The COVID-19 Coronavirus Disease May Be Twice As Contagious As We Thought
April 7, 2020 / Tara Haelle, Senior Contributor
A single person with COVID-19 may be more likely to infect up to 5 or 6 other people, rather than 2 or 3, suggests a new study of Chinese data from the CDC. It’s not clear if this higher number applies only to the cases in China or if it will be similar in other countries.
If the higher number does remain true elsewhere, it means that more people in a population need to be immune from the disease—either from having already had it or from a vaccine—to stop it from circulating.
The new study, published in the Emerging Infectious Diseases journal, shifts the R0 for COVID-19 from about 2.2 to about 5.7. With the lower number, only 55% of a population needs to be immune from COVID-19 to stop its spread through herd immunity. Herd immunity refers to enough of a population being immune to a disease that the disease cannot travel through it.
But if more people get infected from a single person with COVID-19, then more people need to be protected from the disease to stop it from continuing to spread. With an R0 of 5.7, approximately 82% of the population needs to be immune to reach herd immunity and stop the disease from spreading easily through the population, the researchers concluded.
The new calculations also estimate the incubation period—the time from being exposed to the virus and developing symptoms—to be an average of 4.2 days, which is in line with most other estimates (though symptoms can still take up to 14 days to show up).
