The United States has stockpiled millions of doses of two smallpox vaccines, also effective against monkeypox. But the outbreaks so far are clustered in other countries.
As more than a dozen countries grapple with outbreaks of monkeypox, health officials worldwide are rushing to assess reserves of vaccines and treatments that may be needed to contain the spread.
The U.S. emergency stockpile holds two vaccines approved by the Food and Drug Administration that could be used to contain monkeypox, officials at the Centers for Disease Control and Prevention told reporters on Monday.
The stockpile contains more than 100 million doses of the original smallpox vaccine. But that vaccine is associated with side effects and shouldn’t be given to certain patients, including those who are immuno-compromised.
A newer vaccine, called Jynneos, was approved in 2019 for prevention of both smallpox and monkeypox. More than 1,000 doses are held in the stockpile, Dr. Jennifer McQuiston, a deputy director at the C.D.C., said.
“We expect that level to ramp up very quickly in the coming weeks, as the company provides more doses to us,” she said. Doses have already been requested from the stockpile for inoculation of some high-risk contacts, she added.
Still, the dimensions of the problem in the United States are not yet clear. As of Monday, officials had confirmed just one case, in Massachusetts, and were evaluating four other patients.
The situation overseas is more concerning. As of Monday, there were more than 100 confirmed cases in 14 countries outside Africa, and dozens more under investigation. That day, the European Center for Disease Prevention and Control urged health officials in Europe to assess the availability of smallpox vaccines, antivirals and personal protective equipment.
The World Health Organization is holding stockpiles of about 31 million smallpox vaccine doses, but they may have lost some potency in the decades since they were made.
The largest monkeypox clusters have been reported in Europe, particularly in Spain, prompting some experts to hypothesize that the outbreaks originated in that country. Spanish officials are investigating two potential sources: a Gay Pride event held in the Canary Islands beginning on May 5 that drew about 80,000 revelers, as well as a sauna in Madrid.
Although many of the initial infections in Europe were reported among men who have sex with men, other segments of the population are clearly vulnerable. Officials “must keep a broad definition, so as not to leave out other groups which may emerge as being important,” said Dr. Boghuma Titanji, an infectious diseases physician at Emory University in Atlanta.
Britain reported its first cases of monkeypox in patients with no known links to West Africa just over a week after the event in the Canary Islands. But some experts said the pattern of infections suggested that the virus might have been circulating outside Africa for several months.
The monkeypox virus is endemic to West and Central Africa, and continuing community transmission elsewhere is highly unusual. “We do not usually see this level of apparently sustained spread in outbreaks occurring outside of endemic regions and not associated to travel or animal exposure,” Dr. Titanji said.
President Biden warned on Sunday that “everybody should be concerned,” but added the next day that the United States had enough doses of vaccine to protect Americans. In any event, mass immunization campaigns are unlikely in any country, including the United States, several experts said. And the outbreaks are unlikely to warrant such a campaign.
Instead, officials may recommend immunizing a circle of close contacts around those found to be infected — an approach called ring vaccination that has been used to suppress other outbreaks of rare diseases.
Mass immunization campaigns are not recommended because the older smallpox vaccine can have rare but severe side effects, such as inflammation of the heart muscle. That vaccine also may be risky for immuno-suppressed people, including those with undetected H.I.V. infection. It can be fatal even in people with eczema, which affects an estimated 30 percent of Americans.
After the Sept. 11 attacks, the United States considered immunizing the entire population to protect against a terrorist attack using smallpox. “In the end, it was decided no, because of the negative consequences of vaccinating lots of people,” Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.
“Vaccine side effects are rare,” he added. “But once you start giving it to millions of people, then they will start to add up.”
Newer generation vaccines like Jynneos are likely to be safer for large groups, and ring vaccination may be enough to contain the virus. “Hopefully, presumably, monkeypox is still relatively rare right now, and a ring vaccination strategy may well be able to keep it completely at bay,” Dr. Hanage said.
