Their antibodies were not permanent, they lasted 11 months. However, the virus is no longer "novel" for their bodies. Their bodies know what to do the next time they get covid or a similar variant. They will likely still be able to get infected, but it won't be a severe illness, more likely a common cold. The vaccine is not permanent either, and will likely need booster shots in the future to keep the antibodies alive and well. It will likely be a yearly thing similar to the flu for the next few years.