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Who is protected against monkeypox?

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

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

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

Older people who have been vaccinated can be infected but are likely to recover with only mild symptoms.

“The bottom line is that even those who were vaccinated several decades ago retain a very, very high level of antibodies and the ability to neutralize the virus,” said Dr. Luigi Ferrucci, scientific director of the National Institute of 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 ceased in 1972. The military continued its vaccination program until 1991 as a precaution against a bioterrorist attack.

Questions about the durability of the smallpox vaccine rose after a 2001 anthrax attack, said Dr. Anthony S. Fauci, the Biden administration’s top infectious disease adviser. It was reasonable to assume that most vaccinated people were still protected, he said, “but the durability of protection varies from person to person.”

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

The monkeypox outbreak has grown to include around 260 confirmed cases with dozens more under investigation in 21 countries. The infection begins with respiratory symptoms, but develops into a distinct rash, first in the mouth, then on the palms of the hands and soles of the feet, and gradually over the rest of the body. The rash eventually lifts, turning into pus-filled blisters.

Each pustule contains live virus, and a ruptured blister can contaminate bed linens and other items, putting close contacts at risk. Infected people should also be very careful not to rub their eyes as the virus can destroy sight.

“Before Jenner developed the smallpox vaccine, the number one cause of blindness in the world was smallpox,” said Mark Slifka, an immunologist at Oregon Health and Science University. Infected people are contagious until the pustules form and break off, he said.

Dr. Slifka and other experts have pointed out that while monkeypox can be serious and even fatal, the current outbreak is unlikely to turn into a major outbreak.

“We’re lucky to have vaccines and treatments — things that can mitigate all of this,” 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.”

Monkeypox takes up to 12 days to cause symptoms, giving doctors a window of at least five days after exposure to vaccinate and prevent disease. (The approach, called post-exposure prophylaxis, is not an option for Covid patients because the coronavirus can start ravaging the body just days after exposure.)

The monkeypox virus does not spread in the absence of symptoms. Careful surveillance, isolation of infected people, contact tracing and quarantine of contacts should contain the outbreak, Dr. Rimoin said.

The majority of those infected are currently men under the age of 50, and many identify as gay or bisexual, which may reflect possible origins of the outbreak at a Gay Pride event in the Canary Islands. (The outbreak could just as well have started among heterosexuals at a big event, experts said.)

No deaths have been reported. But experts are particularly concerned about close contacts who are children, elderly or have weakened immune systems for other reasons.

There are conflicting opinions about the duration of immunity to smallpox vaccination.

The Centers for Disease Control and Prevention recommends smallpox vaccine boosters every three years, but only “for those at risk of occupational exposure,” agency spokesman David Daigle said in a statement. .

“Until we know more, we will use available vaccine stocks for people who have been in close contact with known cases and people most at risk of exposure through their work, such as health workers. healthcare treating patients with monkeypox,” he said.

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

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

In another study, Dr. Slifka and his colleagues showed that the antibodies produced by even a single dose of the smallpox vaccine decline very slowly in the body, halving after about 92 years.

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

If smallpox started to spread, it would make sense to vaccinate anyone exposed because of its high death rate, regardless of previous vaccination, said Gigi Gronvall, biosecurity expert at the Johns Hopkins Center for Health Security.

“We wouldn’t want to risk anyone being left unprotected,” she said.

But that’s no longer necessary now, she added: “It’s monkey pox.”

Antibody laboratory evidence does not prove that smallpox vaccination can protect against monkeypox. But to answer that question would require study participants to be deliberately infected with smallpox or a related virus, a clearly unethical experiment.

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

Yet one way to study vaccine effectiveness in humans is to collect evidence during an outbreak. That’s exactly what Dr. Slifka’s team did in 2003, when dozens of Americans were infected with monkeypox after being exposed to infected prairie dogs.

The researchers traveled to Milwaukee and took 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 to an average of 33 in those who were not vaccinated.

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

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. Their 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 taken on particular importance as the number of cases worldwide has increased. Monkeypox re-emerged among Nigerians in 2017 and there have since been around 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.

People in African villages used to contract monkeypox from animals while hunting, but they rarely infected others. “It’s only very recently, like the last few years, that we’ve started to see this,” Dr Rimoin said of larger outbreaks.

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

Diminishing immunity, coupled with a growing population and increased proximity to wild animals, could lead to more frequent outbreaks of monkeypox, Dr. Rimoin and colleagues warned in 2010.

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

“If monkeypox were to become established in a wildlife reservoir outside of Africa, the public health setback would be enormous,” Dr Rimoin said. “It is, I think, a legitimate concern.”


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