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Babies aged 2-3 months to a year vulnerable to measles

Immunity to measles disappears long before vaccination at one year old

OnMedica staff

Wednesday, 19 May 2010

Babies seem to be unprotected from measles between about 2-3 months old until they are vaccinated at 12 months, finds research published on bmj.com.

The protection from measles that a baby has from its mother’s antibodies falls very quickly in the first few months of life, even if they are breastfed, leaving them susceptible to infection until they are vaccinated, usually at 12 months old. Babies of vaccinated mothers are protected for a shorter time than babies whose mothers have natural immunity (from infection).

The authors of the study say their results underline the importance of measles vaccination at around 12 months of age and support ongoing research into earlier vaccination.

They investigated 207 healthy women-infant pairs in Antwerp, Belgium. Women were divided into two groups: those who had had measles vaccination as babies, and those who had acquired immunity to measles naturally, through infection.

Levels of measles antibodies were measured from blood samples taken during week 36 of pregnancy, at birth (cord blood), in all infants at 1, 3 and 12 months, and randomly at either 6 or 9 months.

Significantly fewer antibodies were found in vaccinated women’s blood than in naturally immune women, and this also affected their babies’ immunity: infants of vaccinated women had significantly lower antibody levels than babies of naturally immune women.

Maternal antibodies were present for a median time of 2.61-3.78 months in infants of naturally immune women, and just 0.97 months in infants of vaccinated women.

By six months old, almost all babies had lost their maternal antibodies (>99% of infants of vaccinated women and 95% of infants of naturally immune women). At 9 and 12 months, no positive samples were found in either group.

Breastfeeding, birth weight, educational level, caesarean section or day care attendance had any significant impact on the duration of maternal antibodies.

The authors say that their study shows that infants become susceptible to measles at a very young age, whether their mothers were immune through vaccination or infection. They suggest that if future studies show that measles vaccine can be offered with success when babies are younger than nine months, the routine measles vaccination programme could be brought forward.

In the mean time, they say that early vaccination should be considered during an outbreak or after contact with siblings with measles, and for infants travelling or migrating to endemic areas.

“Most importantly, we confirm the extreme importance of timely administration of the first dose of measles vaccine,” they conclude.

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