Dutch study findings support earlier vaccination of newborns at high risk for measles

A new Dutch study suggests that infants born to mothers who received the measles-mumps-rubella (MMR) vaccine lose their initial immunity to measles--acquired from their mothers--sooner than infants born to mothers who were naturally infected with measles. The findings support earlier measles vaccination of infants where risk of exposure to measles is high, including some developed countries, such as in parts of Europe experiencing outbreaks, or in infants who will be travelling to areas where measles is still endemic, in line with current recommendations, according to the study published in The Journal of Infectious Diseases and now available online.

Newborns are protected from measles, mumps, and rubella during their first few months of life by antibodies they receive from their mothers. An infant's level of immunity is based, in part, on the mother's blood antibody level. A child's first dose of MMR vaccine is usually administered at around age one. Prior to the first vaccination, however, an infant's immunity begins to wane. Previous studies have demonstrated that mothers who received MMR vaccination tend to have a lower concentration of measles-specific antibodies compared to mothers who naturally acquired measles infection. As a result, babies born to mothers who received the MMR vaccine have a shorter duration of protection and may remain unprotected for a period of time before they receive the first vaccination.

The combined measles-mumps-rubella vaccine has been successfully administered in many developed countries for over twenty years and has significantly decreased the incidence of infection. In fact, measles is considered eliminated in the Americas, although limited outbreaks connected with measles infection imported by travelers from other countries still occur. In the Netherlands, measles vaccination of young children was introduced in 1976 and the combined MMR vaccine was introduced in 1987. However, a portion of the Dutch population refuses vaccination based on religious beliefs, and endemic measles, mumps, and rubella outbreaks still occur in the country and in other parts of Europe. Sandra Waaijenborg, PhD, and colleagues from the National Institute of Public Health and the Environment in the Netherlands studied the duration of protection against measles, mumps, and rubella by comparing antibody levels in infants in the general Dutch population with those of infants in orthodox protestant communities, where more mothers refuse vaccination, in 2006/2007.

Dr. Waaijenborg and investigators studied blood samples from randomly selected Dutch infants and women of childbearing age and measured the concentration of antibodies against viruses, comparing them against a level that is considered protective against infection. They then compared antibody levels of the general population with those of the orthodox protestant community, where vaccination rates are low and outbreaks of measles, mumps, and rubella have been reported recently.

The researchers found that the duration of protection by passive immunity was shorter for infants born to mothers who received MMR vaccine than for infants born to mothers from a low vaccine coverage population. Duration of protection from measles was almost two months shorter for infants in the general public than for infants in the orthodox protestant communities. Tests for rubella also showed a lower concentration of antibodies in mothers who were vaccinated. Mumps showed no statistically significant differences in antibodies between the two populations. (Rubella and mumps are not typically seen in infants, and are generally not as severe, compared to measles, which is the leading cause of vaccine-preventable childhood mortality globally.)

With the proportion of European women of child-bearing age who have been vaccinated with MMR expected to increase in the coming years, "we expect that this will further shorten the duration of protection of infants by maternal antibodies against measles and rubella, and that shortening of duration of protection of infants by maternal antibodies against mumps will become more detectable in the near future," the authors wrote. With the first vaccinated cohort of the European population now having children, "a new unanticipated pool of individuals that are susceptible to infection" is being created, said Dr. Waaijenborg.

The authors conclude that the age of first MMR immunization may need to be earlier where exposure to measles is high, including in some developed countries, such as parts of Europe. The study authors suggest temporarily lowering the age for the first dose of MMR vaccine for those children whose risk of exposure to measles is high, such as in areas with an ongoing outbreak, or when the child will be travelling to regions where the disease is endemic, in line with current recommendations. As the number of babies born to mothers who have received the MMR vaccine will continue to increase rapidly in the developed world, the authors also urged additional study of the duration of protection in young infants over the next decade.

In an accompanying editorial, Hayley A. Gans, MD, and Yvonne Maldonado, MD, of Stanford University School of Medicine highlighted the importance of controlling measles in young infants, which results in 164,000 deaths globally per year. Given the potential for a growing population of infants who are susceptible to vaccine-preventable diseases, the editorial authors suggest that early immunization may be the most effective strategy for protection during the first year of life, in settings where the risk of exposure to measles is high. "Such a strategy must be pursued within the context of better defining the developing infant immune system," they added, underscoring the need for additional research to provide better measures of vaccine efficacy in infants.

Fast Facts:

1) Before being vaccinated at around one year of age, newborns are protected from measles, mumps, and rubella during their first few months of life in part by antibodies they receive from their mothers.

2) A new Dutch study suggests that infants born to mothers who themselves received the measles-mumps-rubella (MMR) vaccine in the Netherlands lose this initial immunity to measles sooner than infants born to mothers who were naturally infected with measles.

3) The duration of protection from measles was almost two months shorter in infants in the general Dutch public, where MMR vaccine is widely accepted, than in infants born in orthodox protestant communities, where the vaccine is not widely used.

4) Infants at high risk for measles, such as those in areas with ongoing endemic outbreaks or those who will be travelling to areas where measles is endemic, may need to receive their first MMR vaccination earlier, as current guidelines recommend.