Transmission of monkeypox between people was relatively rare in the past, and the virus normally jumped from animals to humans. But monkeypox is now spreading more efficiently between people. The WHO has said the international community did not invest enough resources in fighting monkeypox in Africa before the global outbreak.

“This transmission has been occurring in African countries in two particular zones over a large number of years, and we don’t fully understand what’s driving transmission in those countries,” said Dr. Mike Ryan, head of the WHO’s health emergencies program, earlier this week. “There’s a lot more investigation to do and a lot more investment to make in understanding that problem.”

Monkeypox is primarily spreading through skin-to-skin contact during sex. Men who have sex with men are at the highest risk right now, as the majority of transmission has occurred in the gay community. However, the WHO and the CDC have emphasized that anyone can catch monkeypox regardless of sexual orientation.

Scientists in Spain and Italy detected monkeypox virus DNA in semen from positive patients, though it’s still unclear whether whether the virus can spread through semen during sex. The Spanish scientists also detected monkeypox DNA in saliva samples.

It’s also unclear whether the virus can spread when people are infected but don’t have symptoms, known as asymptomatic transmission.

Lewis, the WHO’s monkeypox expert, said 99% of cases reported outside Africa are among men and 98% of infections are among men who have sex with men, primarily those who have had multiple, recent anonymous or new sexual partners. The virus has been detected outside the gay community, but transmission has been low so far. The CDC confirmed monkeypox in two children on Friday.

The WHO and CDC have repeatedly warned against stigmatizing gay and bisexual men, while at the same time stressing the importance of communicating the reality of how the virus is currently spreading so people in communities at highest risk can take action to protect their health.

“People want the information to know how to protect themselves, in what circumstances are people perhaps at risk or getting infected,” Lewis said earlier this week. It’s crucial for health agencies and community organizers to broadly disseminate information on how to reduce the risk of infection ahead of major celebrations and festivals this summer, she said.

Tedros warned stigma and discrimination are violations of human rights that will undermine the public health response to the outbreak. He called on national governments to protect individuals’ fundamental rights as they respond to the virus.

“We seek your strong commitment to uphold human dignity, human rights so that we can control this outbreak,” Tedros said.

The U.S. CDC recommends that people avoid intimate physical contact with individuals who have a rash that looks like monkeypox, and consider minimizing sex with multiple or anonymous partners. People should also consider avoiding sex parties or other events where people aren’t wearing a lot of clothing.

Individuals who do decide to have sex with a partner who has monkeypox should follow CDC guidance on lowering their risk, according to the health agency.

In the past, monkeypox normally began with symptoms similar to the flu, including fever, headache, muscle aches, chills, exhaustion and swollen lymph nodes. The disease then progressed into a rash that can spread over the body. Patients are considered most infectious when the rash develops.

But in the current outbreak the symptoms have been atypical. Some people are developing a rash first, while others are showing a rash without any flu-like symptoms at all. Many patients have developed a localized rash on their genitals and anus.

The CDC and WHO have said the rash is easily confused with common sexually transmitted diseases. They have told health care providers that they should not rule out monkeypox simply because a patient tests positive for a sexually transmitted disease.

Although monkeypox can spread through respiratory droplets, that method requires prolonged face-to-face interaction, according to the CDC. Health officials do not believe monkeypox is spreading through small aerosol particles like Covid. Respiratory droplets are heavier so they do not stay airborne for as long, while Covid is an airborne virus, which is one of the reasons it’s so contagious.

Monkeypox can also spread through contact with contaminated materials, such as bedsheets and clothing.

“This disease is transmissible, but it’s not that transmissible. It’s a disease in which transmission can be contained,” Ryan said. “Like we said in Covid, don’t be the person to pass this disease on.”

Because monkeypox is not a new virus, there are already vaccines and antivirals to prevent and treat the disease it causes, though they are in short supply. The U.S. is already distributing tens of thousands of doses of a vaccine called Jynneos in an effort to quash the outbreak. The Food and Drug Administration approved the two-dose vaccine in 2019 for adults ages 18 and older who are at high risk of monkeypox or smallpox infection.

The Biden administration has distributed more than 300,000 Jynneos doses to states and cities since May and another 786,000 doses are being delivered to the U.S. The Health and Human Services Department has ordered another 5 million doses through 2023.

CDC Director Dr. Rochelle Walensky said the demand for monkeypox vaccines is outstripping the available supply in the U.S., which has led to long lines in places such as New York City — an epicenter of the outbreak.

Jynneos is manufactured by Bavarian Nordic, a biotech company based in Denmark. Right, now Bavarian Nordic has up to 5 million doses available for the rest of the world excluding the U.S., a company spokesperson said. But Bavarian Nordic has the capacity to fill 40 million liquid frozen and 8 million freeze dried doses a year, the spokesperson said.

The U.S. also has more than 100 million doses of an older generation smallpox vaccine called ACAM2000, made by Emergent BioSolutions, that is also likely effective at preventing monkeypox. But ACAM2000 can have serious side effects and is not recommended for people who have weak immune systems, including HIV patients, people who have certain skin conditions and pregnant women.

ACAM2000 uses a mild virus strain in the same family as monkeypox and smallpox to confer immunity. But the mild strain used by the vaccine can replicate, which means people who receive ACAM2000 have to take precautions to make sure they do not give the virus to others or spread a rash from the injection site to other parts of their body. The Jynneos vaccine does not have this risk because it does not use a replicating virus strain.

There is no data yet on the effectiveness of the vaccines against monkeypox in the current outbreak, according to the CDC.

The WHO is not recommending mass vaccination at this time, and the U.S. is currently reserving the vaccines in its stockpile for people who have confirmed or presumed monkeypox exposures. Unlike Covid, vaccines against smallpox and monkeypox can be administered after exposure due to the viruses’ long incubation period. But the vaccines need to be administered within four days of exposure for the best chance of preventing onset of the disease, according to the CDC.