Which virus was the first to be eradicated globally?

The first virus eradicated globally was variola virus, the causative virus of smallpox.

Smallpox was a human disease caused by variola virus, an orthopoxvirus with no known animal reservoir. That human-only cycle was crucial to eradication: once every chain of person-to-person transmission was interrupted, the virus had nowhere else to persist. A highly effective vaccine and international surveillance campaign made that possible.

The last naturally occurring case was diagnosed in Somalia on 26 October 1977, in Ali Maow Maalin. The World Health Organization formally certified smallpox eradicated in 1980. The campaign relied heavily on surveillance and containment, including ring vaccination, in which close contacts and people near a case were vaccinated.

Variola virus is often confused with vaccinia virus, the related virus used in the smallpox vaccine. Rubella, measles, and polioviruses have all been targeted by major elimination campaigns, but none has been eradicated globally. Smallpox therefore remains the landmark example of successful human viral eradication, although authorized laboratories still retain variola virus stocks for research.