Deficiency of the humoral immune response to measles vaccine in infants immunized at age 6 months.
BACKGROUND
Measles causes serious morbidity in infants, with the highest risk among those who are 6 to 12 months of age. In the United States, measles vaccine has been given at age 12 to 15 months to minimize interference by passive antibodies and to achieve the high seroprevalence required for herd immunity. Infants of mothers with vaccine-induced immunity may lose passively acquired antibodies before 12 months, leaving them susceptible to measles infection.


OBJECTIVE
To assess the immunogenicity of measles vaccine in infants younger than 12 months.


METHODS
Cohort study conducted before and after measles immunization.


METHODS
Pediatric clinic in Palo Alto, Calif.


METHODS
Infants 6 (n = 27), 9 (n = 26), and 12 (n = 34) months of age were enrolled; 72 provided both initial and follow-up samples.


METHODS
Evaluation of immunogenicity before and 12 weeks after measles vaccination, including measles neutralizing antibody titers, measles-specific T-cell proliferation, and cytokine profiles.


RESULTS
Measles neutralizing antibodies were present before vaccination in 52% (12/23), 35% (7/20), and 0% (0/22) of 6-, 9-, and 12-month-old infants, respectively. In the absence of detectable passive antibodies, geometric mean titers after vaccination were significantly lower in 6-month-old infants compared with 9-month-old infants (27 vs 578, P = .01) and 12-month-old infants (27 vs 972, P=.001). The seroconversion rate, defined as a 4-fold rise in antibody titer, in these 6-month-old infants was only 67%, and only 36% of these infants achieved seroprotective neutralizing antibody titers of 120 or higher after vaccination compared with 100% of 9- and 12-month-old infants lacking detectable passive antibody prior to vaccination. T-cell proliferation and cytokine responses to measles did not differ with age.


CONCLUSIONS
Humoral immunity was deficient in 6-month-old infants given measles vaccine, even in the absence of detectable passively acquired neutralizing antibodies. Comparison of their responses with those of 9- and 12-month-old infants indicates that a developmental maturation of the immune response to measles may occur during the first year of life, which affects the immunogenicity of measles vaccine.
Department of Pediatrics, Stanford University School of Medicine, Calif 94305-5208, USA. drhayley@leland.stanford.edu
H A
HA
Gans
A M
AM
Arvin
J
J
Galinus
L
L
Logan
R
R
DeHovitz
Y
Y
Maldonado
D000367:Age Factors; D000914:Antibodies, Viral / Q000097:blood*; D000917:Antibody Formation; D015331:Cohort Studies; D016207:Cytokines / Q000096:biosynthesis; D006801:Humans; D007112:Immunity, Maternally-Acquired; D007223:Infant; D008457:Measles / Q000276:immunology*; D008458:Measles Vaccine / Q000276:immunology*; D008459:Measles virus / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology
D000914:Antibodies, Viral; D016207:Cytokines; D008458:Measles Vaccine