Decades-Old Smallpox Vaccination May Still Protect You Against Monkeypox

If you are older than 50, you were almost certainly vaccinated against smallpox during childhood. Many people still carry a small, pea-sized scar on their upper arm — a reminder of a global vaccination effort that successfully eradicated smallpox in 1980.

The encouraging news is that this vaccination may still offer meaningful protection against monkeypox, according to Dr. Michael Mosley, a British medical broadcaster and physician. Although smallpox vaccination programs ended decades ago, their long-term effects appear to be surprisingly durable.

Smallpox vaccination campaigns continued in both the United Kingdom and the United States until about 1971–1972. That means most people born before this time — essentially those aged 50 and older — received the shot and still retain some level of immunity, according to reporting from The Daily Mail and The New York Times.

Because smallpox and monkeypox belong to the same family of viruses, the smallpox vaccine has been shown to provide roughly 85% protection against monkeypox infection. This makes it one of the most cross-protective vaccines in medical history.

What experts find especially remarkable is that immunity can persist for a lifetime. Studies have found that individuals vaccinated as children continue to show strong antibody responses decades later. One of the longest-documented cases involved a person still exhibiting immunity more than 90 years after vaccination — a striking example of long-lasting immune memory.

Older adults who were vaccinated long ago may still become infected with monkeypox, but research suggests they tend to experience milder symptoms and recover more quickly than those without prior immunity.

Dr. Luigi Ferrucci, scientific director at the U.S. National Institute on Aging, emphasized that people vaccinated decades earlier maintain “high levels of antibodies and strong virus-neutralizing capability.” A visible smallpox vaccination scar remains a good indicator that some protection is likely still present.

Even so, experts caution that immunity varies from person to person. Dr. Anthony S. Fauci, the White House’s chief infectious disease adviser, noted that while most vaccinated individuals retain protection, it is not absolute.
“We cannot guarantee that someone vaccinated against smallpox will still be protected from monkeypox,” he told The New York Times. Factors such as age, health conditions, and overall immune function can influence protection levels.

Should Unvaccinated People Be Worried?

The short answer is no. Experts stress that most healthy children and adults have a very low risk of developing severe illness from monkeypox. The virus typically causes fever, rash, and fatigue, but the vast majority of cases resolve without complications, especially with proper medical care and monitoring.

Who Is at Higher Risk?

Two groups face a higher risk of severe outcomes:

1. Infants under 6 months, whose immune systems are not fully developed. Fortunately, this group has not been significantly affected in the current outbreak.

2. Older adults, who may have age-related immune decline. Even so, studies show they still benefit from residual protection from their childhood smallpox vaccination, helping lessen symptom severity.

Anne Rimoin, an epidemiologist at the University of California, Los Angeles, who has studied monkeypox in Central Africa for years, highlighted the advantage modern health systems have today.
“We are fortunate to have vaccines and treatments,” she said. “We have the ability to contain this virus.”

The Bottom Line: Monkeypox Can Be Contained

Monkeypox does not spread before symptoms appear — an important distinction from viruses like COVID-19. According to Dr. Rimoin, rapid identification of cases, isolating infected individuals, tracing contacts, and quarantining exposed people are the key steps needed to stop an outbreak.

Coupled with the lingering protection in older adults and the availability of newer smallpox-based vaccines, experts say we are well-equipped to keep monkeypox under control.