There appears to be a gap in the protection against measles for young infants aged 2 to 3 months until 12 months of age (when they are vaccinated), say Belgian researchers in a report published today in the British Medical Journal (BMJ).

Measles antibody levels in infants, which they get from their mothers, fall over time, leaving them susceptible to the disease until they are vaccinated. These findings underline the importance of measles vaccination at around 12 months of age and support ongoing research into earlier vaccination.

The study involved 207 healthy mothers and their babies from five different hospitals in the Province of Antwerp, Belgium from April 2006.

The researchers looked at the mothers’ medical records and divided them into two groups:

  • Those who had received the measles vaccination during infancy.
  • Those with naturally acquired immunity from measles infection earlier in life.

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

The scientists report that the naturally immune mothers had considerably more antibodies than those who had been vaccinated. The same applied to their babies – babies of vaccinated mothers had significantly lower antibody levels than infants of naturally immune women.

Maternal antibodies lasted a median time of 2.61 months. 3.78 months for the offspring of naturally immune women, and 0.97 months for infants of vaccinated mothers.

99% of the infants of vaccinated mothers had lost all their maternal antibodies by the time they were six months old (95% of infants of naturally immune women). At 9 to 12 months of age none of the infants had any antibodies left.

Breastfeeding had no significant impact on measles antibody levels or duration, the scientists reported. Neither did birth weight, educational level, caesarean section or day care attendance.

This study describes a very early susceptibility to measles in both infants of vaccinated women and women with naturally acquired immunity, say the authors. If future studies show that measles vaccines can be offered with success at an age of less than nine months, policy makers could consider moving forward the routine measles vaccination programme.

For the moment, they suggest 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.
E Leuridan, N Hens, V Hutse, M Ieven, M Aerts, P Van Damme
BMJ 2010;340:c1626

Written by Christian Nordqvist