What Does ‘Eliminating’ Covid-19 Mean, Anyway?
Understanding what elimination, eradication, and extinction mean to epidemiologists
Last Friday, the prestigious medical journal The Lancet published a stunning news headline: “New Zealand eliminates COVID-19.” In the piece, health journalist Sophie Cousins reported that the country had ended “community transmission of SARS-CoV-2” and recorded its first day of no new Covid-19 cases early last week — about a month after it had started its aggressive lockdown.
To the non-technical ear, this description of New Zealand’s very specific milestone may have seemed at odds with the way we usually think about “elimination.” Using the common definition of the word would suggest that the virus was completely wiped out from the island nation.
But the Lancet headline used “elimination” in the epidemiological sense, which means a very different thing, as I’ll explain below. The words “eradication” and “extinction” — which I hope we’ll be seeing in the news soon — are also used by epidemiologists to talk about infectious disease in very specific ways.
The following definitions were put forth by former CDC Deputy Director Dr. Walt Dowdle in a document for the CDC in 1999, though there’s plenty of nuanced scientific debate about how these terms are defined.
Elimination: Eliminating Covid-19 means that the incidence of new cases in a defined geographical region has been reduced to zero as a result of deliberate efforts. Notably, Dowdle writes, “continued intervention measures are required.” More on this later.
Eradication: Eradicating Covid-19 means that the worldwide incidence of Covid-19 infection has been reduced to zero as a result of deliberate efforts. “Intervention measures,” says Dowdle, “are no longer needed.”
Extinction: For Covid-19 to be considered extinct, the SARS-CoV-2 virus would have to cease existing anywhere in nature or in a laboratory.
One reason why defining these terms is so contentious is because of what they mean for public health intervention. David L. Heymann, the WHO’s Assistant Director-General for Health Security and Environment, argued in 2006 that the way Dowdle defined “eradication” was insufficient…