Babies Lose Maternal Measles Antibodies After a Few Months

Reuters Health Information

By Frederik Joelving

NEW YORK (Reuters Health) May 18 - Maternal measles antibodies wane earlier than previously thought, leaving infants susceptible to the virus for several months under current immunization guidelines, Belgian researchers report in a May 18th online paper in BMJ.

While not recommending an overhaul of general vaccination age -- currently 12 months in both Belgium and the US -- they said infants with special exposure to measles may need to be immunized at six months.

"We could recommend to vaccinate earlier, but because of good coverage here in Belgium we do not want to lose people" by adding an extra trip to the doctor, said lead author Dr. Elke Leuridan of the University of Antwerp in Wilrijk, Belgium.

Dr. Leuridan and colleagues studied 207 healthy mother-child infant pairs. Eighty-seven of the mothers had been vaccinated against measles and 120 had natural immunity.

The researchers collected venous blood during pregnancy (week 36, 10 ml), at birth (cord blood, 10 ml) and in infants at 1, 3 and 12 months (2 ml). In addition, they took samples randomly at either 6 or 9 months.

They used an enzyme-linked immunosorbent assay to measure the amount of measles immunoglobulin G (IgG) in the blood, calibrating the assay against the international reference preparation of measles antigen. The samples were considered positive if the corrected optical density was greater than 0.2, and negative if it was less than 0.1.

Overall, vaccinated women had lower IgG titers than naturally immune women (779 vs. 2687 milli-International Units per milliliter, or mIU/mL; p<0.001). The same pattern was seen for the infants at all ages (p<0.001).

Maternal antibodies persisted for a median of 3.8 months in infants of naturally immune mothers and for 1 month in babies of vaccinated women. In a linear mixed model, 99% of babies of vaccinated mothers had lost their maternal antibodies after six months, compared to 95% of babies of naturally immune women. Breast feeding, parity, gestational age, birth weight, educational level, day care attendance and cesarean section were not significant in the model.

The findings are consistent with earlier studies showing that measles susceptibility is growing every year, Dr. Leuridan said. Yet, she added, "it is quite new that it is such a large gap."

Part of the reason for the expanding gap, she said, could be the increasing age of mothers and the general success of immunization in lowering overall exposure to the virus.

Dr. Archana Chatterjee, of Creighton University School of Medicine in Omaha, Nebraska, said current immunization practice is based on the theoretical assumption that maternal antibodies might interfere with the necessary replication of the vaccine virus.

She called the new study "food for thought," noting that larger studies are needed before considering guideline changes. For instance, small amounts of maternal antibodies that went undetected in the study in principle might interfere with the vaccine, she said.

Still, Dr. Chatterjee said, "it certainly is something that gives us pause."

http://www.bmj.com/cgi/content/abstract/340/may18_2/c1626
BMJ 2010.