On Friday the U.S. ordered 500,000 additional doses of Jynneos monkeypox vaccine—the safer of two available in the U.S.—already in storage be filled and readied, officials said on a Friday press call. The country currently has 73,000 doses of the vaccine in the strategic national stockpile and another 300,000 will soon arrive, officials said, adding that nearly 16 million doses can be delivered on request of the U.S.

The U.S. has 69 labs capable of testing for monkeypox and is working to expand the network, Dr. Rochelle Walensky, head of the U.S. Centers for Disease Control and Prevention, said on the call.

As of Friday the country had seen 45 cases of monkeypox in 15 states and Washington, D.C. Global cases sat at 1,300 in 31 countries, and no deaths have been reported in the U.S. or elsewhere, officials said.

While monkeypox presents a low risk to the public, community transmission is possible, and “all Americans should get educated about this disease,” including symptoms and how to prevent it, Walensky said.

The disease is known to be transmitted through direct contact, either with bodily fluids and lesions, or materials like bedsheets that have touched such things. However, it may also be transmitted through respiratory secretions “with close, sustained face-to-face contact,” she said, adding that it’s not believed to linger in the air and “not typically transmitted during short periods of shared air.”

Monkeypox is not transmitted “through casual conversation, passing in the grocery store, touching the same doorknob,” she said.

It is not yet known if the virus can be transmitted through semen or vaginal fluids. It’s difficult to tease out, in cases of close contact, if the disease was transmitted through touch, respiratory droplets, or sexual contact, Walensky added.

Symptoms of monkeypox in the current outbreak tend to be “mild, sometimes, only in limited areas of the body,” differing from classic cases, she said. Patients may not experience the typical flu-like symptoms before the rash appears. A typical rash is diffused, often appearing on the face and hands before spreading to other parts of the body. But in some current cases, only one lesion is seen—in the genital area—and it may look more like chickenpox or a sexually transmitted disease like herpes or syphilis—or even a pimple or a blister. It’s also possible to have an STI and monkeypox at the same time, making detection more difficult.

Another unusual symptom seen in recent cases, according to officials: proctitis, or inflammation of the lining of the rectum, which can make defecation, and potentially sexual activity, painful.

As of Friday the U.S. had delivered 1,400 vaccine courses and 100 treatment courses, said Dr. Raj Panjabi, senior director for global health security and biodefense, at the White House.

“Short range” airborne transmission possible

As the virus continues to spread beyond Africa, where it’s endemic, via an atypical pattern, scientists are rushing to figure out just how it’s spreading.

Monkeypox is usually found in rural African areas where people have close contact with infected rats and squirrels. It is typically transmitted from human to human through close contact, which may include sex and could include contact with personal items like sheets and clothing. Airborne transmission is known to be possible but has yet to be confirmed.

Human-to-human transmission of the smallpox-related virus can occur via “respiratory droplets (and possibly short-range aerosols),” the World Health Organization wrote in a June 4 situation update, in which it cautioned against large gatherings, which may promote transmission.

At a Wednesday press briefing, Rosamund Lewis, WHO’s technical lead on monkeypox, said the risk of aerosol transmission is not fully known, but medical personnel caring for monkeypox patients should wear masks.

In terms of disease transmission, “droplets” and “aerosols” are different. Droplets are larger moisture particles that fall quickly to the ground, like drops of saliva expelled when a person coughs. Aerosols are much smaller particles that can linger in the air. If a virus is spread through aerosols, it is considered airborne.

On Monday the U.S. Centers for Disease Control raised its alert level for potential monkeypox transmission among travelers, advising them, among other things, to wear a mask while traveling. On Tuesday the masking advice disappeared from its website. When asked why, the CDC told Fortune it had removed the phrase “because it caused confusion.” The agency did not respond to a request for further elaboration, nor did it respond when asked if there was concern about airborne transmission.

While the CDC’s web page on monkeypox transmission for the general public does not mention potential airborne spread, its guidance for clinicians advises that tasks that could “resuspend dried material from lesions,” such as dusting, sweeping, or vacuuming, should be avoided while patients are hospitalized.

“Intubation and extubation, and any procedures likely to spread oral secretions, should be performed in an airborne infection isolation room,” the page states.

Dr. Georges Benjamin, executive director of the American Public Health Association, told Fortune on Friday regarding the CDC’s reversal on mask guidance: “I don’t know what to do with that.”

Aerosol transmission is possible, he said, but “it’s not going to be like COVID.”

“If I was cleaning a bed and taking care of a patient who had been infected, I’d probably wear gloves and a mask,” he added. “That’s a reasonable protection—a tight-fitting N95 mask.”

He emphasized that cases are mainly, but not exclusively, being seen among men who have sex with men, and that the virus is generally spread via “close contact.”

“But I think the lesson we should learn from COVID is that we know what we know, and we need to make sure we don’t make assumptions about what we don’t know,” he said.