Mpox in Adults Over 50: Childhood Smallpox Shots and the JYNNEOS Vaccine

Americans over 50 were likely vaccinated against smallpox as children — routine childhood vaccination in the United States ended in 1971 — and that old vaccine gives some cross-protection against mpox. But older adults also tend to have more health problems that could make mpox worse. A CDC analysis of the 2022–2023 U.S. outbreak looked at how mpox played out in this age group, and whether the newer JYNNEOS vaccine still helped them.

Who got mpox

From May 10, 2022, to May 17, 2023, 30,401 mpox cases were reported in the United States, mostly among young adult men. Of 29,984 adults with probable or confirmed mpox:

• 2,909 (9.7 percent) were over 50, and 96.3 percent of them were cisgender men.
• Compared with adults aged 18 to 50, those over 50 more often had HIV and other immunocompromising conditions, such as an organ or stem cell transplant, active cancer or immunosuppressive treatment.
• Leaving out vaccinated people, adults over 50 were hospitalized and died about as often as younger adults, and had some symptoms less often.

Why is not clear. Childhood smallpox vaccination might offer some protection, perhaps making illness atypical or symptomless.

JYNNEOS still helped

Of adults over 50 with mpox, 27.6 percent had received at least one dose of JYNNEOS during the outbreak. Among the 1,020 over-50s whose vaccination status was known, HIV and immunocompromising conditions were about equally common in the vaccinated and unvaccinated — but the vaccinated had:

• less itching (pruritus);
• fewer constitutional symptoms such as fever, headache, malaise, muscle aches, chills or swollen lymph nodes;
• fewer hospitalizations.

So whatever protection childhood smallpox vaccine still gives, JYNNEOS likely added more — consistent with other studies of JYNNEOS. Studies show some long-lasting immune memory from childhood smallpox vaccination, but it may have faded.

The advice

Everyone at risk of mpox should get both doses of JYNNEOS, whether or not they were vaccinated against smallpox as children.

Limits

National case data often lacked HIV status, immune conditions, symptoms and vaccination status. Some information was self-reported. Childhood smallpox vaccination was assumed for everyone over 50, although practice varied in the United States and in the countries some patients came from. And only cases reported to health departments were counted.

Sources

Based on "Epidemiologic and Clinical Features of Mpox in Adults Aged >50 Years — United States, May 2022–May 2023," by Patrick C. Eustaquio and colleagues, Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; a work of the United States government in the public domain.