(CNN)The Wuhan coronavirus outbreak is not a pandemic, World Health Organization officials said Tuesday, adding that they're hopeful transmission of the virus can be contained.
The agency acknowledges that it is challenging to contain the virus because of global mass movement.
"We are not in a pandemic," Dr. Sylvie Briand, director of the World Health Organization's Infectious Hazards Management Department said in a press conference on Tuesday, explaining that the virus is currently considered to be an epidemic with multiple locations.
"We will try to extinguish the transmission in each of these," she said, adding that the agency believes this "can be done with containment measures currently in place."
Current control measures in place include early case detection, early isolation and treatment of cases, contact tracing and social detention measures in places where there is risk of transmission, Briand said. These are the core elements of any outbreak response and might be enough to stop an infection from spreading.
The Wuhan coronavirus is spreading 02:15
A pandemic is define as the worldwide spread of a new disease, but it's not quite as simple as that. The finer details are debated as many factors, including population immunity and disease severity, need to be taken into account.
An epidemic is more than a normal number cases of an illness, specific health-related behavior or other health-related events in a community or region. A disease outbreak is the occurrence of disease cases in excess of what's normally expected, according to WHO.
The last pandemic reported was the H1N1 flu pandemic in 2009, which killed hundreds of thousand worldwide.
WHO last week declared the novel coronavirus outbreak to be a public health emergency of international concern, which it calls "an extraordinary event" that constitutes a "public health risk to other States through the international spread of disease" and "to potentially require a coordinated international response."
Previous emergencies have included Ebola, Zika and H1N1.
The new virus has infected more than 20,000 people across 26 countries and territories and killed more than 420, but the majority of cases -- currently an estimated 78% -- are coming from Hubei province in China, Briand explained.
"This is the epicentre of the outbreak," she said during Tuesday's press conference.
Briand described cases outside of Hubei as "spillover cases" -- people who were mostly infected in Hubei before there was a lockdown there and moved to other places with the disease, causing clusters of cases in other regions. The same can be said of the cases reported in other countries.
Briand believes that in Hubei and places that have spillover, "we can stop transmission," which will prevent the situation from becoming a pandemic.
Many experts believe we've not yet reached pandemic levels, due to the current spread of the outbreak but also because we don't yet know enough about the coronavirus.
"The virus has traveled across multiple continents, but these instances of long-range travel seem to have only resulted in very focal outbreaks," Paul Digard, chair of virology of The Roslin Institute at University of Edinburgh, said in an email. "Unless/until it has been shown to have set up widespread onward transmission chains in other countries, I think it's reasonable to remain calling it an outbreak."
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A pandemic "typically refers to sustained transmission of a new infectious disease across numerous countries," added Dr. Michael Head, senior research fellow in global health at University of Southampton. "Here, we have the coronavirus that has been imported into numerous countries, and we have seen some very limited amount of human transmission outside of China, but not really enough yet for the World Health Organisation to declare a pandemic."
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease in the United States, believes we could be heading toward a pandemic.
"My bottom line is the way this is continuing to evolve every day, it looks like it's heading towards what we would call a pandemic," Fauci said.
But Fauci also said the term itself comes down to semantics -- it "means different things to different people," and that we're in a "gray zone."
