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• Posted May 25, 2023

Got Smallpox Vaccine as a Child? You're Probably Immune to Mpox

Smallpox vaccines, which were routinely given into the 1970s, seem to provide protection from mpox, a new study says.

The mpox virus, responsible for a worldwide outbreak last year, could surge again this summer, public health experts have warned. It was previously called monkeypox.

Researchers at the Karolinska Institute in Sweden wondered whether the smallpox vaccine would offer some level of immunity against mpox due to a residual memory response. Mpox is among orthopoxviruses that have similarities to smallpox, which was eradicated in the mid-1970s.

"The findings from our study demonstrate that this holds true, indicating that the memory cells exhibit remarkable longevity and possess the ability to identify closely related viruses like the mpox virus," said co-author Marcus Buggert, a researcher at Karolinska's Center for Infectious Medicine.

"They can offer overlapping immunity or cross-reactive protection," Buggert added in an institute news release.

The team examined T-cell immune response in 105 healthy blood donors, finding that people born before 1976 had a notably robust immune response against both viral types.

They then evaluated the immune response in 22 men who recently contracted mpox, finding that they also had a vigorous immune response to the virus.

The authors said this suggests the potential for future immunity among those individuals.

The sample size was insufficient for researchers to determine how much protection prior vaccination offered, but a recently published British study sheds light on that, Buggert said.

"According to this study, the smallpox vaccine has demonstrated the potential to offer approximately 80% protection against mpox,"Buggert said.

Mpox is primarily transmitted through close physical contact with an infected individual, such as during sexual activity. In the 2022 outbreak, it was commonly spread among gay and bisexual men.

Symptoms include blistering, sores, rashes, fever and swollen glands.

The study findings were published recently in the journal Cell Host & Microbe.

More information

The World Health Organization has more on mpox.

SOURCE: Karolinska Institute, news release, May 23, 2023