measles抗體消失很快，不要delay打針

How Long Does Passive Immunity to Measles Last in Infants?

Maternal antibodies to measles in infants might completely disappear before the first measles vaccination.

During the first year of life, maternal antibodies provide protection to infants against infectious diseases such as measles. The gestational age of the infant, maternal age, and whether the mother's immunity comes from vaccination or natural disease can affect the amount of maternal antibodies present. Investigators in Belgium prospectively examined maternal antibodies against measles in 207 women (age range, 18–40) and their 210 children between April 2006 and November 2008. Infants born before 36 weeks' gestation or weighing <2400>

Blood samples were obtained from mothers to measure measles IgG antibodies at 36 weeks' gestation, at birth (via cord blood), and in infants at ages 1, 3, 6 or 9 months, and at 12 months. Eighty-seven women were vaccinated against measles, and 120 were naturally immune. At 36 weeks' gestation, 26% of vaccinated mothers and 8% of naturally immune mothers had IgG levels below the protective threshold, and vaccinated women had significantly lower mean titers (779 vs. 2687 mIU/mL). Infants of vaccinated mothers continued to have significantly lower mean titers at each time point. At 6 months, only one infant of a vaccinated mother had an IgG level above the threshold (vs. 11 in the naturally immune group). By 9 months, no infant in either group had levels above the threshold. The rate of decay of passive immunity was steeper in infants of naturally immune women, but the median time to loss of immunity was longer than that in infants of vaccinated mothers (3.78 vs. 0.97 months). Breast-feeding, parity, birth weight, educational level, day-care attendance, and cesarean delivery did not significantly alter the results.

Comment: One major flaw of this study is that the authors set the measles antibody threshold level based on results from optical density studies, but whether this level is an actual clinical threshold for measles protection in infants is unclear. Nevertheless, this study demonstrates that an infant's passive immunity to measles wears off before the infant receives the first measles vaccination, especially if parents choose to delay the first vaccine. These data provide one more reason for parents to vaccinate their children according to the recommended schedule.

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