Re-exposure to wild-type virus stabilizes measles-specific antibody levels in late convalescent patients

Background: Infection with wild-type (wt) measles virus strains induces high antibody levels believed to provide life-long protection against disease. Objectives: Humoral immunity was followed up in convalescent measles patients to assess the persistence of specific antibodies after measles disease in individuals without and with documented re-exposure to wt virus. Study design: Paired sera were collected from 43 late convalescents (LC) before re-exposure and 3.7-4.8 years after re-exposure to at least one measles patient (LC+ group). Antibody persistence in this group was compared to paired sera from 43 age- and sex-matched controls without documented exposure to wt virus (LC- group). Paired sera were also obtained from 26 measles patients 1.3-1.7 and 3.8-4.1 years after they had recovered from measles to observe the waning of antibodies in early convalescents (EC group). Results: Antibody levels decreased by 12.1% (CI: 3.2-20.3%, p = 0.01) within 6.3 years in the LC- group of late convalescent measles patients. In contrast, in the LC+ group GMT of first and second sera were virtually identical, indicating that exposure to wt virus stabilizes antibody levels even in absence of a detectable secondary immune response. In a subset of late convalescents of group LC+ with a secondary immune response, antibody waning after re-exposure was as high as 15.6%/year (CI: 13.0-17.7%/year), corresponding to a half-life of 4.1 years (CI: 3.5-5.0 years), but antibodies were still higher than before re-exposure. In the EC group GMT decreased by 6.5% (95% CI: -13.3% to +0.1%) during 2.5 years but significance was low (p = 0.08). Conclusion: The maintenance of antibody levels in convalescent measles patients is at least partially dependant on recurrent exposure to circulating wt virus.