing infection causes less than one new infection: the disease will decline and eventually die out.



If R0 equals 1, each existing infection causes one new infection: disease will stay alive and stable, but there won’t be an outbreak or an epidemic.



If R0 is more than 1, each existing infection causes more than one new infection: transmission of disease  between people, and there may be an outbreak or epidemic.



A R0 value can be applied when everyone in a population is completely vulnerable to the disease. 



No one has been vaccinated



No one has had the disease before.



No way to control the spread of the disease.



In 1918 there was a worldwide outbreak of the swine flu that killed 50 million people: the R0 value of the 1918 pandemic was estimated to be between 1.4 and 2.8.



The swine flu, or H1N1 virus, came back in 2009, its R0 value was between 1.4 and 1.6: vaccines and antiviral drugs made the 2009 outbreak much less deadly.



The R0 for COVID-19 is a median of 5.7, according to a study, about double an earlier R0 estimate of 2.2 to 2.7



With an R0 of 5.7, at least 82 percent of the population needs to be immune to COVID-19 to stop its transmission through vaccination and herd immunity.


Contact investigations for Covid-19 confirm community transmission rates consistent with droplet and contact spread with household attack rates of 10%, healthcare and community attack rates of less than 1% and R0, or average number of new infections caused by infected individual during their  infection of 2-3.


The above is in contrast to airborne viral pathogens such as varicella zoster virus or measles with a attack household rate of 85-90% and R0 zero of 10-18.



R0 of a disease calculate:



Infectious period:



Adults with the flu are typically contagious for up to 8 days, and  children  for longer than that.



A long period of infectiousness will contribute to a higher R0 value.



Contact rate



A high contact rate will contribute to a higher R0 value.



Mode of transmission



The diseases transmitted the fastest and easiest are the ones that can travel through the air, such as the flu or measles.



Diseases that are transmitted through bodily fluids, such as Ebola or HIV, aren’t as easy to contract or transmit. 



Airborne illnesses tend to have a higher R0 value than those spread through direct contact.




Leave a Reply

Your email address will not be published. Required fields are marked *