In addition to vaccines for prevention, the United States has procured more than two million doses of an antiviral pill called tecovirimat, which is approved to treat smallpox in those who become infected, according to the C.D.C. The agency is also working with the drug’s manufacturer to develop an intravenous form.
Human monkeypox was first identified in 1970 in a 9-year-old boy in a region of the Democratic Republic of Congo where smallpox had been eliminated. Monkeypox cases in the country have significantly increased in the decades since smallpox mass vaccination ended.
In 2003, the United States recorded dozens of monkeypox cases that were traced to infected pets. Although the virus was first discovered in 1958 in monkeys kept for research purposes, it is spread by rodents.
A week to two weeks after exposure, infected people may begin to experience fever, sore throat, cough, fatigue and body aches. They also develop a distinct rash, first on the face, then on the palms of the hand and soles of the feet, and then all over the body. The lesions blister, grow and fill with a white puslike substance.
The pustules, reminiscent of smallpox’s most distinguishing feature, last for about a week before they scab over and heal. Monkeypox patients may also have swollen lymph nodes in the neck, the armpit and the groin.
In some cases, the rash may not be visible because it may be limited to the genital area. The virus can still spread through physical contact or contaminated bed linens, clothes or other materials.
What to Know About the Monkeypox Virus
What is monkeypox? Monkeypox is a virus endemic in parts of Central and West Africa. It is a more benign version of smallpox. It was discovered in 1958, after outbreaks occurred in monkeys kept for research, according to the Centers for Disease Control and Prevention.
Infected people should remain isolated at home and abstain from sexual activity until their scabs dry and fall off. “These are basic strategies that we use in responding to outbreaks all around the world, and they work,” Dr. McQuiston, the C.D.C. official, said.
Infected people should also avoid close contact with immuno-suppressed people, pregnant women and children, all of whom are at high risk of complications if they acquire the virus. Health officials in Belgium are now asking close contacts of infected people to quarantine.
“It’s another reason why if you’re a person who may be at risk due to a weakened immune system to be particularly careful about seeking out early care and evaluation,” Dr. John Brooks, a medical epidemiologist at the C.D.C., said.
On Monday, the European Center for Disease Prevention and Control also cautioned infected people against close contact with pets — and not just because of the animals’ health.
“If human-to-animal transmission occurs, and the virus spreads in an animal population, there is a risk that the disease could become endemic in Europe,” the agency warned.
Some experts have feared for years that there might be a resurgence of monkeypox.
The last known cases of smallpox occurred in 1977, and it was declared eradicated in 1980. With the end of immunization programs for smallpox, the number of people who are susceptible to this family of viruses has risen each year.
Scientists in Portugal sequenced the monkeypox virus in skin lesion samples collected from a male patient on May 4, but that sequence is incomplete. So far, the current strain appears to be closely related to versions exported from Nigeria to Britain, Israel and Singapore in 2018 and 2019, researchers have concluded.
The United States sequenced a sample from the first confirmed case, in Massachusetts, within 48 hours and has shared the sequence publicly. The samples from Massachusetts and Portugal seem closely related, Dr. McQuiston said.
“All signs point to this being an outbreak associated with person-to-person spread,” she added.
The West African version of the virus is thought to cause milder symptoms. It does not spread easily among people and has a fatality rate of about 4 percent, compared with a mortality rate of about 11 percent with the Central African version and 30 percent for smallpox. No deaths have been reported in the current outbreaks.
There is no indication that the virus has changed significantly in virulence or mode of transmission. Unlike the rapidly mutating RNA-based coronavirus, monkeypox is a large DNA virus that is capable of correcting its genetic errors.
“These are particularly stable viruses, so monkeypox is less prone to mutations,” said Dr. Raina MacIntyre, an epidemiologist at the University of New South Wales in Sydney, Australia, and a member of the W.H.O.’s working group on monkeypox.
“I’d be very surprised and very puzzled if there was some dramatic mutation that makes it much more transmissible,” she said.
And this is not the coronavirus. “There really isn’t at this point any mass population risk,” she added. “The virus, as far as we know, is still not very contagious.”