Measles vaccine immunogenicity in 6- versus 15-month-old infants born to mothers in the measles vaccine era.
OBJECTIVE
The low titer of measles antibody in infants of mothers with vaccine-induced immunity may allow immunization against measles before 15 months of age.


METHODS
Six- and 15-month-old infants born to mothers < or = 30 years of age with no history of measles were recruited. Infants enrolled at 6 months of age were immunized with monovalent measles vaccine (Attenuvax), and maternal serum and infant pre- and postvaccination sera were obtained. Those enrolled for primary vaccination at 15 months of age received either Attenuvax (N = 12) or M-M-RII (N = 3). Six-month-old infants were revaccinated with M-M-RII at 15 months of age; pre- and postrevaccination sera were again obtained. Three antibody assays were used: a measles neutralizing assay (NT) and two enzyme immunoassays (EIA) for measles IgG and measles IgM.


RESULTS
Among primary vaccinees, 14 of 19 infants aged 6 months (74%) developed NT antibody, as did 15 of 15 infants aged 15 months (100%). The reciprocal geometric mean titer of 6-month-old seroresponders was 23.3, significantly lower than that of the 15-month-old primary vaccinees (87.7, P < .001). Primary seroconversion rates by EIA were 53% for 6-month-old infants and 100% for those aged 15 months. Revaccination of infants who had received Attenuvax at 6 months of age resulted in 100% NT positivity; the geometric mean titer rose to equal that of the group given primary immunization at 15 months of age. Measles IgM antibody was detected in 10 of 14 infants tested 1 month after primary vaccination at 15 months, but was not detected in any of the revaccinated infants after the second dose at 15 months of age (P < .001).


CONCLUSIONS
1) Immunization with measles vaccine in infants born to vaccine-immune mothers at 6 months of age induced NT antibody in 74% of infants. 2) Revaccination of prior 6-month-old vaccinees at 15 months resulted in antibody titers equivalent to 15-month-old vaccinees. 3) Lack of an IgM response following revaccination suggests that even seronegative infants may be primed to respond on re-exposure to measles.
Johnson
C E
CE
Department of Pediatrics, Case Western Reserve School of Medicine, West Point, PA.
Nalin
D R
DR
Chui
L W
LW
Whitwell
J
J
Marusyk
R G
RG
Kumar
M L
ML
D000328:Adult; D000914:Antibodies, Viral / Q000032:analysis*; D005260:Female; D006801:Humans; D007112:Immunity, Maternally-Acquired / Q000276:immunology*; D007115:Immunization Schedule; D007117:Immunization, Secondary; D007124:Immunoenzyme Techniques; D007223:Infant; D008297:Male; D008457:Measles / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D008458:Measles Vaccine / Q000008:administration & dosage / Q000276:immunology; D008459:Measles virus / Q000276:immunology*
D000914:Antibodies, Viral; D008458:Measles Vaccine