Eradication of smallpox could be a prelude to smallpox epidemicExBulletin

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Big successes can also have unexpected consequences. So too was the eradication of smallpox, one of the world's greatest victories. That outcome may have set the stage for a different kind of epidemic that we're dealing with today. And now there's new evidence to support that theory. NPR's Gabriel Emanuel reports.

GABRIEL EMANUEL, BYLINE: Eugene Vanwen spends his days thinking about mpox, formerly known as monkeypox.

Eugene Vanwen: The number of mpox cases is increasing rapidly.

Emmanuel: He studies infectious diseases at the Institute of Tropical Medicine in Belgium. More than 100,000 mpox cases have been confirmed worldwide in the past few years. This is several times more than the previous year. I have a question for Mr. Van Wen.

Van Wen: I mean, where did that come from?

Emanuel: Why are the numbers rising so quickly? Why are mpox appearing in new locations?

Van Wen: These are all questions that we don't understand.

Emmanuel: Researchers think there are many factors at play. Vanwen decided to look back at all the mpox cases confirmed in the Democratic Republic of the Congo in recent decades and see what he could find.

Vanwen: We graphed everyone's age.

Emanuel: And this data shows that almost all mpox patients were born after a certain point. Vanwen says to understand why this is the case, you need to go back to the remote depths of Congo's rainforest in 1970. That's where the mother took her nine-month-old boy on an ill-fated trip to visit his grandmother.

William Moss: So the child got sick soon after arriving in his grandmother's village.

EMANUEL: William Moss is an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

Moss: He developed a fever and two days later developed a rash.

EMANUEL: Moss says he sounded the alarm because the rash looked so much like smallpox. The world was so close to eradicating smallpox that every patient with a suspicious rash or lesion needed to be investigated to prove that smallpox had truly been eradicated. Doctors at a local hospital took a scab from the boy and sent it to a research institute in Moscow. The answer came back: it wasn't smallpox. This was monkeypox.

Moss: That was a surprise to everyone, obviously.

Emanuel: It was the first known human case. That little boy, he was patient zero. A scientific investigator soon appeared.

MOSS: They interviewed the family. They interviewed neighbors. They tried to identify contacts and routes of infection.

Emanuel: One of the things they discovered was that this boy was the only one in his family who couldn't get the smallpox vaccination. This was the first clue that smallpox and mpox were very closely related and that the smallpox vaccine gave people some degree of immunity to mpox.

Moss: As more and more monkeypox cases were identified, it became clear that these cases were occurring in people who had not been vaccinated against smallpox.

Emanuel: But back in the 1970s, almost everyone was vaccinated. Therefore, the total number of mpox cases was very small. But then 1980 came. Smallpox was declared eradicated, and vaccinations soon ended. Eugene Vanwen looked at all the data from the study and found the impact of stopping vaccination. It was like an invisible line in the sand. People born before then developed immunity to mpox. People born after that time had no immunity. The end of smallpox vaccination marked the beginning of mpox and set the stage for the surge in mpox cases seen today. Vanwen points to another lesson from this history: the power of vaccination.

Van Wen: Therefore, vaccination is highly needed as a means of controlling mpox. yes.

Emmanuel: Vaccines were the key to defeating smallpox. The same likely applies to mpox, he says. Gabriel Emanuel, NPR News.

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