This is the view of researcher Dan Baumgardt from the Department of Physiology, Pharmacology, and Neuroscience at the University of Bristol (UK).
He recalled that when the COVID pandemic erupted, many people revisited the prophetic film “Contagion” (2011). This critically acclaimed movie, known for its scientific accuracy, not only intrigued viewers but also provided valuable lessons.
For instance, when Kate Winslet’s character discussed the impact of various pathogens, she explained how they can spread through our hands to countless objects we touch daily: door handles, drinking fountains, elevator buttons, and more. These objects, known as fomites, are silent carriers of infections.
She also mentioned that each infection is assigned an R0 (or R-naught) value, which indicates how many other people an infected person can potentially infect.
For example, an R0 of 2 means that each infected patient will infect two more people. Those two will, in turn, infect four others. This is how an outbreak develops.
Thus, R0 illustrates how an infection will spread through the human population. An R0 value of 1 indicates that the infection rate will remain stable, while a value below one suggests that the disease will gradually fade away.
This introduction is not random. It helped Dan Baumgardt explain more clearly the rapid spread of the most contagious diseases on the planet.
Measles – The Most Contagious
In recent years, measles has made a comeback worldwide, even in high-income countries like the UK and the USA. This trend is driven by several factors, but the primary reason for the spread of measles is the low rate of among children.
The R0 for measles ranges from 12 to 18. At the highest value of 18, just two cycles of virus transmission from the first infected person can lead to 324 infections. That number is staggering. Fortunately, the protective power of vaccination helps reduce the actual spread of the virus.
Therefore, measles is extremely contagious. It spreads through respiratory droplets released when an infected person coughs or sneezes. Direct contact is not even necessary for infection. An unvaccinated person can contract measles simply by entering a room where an infected individual was present two hours earlier.
What Other Diseases Are on the List?
Other infectious diseases with high R0 values include whooping cough (ranging from 12 to 17), chickenpox (from 10 to 12), and COVID, which varies by subtype but typically has an R0 between 8 and 12. While many patients fully recover from these diseases, the side effects can be quite severe.
Interestingly, a lower level of contagiousness does not mean that a disease is less dangerous, as reported by Science Alert.
Take tuberculosis, for example, which has an R0 ranging from one to four. This value depends on local factors such as living conditions and the quality of available medical care.
The real danger of tuberculosis lies in the difficulty of treating it. If medical measures are not properly taken, the infection can spread beyond the lungs to other parts of the body, including the brain, bones, liver, and joints.
Other with lower contagiousness include Ebola fever, which is deadly. It spreads through close physical contact involving bodily fluids. The R0 for this disease ranges from 1.5 to 2.5.
Among diseases with the lowest R0 values (below one) are Middle East Respiratory Syndrome (MERS), avian influenza, and leprosy. While these infections are less contagious, their severity and potential complications should not be underestimated.
Thus, the threat of any infectious disease depends not only on how it affects the body but also on how easily it spreads.
This brings us to the critically important concept of herd immunity. By strengthening within the population, we can better protect individuals from infection, especially the most vulnerable.
Photo: openverse
