Indian police personnel wear facemasks as a preventive measure against the spread of the COVID-19 coronavirus outbreak, outside a hotel in Amritsar on March 6, 2020.

Earlier in the outbreak, U.S. health officials said there was a hypothesis among mathematical modelers that the outbreak "could potentially be seasonal" and relent in warmer conditions.

"We have to assume that the virus will continue to have the capacity to spread," Dr. Mike Ryan, executive director of WHO's health emergencies program, said at the agency's headquarters in Geneva. "It's a false hope to say, yes, that it will disappear like the flu." "We hope it does. That would be a godsend," he added. "But we can't make that assumption. And there is no evidence."

World leaders should not assume COVID-19 will be seasonal and subside in the summer, like the flu, the World Health Organization said Friday.

"Other viral respiratory diseases are seasonal, including influenza and therefore in many viral respiratory diseases we do see a decrease in disease in spring and summer," Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said on a Feb. 25 conference call. "And so we can certainly be optimistic that this disease will follow suit."

Earlier Friday, the total number of COVID-19 cases surpassed 100,000 worldwide. The majority of the cases are in mainland China, followed by South Korea, Iran and Italy. In the United States, 233 cases have been confirmed, including 14 deaths, according to John Hopkins University.

During a press briefing Monday, WHO officials said they don't know how COVID-19 behaves, saying it's not like influenza. They added that while much is known about the seasonal flu, such as how it's transmitted and what treatments work to suppress the disease, that same information is still in question when it comes to the coronavirus.

"This is a unique virus, with unique features. This virus is not influenza," WHO Director-General Tedros Adhanom Ghebreyesus said. "We are in uncharted territory."

World health officials say are "deeply concerned" about the increasing number of countries reporting cases, especially those with weaker health-care systems.

Tedros said Friday that health officials are also concerned about hospitals, which have been running very "lean and mean."

"When I say lean and mean, making it very close to what they need during normal times the number of beds they need and so on," he said. "And that's why we see some surprise in high-income countries and when emergencies actually arrive, triggering or expanding that lean and mean system becomes a bit difficult and at times taxing."

He said that may force some countries to discharge patients early because the system "is adapted to lean and mean approach."

"OK, running hospitals in a lean and mean fashion could be OK during regular times, but how can we expand the capacity in a few hours when the need comes?" he said. "It's not COVID only by the way. It could be an earthquake, or it could be a tsunami or another disaster, whether it's man-made or natural."