Monkeypox, a potentially lethal disease responsible for an alarming rise in cases in North America and Europe over the past three weeks, is primarily spreading through sex between men, according to the World Health Organization.

The disease is spread through close contact with infected people, animals, or materials that are contaminated with the virus. It enters the body through broken skin, the respiratory tract or through the eyes, nose or mouth, according to the CDC.

The virus is not considered a sexually transmitted infection, or spread through semen and vaginal fluids, WHO officials noted. Anyone in close contact with a person who has the virus is considered at high risk of infection, however.

“Many diseases can be spread through sexual contact. You could get a cough or a cold through sexual contact, but it doesn’t mean that it’s a sexually transmitted disease,” Andy Seale, an adviser to the WHO about HIV, hepatitis and other sexually transmitted infections, told CNBC.

In response to the rising number of monkeypox cases worldwide, Bavarian Nordic, a Danish vaccine manufacturer, is ramping up production of its smallpox vaccine to help governments fight the growing outbreak, according to a Wall Street Journal report.

As of May 21, 92 confirmed cases and 28 suspected cases of monkeypox have been reported to the WHO from 12 countries, including the U.S., Australia, Germany, and Spain.

In the U.S., Centers for Disease Control and Prevention officials told Fortune last week that health officials are monitoring six people for suspected cases of monkeypox, all of whom sat next to a person on a May 3-4 flight from Nigeria to London who eventually developed the virus.

Monkeypox is a rare disease related to smallpox and cowpox that causes fever, muscle aches, and lesions. The incubation period, or time between exposure and the onset of symptoms, is usually a week or two but can range from five to 21 days, according to the CDC.

In Africa, where the disease is typically found, monkeypox has proven deadly in as many as 10% of infected persons, the CDC notes. The illness typically lasts anywhere between two and four weeks.

While there is no vaccine that specifically targets monkeypox, smallpox vaccines including the one offered by Bavarian Nordic, can protect against monkeypox infections by at least 85%, according to the CDC.

Known as Jynneos in the U.S., the Bavarian Nordic smallpox vaccine is one of two vaccines currently licensed in the U.S. to prevent smallpox, according to the CDC. It is the only vaccine that the U.S. specifically licenses to prevent monkeypox, however.

Speaking to the Wall Street Journal, Bavarian Nordic CEO Paul Chaplin said the company has received calls from “dozens of countries” in recent weeks asking about Jynneos, which is known as Imvanex in Europe and Imvamune in Canada.

Supply of the vaccine is currently limited, but the company will be increasing its manufacturing in the weeks and months ahead, Chaplin told the Wall Street Journal.

“We feel confident based on discussions that we’ll be able to meet the demand in a relatively short period of time,” Chaplin said.

Speaking to reporters on May 22, President Joe Biden said the public should be concerned about the rising number of cases in the U.S. and abroad.

“They haven’t told me the level of exposure yet, but it is something that everybody should be concerned about,” Biden told reporters. “It is a concern in that if it were to spread, it would be consequential.”

On May 23, Biden backtracked those comments, saying the country has “vaccines to take care of it.”

"I just don't think it rises to the level of the kind of concern that existed with COVID-19,” Biden said.

According to Chaplin, the U.S. and Canada are the only two countries that have meaningful stockpiles of the Bavarian Nordic vaccines. The CDC says the U.S. has access to enough doses of smallpox vaccine to vaccinate every person in the United States if an outbreak were to occur.