The Centers for Disease Control and Prevention has identified 21 cases of monkeypox in 11 states, and the numbers are expected to rise, officials said Friday.
Genetic analysis has revealed that while most cases appear to be closely related to the outbreak in Europe, two patients have versions of the virus that appear to have evolved from a case of monkeypox identified in Texas last year.
Of 17 patients for whom the agency has detailed information, all but one were men who have sex with men; 14 had traveled to other countries in the three weeks before symptoms began. Three patients were immunocompromised.
CDC researchers have not been able to identify how a patient in an unidentified state acquired the virus. That suggests there is ongoing community transmission in at least that state and possibly others, Dr. Jennifer McQuiston of the CDC told reporters.
“We really want to increase our surveillance efforts,” he said.
Health officials have identified a total of around 400 contacts of 13 patients who are also at risk of being infected with monkeypox. Identifying at-risk contacts will help officials determine what resources are needed to contain the outbreak.
So far, health officials have delivered about 1,200 vaccine doses and 100 treatments in eight states, according to Dr. Raj Panjabi, senior director for biodefense and global health security at the White House.
The number of monkeypox victims worldwide rose sharply this week, to almost 800 cases as of Friday. The spread of the virus to at least 31 countries outside of Africa, where it is endemic, has raised alarm among scientists and public health officials.
Health officials in some countries are asking anyone who tests positive for monkeypox to self-isolate at home. Britain, which has recorded the most cases, has urged patients to refrain from sex until symptoms subside, to use condoms for eight weeks after that, and to limit interactions with pets and other animals, which can become infected.
As the outbreak spreads, health officials around the world are rushing to collect vaccines and treatments to protect infected people and their close contacts. Options are severely limited.
The United States is one of the few countries that has stockpiled millions of doses of smallpox vaccines and drugs as a precaution against its return. Monkeypox is closely related to smallpox, and vaccines and drugs are expected to be just as effective.
In theory, there are at least two drugs and two types of vaccines available to combat a monkeypox outbreak, but most of these have been tested primarily on animals.
In a recent study of the two drugs in seven patients, only one seemed to offer any benefit, while the other produced toxic side effects.
The older of the two vaccine options was used to eradicate smallpox and can cause severe side effects, including heart problems and death. Most doses have been in storage for decades and may have lost their effectiveness.
The second vaccine option, made by the Danish company Bavarian Nordic, was approved by the Food and Drug Administration in 2019 to prevent smallpox and monkeypox. Called Jynneos in the United States, it’s safer than previous vaccines, but supplies are even more limited.
Several countries, including Canada, Britain and France, have already started vaccinating close contacts of infected people, and many others have placed orders with Bavarian Nordic for additional supplies.
Several experts pointed out that African countries that have battled monkeypox for years have had little or no access to these vaccines and treatments. So far this year, there have been 44 cases in Nigeria and six other African countries where the virus is endemic, but those numbers are likely underestimates.
The monkeypox outbreak in Western countries may further limit access to vaccines and treatments in poor countries, some experts fear. “Vaccines and treatments that are stored elsewhere are not necessarily shared,” said Dr. Ifedayo Adetifa, director of the Nigerian Center for Disease Control.
In Switzerland, the World Health Organization keeps about 2.4 million doses of the vaccine used to eradicate smallpox, and has stored another 31 million doses in five donor countries that could be distributed to countries in need.
But the WHO had previously recommended the vaccine only for people at high risk of exposure, said Tarik Jašarević, a spokesman for the organization. Experts convened by the WHO were scheduled to review the guidance in October, but “that timeline will need to be accelerated,” he said.
The WHO is also evaluating prequalification of the newer Jynneos vaccine, a necessary step for its use in many countries.
CDC scientific advisers voted in November to recommend Jynneos for immunizing researchers and health care personnel who are at risk of exposure to smallpox or monkeypox.
The US emergency stockpile contains 100 million doses of an older smallpox vaccine called ACAM2000. But the vaccine contains live vaccinia virus and causes about six cases of myopericarditis (inflammation of the heart muscle) for every 1,000 people who receive it.
