RESUMO
Objective: To determine the concentration and rate of decay of maternal IgG antibodies against measles prevalence in infants of vaccinated or naturally infected mothers and study initial measles immunization occurs in nine-month-old children. Methods: In total, 401 pregnant women and the same number of their subsequent newborns were recruited in the Bavi district of Hanoi in 2016-2017; they were divided into two groups: Older women (born before 1985, n=201) and younger women (born after 1990, n=200). Samples were collected at five time-points; week 36 of pregnancy, birth (cord), and 3, 6, and 9 months after birth. Measles-specific IgG antibody levels were recorded. Results: In total, 77.06% of the 401 pregnant women were seropositive for measles-specific IgG antibodies. A significantly greater proportion of mothers aged 30 and older (88.06%) and their newborn (93.53%) were seropositive compared to the mothers aged 25 and younger (66.00%), and their newborn (72.00%) (P<0.001). The infants of older mothers had significantly higher geometric mean titres (GMT) of measles IgG antibodies than the infants of younger mothers (P<0.001) at all time-points of the study period. The proportion of measles IgG antibodies together with GMT decreased from 82.97% (506.96) at the age of three months to 23.19% (45.22) at the age of nine months. Conclusions: This study provides a profile of maternal antibodies against measles in Vietnamese infants and investigates the early susceptibility to measles in both the infants of vaccinated mothers and mothers with naturally acquired immunity. These data suggest that determining the appropriate age for measles vaccination is paramount for the elimination of measles in Vietnam.