Antibody levels against the novel coronavirus rose and then held steady for up to four months in more than 90% of recovered COVID-19 patients in Iceland, according to a study published on Tuesday. In previous studies, antibody levels dropped sharply within a few months after COVID-19, raising questions about the duration of immunity that infection may provide. The new finding may have implications for reinfection risks and vaccine durability, said Kari Stefansson, chief executive of deCode Genetics, which conducted the study.