Scientists are sounding the alarm that waning immunity from smallpox since its eradication might have left the world vulnerable to monkeypox, the Daily Mail reported on Wednesday.
The World Health Organization declared smallpox eradicated in 1980 after a nearly 20-year campaign to distribute vaccines against it. However, since the last confirmed natural case in 1977, countries worldwide have ditched requirements for the vaccine.
Dr. Romulus Breban, a researcher at the Pasteur Institute in Paris, told The Guardian that the outbreak was "waiting to happen" because of almost no immunity to smallpox by generations after vaccine distribution was halted.
A University of Edinburgh professor, Neil Mabbott, parroted Breban's statement to the Mail, warning that people over 50 could be the only group protected against monkeypox.
"Although the level of immunity will wane in time, smallpox vaccination provides long-lasting protection," Mabbott said. "Some estimates suggest this may last for decades."
Some experts disagree with Breban and Mabbott. Professor Paul Hunter, an infectious disease expert at the University of East Anglia, said it was "difficult to say" if waning smallpox immunity led to the monkeypox outbreak.
"I think it would be a push to assume [the smallpox vaccine] significant protection 50 years later," Hunter told the Mail, noting that the smallpox vaccine was only fully effective for "about five years."
"There may still be some modifying effect, but I don't know," he added.
The Imvanex vaccine by Danish biotechnology company Bavarian Nordic A/S is up to 85% effective against monkeypox, despite initially being produced to fight smallpox. Antivirals and therapies are also reportedly effective.
Nearly 20 countries where monkeypox is not endemic have reported outbreaks of the virus, with more than 100 confirmed or suspected infections, according to Reuters.
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