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This illustration provided by the Centers for Disease Control and Prevention in January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). This virus was identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China. (Centers for Disease Control and Prevention via AP)

Novel Coronavirus: Understanding the Epidemiology

by Rossi A. Hassad PhD, MPH
February 07, 2020
With twelve confirmed cases of the novel coronavirus (2019-nCoV) in the U.S., there is growing fear and concern, particularly over the virus’s transmission dynamics, even though infection risk in the U.S. remains low.

In order to effectively stem this epidemic, a clear and precise understanding of the transmission dynamics is necessary. Our direct knowledge and understanding of this previously undetected coronavirus is limited, but evolving. Indeed, the accelerated spread of the outbreak, with one recent report estimating that about 76,000 individuals have been infected in China, is of tremendous concern. Adding to this are reports of asymptomatic spread of this novel coronavirus, though in general, transmission from asymptomatic cases is not considered a significant factor in propagating the spread of an epidemic of this nature.

Assuming that asymptomatic spread is occurring in China, and is prevalent, and given the relatively low (crude) case fatality rate of about 2%, this could imply that most of those infected are mild cases. This scenario could prove a blessing in disguise, as in theory, it could hasten the development of herd immunity, when large proportions of the population are immune to a disease through vaccination or recovery from infection. Herd immunity could reduce the severity and duration of the epidemic in China by creating a barrier to further spread of the virus across the community. It could interrupt the chain of transmission and stop or slow the progression of the outbreak. In other words, the virus needs susceptible hosts to propagate the outbreak.

While our knowledge about the incubation period, virulence, contagiousness, and other transmission parameters for novel coronavirus is still lacking, the CDC is taking an evidence-based and multifaceted approach to addressing the outbreak by enhancing our infectious disease surveillance and response systems with education and awareness campaigns, travel screenings and restrictions, as well as isolation and quarantine measures. This approach is also informed by evidence from other coronavirus outbreaks (SARS and MERS).

As has been widely reported, World Health Organization (WHO) declared the outbreak a Public Health Emergency of International Concern (PHEIC), and the U.S. government declared a public health emergency for the entire U.S., authorizing mandatory quarantine among other measures.

However, from a reasoned epidemiological perspective, the risk of infection within the U.S. remains low to zero. In particular, nine of 12 U.S. cases were infected outside of the U.S., and the remaining two cases contracted the virus from a household member who was infected overseas. Other sporadic travel-related cases in the U.S. can be expected, but as already demonstrated, they will quite likely be quickly identified and contained given the comprehensive, effective, and robust infectious disease surveillance and response systems in place throughout the U.S., as well as the CDC’s infection control guidelines.

Additionally, active and substantive research is in progress to develop a vaccine for 2019-nCoV, and this process is being fast-tracked. It is clear that the CDC and other agencies are working optimally to keep America safe, and this should be reassuring to all.

Rossi A. Hassad, PhD, MPH, is an epidemiologist and professor at Mercy College, in Dobbs Ferry, New York. He is a member of the American College of Epidemiology and a fellow and chartered statistician of Britain’s Royal Statistical Society.

LAST UPDATED 02.10.2020
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