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February 11, 2020

Preparation for Possible Sustained Transmission of 2019 Novel Coronavirus: Lessons From Previous Epidemics

Author Affiliations
  • 1Pfizer Vaccines, Collegeville, Pennsylvania
  • 2Center for Observational and Real-World Evidence, Merck and Co Inc, Kenilworth, New Jersey
JAMA. Published online February 11, 2020. doi:10.1001/jama.2020.1960

Transmissibility and severity are the 2 most critical factors that determine the effect of an epidemic. Neither the 2009 pandemic influenza A(H1N1) virus ([H1N1]pdm09) pandemic or the severe acute respiratory syndrome coronavirus (SARS-CoV) or the Middle East respiratory syndrome coronavirus (MERS-CoV) epidemics had the combination of both high transmissibility and severity. Control strategies are driven by this combination. R0, the basic reproduction number, is a commonly used measure of transmissibility and is defined as the number of additional persons one case infects over the course of their illness. An R0 of less than 1 indicates the infection will die out “eventually.” An R0 of greater than 1 indicates the infection has the potential for sustained transmission.

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    1 Comment for this article
    Understanding R and Disease Control
    Oz Mansoor | Public Health Physician, Wellington
    The message, that we need to prepare for a pandemic is vital. But the article misreports some key ideas. Firstly, SARS was not controlled "because a high proportion of cases were severe." While that helped , it was because cases were not infectious before some days after symptom onset (usually in the second week of illness). This gave more time for case identification and isolation. And most cases did not pass on infection to anybody, but a few spread to many. When all such individuals were identified and isolated, spread stopped.

    Unfortunately, the new virus
    appears to be spreading from people much earlier in the course of illness, and even with mild symptoms - which was never documented for SARS. However, it is not clear that it is any different or better at spread between people, and perhaps with the same pattern of most cases not causing further spread.

    Secondly, the R0, the basic reproduction number, is correctly described as the average number of infections each case causes. But it lacks two key ideas: 1) the 0 after the R implies the native state, which is a fully susceptible population and without any control measures. R is the effectiive number and can include the impact of control measures.

    To claim that it was the lack of transmissibility, rather than the control measures that ended SARS, is not based on any evidence. And it ignores the heroic efforts of affected countries.

    Elimination of SARS demonstrated the potential of globally coordinated collective action, as well as the damage caused by ignorance and prejudice. Most seem to have already forgotten the lessons of SARS.
    CONFLICT OF INTEREST: Worked for WHO/WPRO in SARS response