Who is protected from monkeypox?

For a world tired of battling the coronavirus, the monkeypox outbreak poses a key question: Am I at risk?

The answer is reassuring. Most children and adults with a healthy immune system are likely to avoid serious illness, experts said in interviews. But there are two risk groups.

One includes infants under six months. However, they are not yet affected by the current outbreak. And many older adults, the group most likely to succumb to the monkeypox virus, are at least somewhat protected by decades-old smallpox vaccines, studies suggest.

Vaccinated older adults can become infected, but are likely to have only mild symptoms.

“The bottom line is that even those who were vaccinated many decades earlier retain very, very high levels of antibodies and the ability to neutralize the virus,” said Dr. Luigi Ferrucci, Scientific Director of the National Institute on Aging.

“Even if they were vaccinated 50 years ago, that protection should still be there,” he said.

In the United States, routine vaccination against smallpox was discontinued in 1972. The military continued its vaccination program until 1991 as a precaution against a bioterrorist attack.

A 2001 anthrax attack raised questions about the durability of the smallpox vaccine, Dr. Anthony S. Fauci, the Biden administration’s chief adviser on infectious diseases. It’s reasonable to assume that most vaccinated people would still be protected, he said, “but the duration of protection varies from person to person.”

“We cannot guarantee that a person who has been vaccinated against smallpox will still be protected against monkeypox,” said Dr. fauci

The monkeypox outbreak has grown to about 260 confirmed cases, with more being investigated in 21 countries.

In the United States, the Centers for Disease Control and Prevention is tracking nine cases in seven states, not all of which have traveled to countries where monkeypox is endemic in the past. That suggests there may already be some level of community transmission, said Dr. Rochelle Walensky, the agency’s director, told reporters on Thursday.

dr Walensky said 74 labs in 46 states have access to a test that can detect monkeypox, and together they can test up to 7,000 samples a week. The agency is working to expand that capacity, she said, adding, “We’ve been preparing for this type of outbreak for decades.”

Monkeypox infection begins with respiratory symptoms but progresses to a distinct skin rash, first in the mouth, then on the palms and soles of the feet, and gradually the rest of the body. The rash eventually becomes raised and grows into pus-filled blisters.

Each pustule contains live viruses, and a ruptured blister can contaminate linens and other items and endanger close contacts. Infected people should also be very careful when rubbing their eyes, as the virus can destroy eyesight.

“Before Jenner developed the smallpox vaccine, smallpox was the leading cause of blindness worldwide,” said Mark Slifka, an immunologist at Oregon Health and Science University. Infected people are contagious until the pustules crust over and shed, he said.

dr Slifka and other experts stressed that while monkeypox can be serious and even deadly, the current outbreak is unlikely to swell into a major epidemic.

“We’re fortunate to have vaccines and therapeutics — things that can alleviate all of that,” said Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who has studied monkeypox in Africa. “We have the ability to stop this virus.”

It takes up to 12 days for monkeypox to produce symptoms, giving doctors a window of at least five days after exposure to the vaccine and preventing the disease. (The approach, dubbed post-exposure prophylaxis, is not an option for Covid patients because the coronavirus can begin to ravage the body just days after exposure.)

The monkeypox virus does not spread without symptoms. Careful surveillance, isolation of infected people, contact tracing and quarantine of contacts should contain the outbreak, said Dr. rimoin

The majority of those infected are currently men under 50 and many identify as gay or bisexual, possibly linked to a gay pride event in the Canary Islands. (The outbreak might as well have started at a large event among straight people, experts said.)

“The risk of exposure is not limited to any particular group,” said Dr. Walensky on Thursday. “Our priority is to help everyone make informed decisions to protect their health and the health of their community, and that starts with awareness guided by science, not stigma.”

No deaths were reported. But experts are particularly concerned about close contacts who are children, older adults, or who otherwise have weak immune systems.

There are conflicting opinions as to how long immunity to smallpox vaccination lasts.

The CDC recommends booster shots against smallpox every three years, but only “for people at risk of occupational exposure,” David Daigle, a spokesman for the agency, said in a statement.

“Until we know more, we will use available stocks of vaccine for people who have been in close contact with known cases and for people who are at the highest risk of exposure through their work, such as E.g. medical staff treating monkeypox patients,” he said.

The United States and several European countries have begun immunizing close contacts of infected patients, an approach known as ring vaccination.

Many of the most vulnerable groups may already be protected. In one study, Dr. Slifka and his colleagues collected blood from 306 vaccinated volunteers, some of whom had been vaccinated decades earlier, including one who had been vaccinated 75 years earlier. Most of them retained high antibodies to smallpox.

In another study, Dr. Slifka and his colleagues found that antibodies produced by even a single dose of the smallpox vaccine break down very slowly in the body, falling by half after about 92 years.

dr Ferrucci and his colleagues at the NIH, as well as other teams, have also found that antibody levels persist decades after vaccination. Some studies have found that other branches of the immune system also begin to decline, but antibodies produced by the smallpox vaccine alone may be enough to protect against monkeypox.

If smallpox were to spread, it would make sense to immunize everyone exposed because of its high mortality rate, regardless of previous vaccination, said Gigi Gronvall, a biosecurity expert at the Johns Hopkins Center for Health Security.

“We wouldn’t want to take the risk of leaving anyone unprotected,” she said.

But that’s not necessary now, she added: “It’s monkeypox.”

Laboratory detection of antibodies does not prove that smallpox vaccination can protect against monkeypox. However, answering that question would require the study participants to be intentionally infected with smallpox or a related virus, an obviously unethical experiment.

For the same reason, newer smallpox vaccines and drugs have only been tested on animals.

However, one way to study the vaccine’s effectiveness in humans is to gather evidence during an outbreak. That’s exactly what Dr. Slifka’s team in 2003 when dozens of Americans contracted monkeypox after exposure to infected prairie dogs.

The researchers flew to Milwaukee and drew blood from 28 people who had been exposed to the infected prairie dogs. Of the eight people who had previously been vaccinated, five developed an average of three pus-filled blisters, compared with an average of 33 in the unvaccinated.

The other three vaccinated people had no symptoms at all. “They didn’t even know they were infected,” said Dr. Slifka.

Another study of this outbreak found that in a family of three, the previously vaccinated father developed only two monkeypox lesions, compared to 200 in the unvaccinated mother. Her unvaccinated 6-year-old daughter had about 90 lesions and was in a coma for 12 days.

Questions about the durability of vaccine protection against monkeypox have become particularly important in view of the increasing number of cases worldwide. Monkeypox reappeared among people in Nigeria in 2017, and since then there have been about 200 confirmed cases and 500 suspected cases.

The Democratic Republic of the Congo has recorded 58 deaths and nearly 1,300 suspected cases since the beginning of this year.

In the past, people in African villages contracted monkeypox from animals while hunting, but rarely infected others. “It’s only recently, around the last few years, that we’ve started to see this,” said Dr. Rimoin on major eruptions.

The eradication of smallpox, while one of the greatest public health achievements, has left populations vulnerable to the virus and its cousins.

Declining immunity, coupled with population growth and closer proximity to wildlife, could lead to more frequent monkeypox outbreaks, warned Dr. Rimoin and her colleagues 2010.

Unchecked outbreaks, especially in immunocompromised people, would give the virus more opportunity to acquire mutations that make it more resilient – in humans and animals.

“If monkeypox became established in a wildlife reservoir outside of Africa, the public health blow would be enormous,” said Dr. rimoin “I think that’s a legitimate concern.”