Persistence of measles antibodies after 2 doses of measles vaccine in a postelimination environment.
OBJECTIVE
To evaluate the persistence of measles antibodies after 2 doses of measles vaccine in a setting where exposure to wild-type measles was unlikely. Measles was declared eliminated from the United States in 2000, an achievement attributed to effective implementation of a routine 2-dose vaccination policy. Some have questioned whether measles transmission could resume if immunity wanes in the absence of boosting from wild-type measles.


METHODS
Prospective, observational, volunteer cohort study.


METHODS
Rural Wisconsin health maintenance organization.


METHODS
Children who received the second measles vaccine dose at kindergarten (aged 4-6 years) or middle school (aged 10-12 years) in 1994 or 1995. Serum samples were collected periodically during a 10-year period for the kindergarten group and a 5-year period for the middle school group.


METHODS
Second dose of measles vaccine.


METHODS
Measles antibody levels were assessed by plaque-reduction neutralization: titers less than 8 mIU/mL were considered seronegative and suggestive of susceptibility to measles, and titers of 120 mIU/mL or less were considered low and suggestive of potential susceptibility.


RESULTS
During the study period, no measles was reported in the study area. Voluntary attrition reduced the study population from 621 at enrollment to 364 (58.6%) by study end. Before the second dose, 3.1% (19/621) had low titers, of whom 74% (14/19) were antibody-negative, with geometric mean titers being significantly higher in kindergarteners (1559 mIU/mL) than in middle schoolers (757 mIU/mL) and rates of negativity significantly lower (1.0% [3/312] vs 3.6% [11/309]). One month after the second dose, 0.2% (1/612) had low titers and none was seronegative, with geometric mean titers being significantly higher in kindergarteners (2814 mIU/mL) than in middle schoolers (1672 mIU/mL). By study end, 4.9% (18/364) had low titers and none was seronegative, with no significant difference in geometric mean titers between kindergarteners (641 mIU/mL) and middle schoolers (737 mIU/mL) when both groups were aged 15 years. Projections suggest that the proportion of persons with low antibody levels may increase over time.


CONCLUSIONS
Measles antibody persisted in all vaccinees available for follow-up 10 years after a second dose of vaccine, with no seronegative results detected. Declining titers suggest the need for vigilance in ensuring disease protection for the vaccinated population.
LeBaron
Charles W
CW
Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. clebaron@cdc.gov
Beeler
Judith
J
Sullivan
Bradley J
BJ
Forghani
Bagher
B
Bi
Daoling
D
Beck
Carol
C
Audet
Susette
S
Gargiullo
Paul
P
D000293:Adolescent; D000914:Antibodies, Viral / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D008457:Measles / Q000517:prevention & control*; D008458:Measles Vaccine / Q000008:administration & dosage*; D008459:Measles virus / Q000276:immunology*; D011446:Prospective Studies
D000914:Antibodies, Viral; D008458:Measles Vaccine