ACAM2000 cannot be used in pregnant women, infants, or immunocompromised people, exactly the people who most need protection against the monkeypox virus.
Jynneos, by contrast, has been shown to be safe in older adults, people with HIV or AIDS, and those who have received bone marrow transplants and are therefore immunocompromised.
The US stockpile once held 28 million doses of Jynneos, but all of those doses have expired, according to Paul Chaplin, chief executive of Bavarian Nordic. Federal health officials have said about 1,000 doses of Jynneos are available, but Bavarian Nordic has delivered thousands more in recent weeks, according to Dr. Chaplin.
In all, the United States has access to about a million doses, he said.
People infected with monkeypox can be vaccinated even a few days after exposure. They can also be treated with one of two approved smallpox drugs, tecovirimat and brincidofovir, which slow down the virus and give the immune system time to clear it.
What to know about the monkeypox virus
What is monkeypox? Monkeypox is an endemic virus in parts of central and western Africa. It is similar to smallpox, but less serious. It was discovered in 1958, after outbreaks occurred in monkeys kept for research, according to the Centers for Disease Control and Prevention.
The FDA has approved an oral form of tecovirimat, also called Tpoxx, to treat smallpox in adults and children weighing at least 13 kilograms, or 28.6 pounds, although the drug has never been tested in children.
The drug, made by the New York-based company Siga Technologies, is taken twice a day for 14 days and, in safety trials, appeared to have no serious side effects beyond gastric symptoms.
The US stockpile contains 1.7 million courses of tecovirimat. On May 12, before the monkeypox outbreak surfaced, the Defense Department purchased another $7.5 million worth of drug courses, about half of which would be delivered this year.
“A significant number of countries” have requested courses of the drug since the outbreak began, said Dennis Hruby, chief scientist at Siga. By the end of June, the company expects to have up to 190,000 treatments to distribute, he said.
The FDA worked with Siga to develop an intravenous formulation and approved it on May 19. This version can be used in patients who cannot take oral medicine due to blisters in the mouth.
Health Canada, the country’s national health department, approved tecovirimat in 2020, purchasing $13 million worth of doses, according to Dr. Hruby. The European Medicines Agency also endorsed the drug in January to treat all orthopox viruses, the viral family that includes both smallpox and monkeypox, but was still negotiating with the company when the outbreak emerged.
Both tecovirimat and brincidofovir were approved under the FDA’s Animal Rule, which allows the agency to rely on data from rodents or monkeys when it is unethical to test a drug in people.
The second drug, brincidofovir, is made by Chimerix and appears to have more side effects, including the risk of death, prompting the agency to issue a so-called black box warning, its strictest warning, on the drug’s use.
In the recent study of both drugs, brincidofovir “was not found to confer any convincing clinical benefit,” the researchers reported. But the study was too small and the treatment regimens offered to patients were too varied to draw any conclusions about the drugs’ effectiveness, said David Evans, a virologist at the University of Alberta who consults with Chimerix.
Those who can’t safely take either tecovirimat or brincidofovir (immunocompromised people, for example) can receive an immune therapy called vaccinia immune globulin, but only limited amounts are available.
The United States is helping to develop a cocktail of monoclonal antibodies that can block the monkeypox virus. Several vaccines are also in the early stages of development, including some based on smallpox.
In the long run, it may make sense for the United States to stockpile enough vaccines and drugs to protect the entire population, including those vaccinated against smallpox in childhood, said Dr. Seth Lederman, chief executive of Tonix, which is development of a horsepox-based vaccine.
Multiple studies suggest that people who have been vaccinated against smallpox may be protected from serious illness, if not infection. But developing even a few lesions would be enough to spread the virus to others, Dr. Lederman noted.
“In the case of something like monkeypox, I think the goal would be to keep people from getting injured,” he added.
The Tonix vaccine will not be available for use in the current outbreak. “Our approach will be to go slow and steady,” he said. “These problems are not going to go away.”