When someone seroconverts, their blood changes from being negative for a virus to being positive for that virus.
Seroconverting is usually a big deal because it means someone may have gotten sick with a virus.
Examples:
After a few weeks, the person seroconverts and now has the virus in their blood.
The test shows that she seroconverts for the virus.
He seroconverts after being exposed to the virus.
The cat seroconverts after being bitten by a sick mouse.
The superhero seroconverts after being exposed to the alien virus.
The plant seroconverts after being infected with the new virus.