Children who are vaccinated closer to 15 months of age may gain better protection against measles compared with those who are immunized around 12 months of age.

Measles is a highly contagious viral infection that causes a rash, high fever, coughing and other symptoms. It can also lead to serious complications such as pneumonia and brain inflammation. Vaccination prevents most cases, and in the US, children receive two doses of the measles-mumps-rubella (MMR) vaccine. The first dose is given at 12 to 15 months of age and the second is given around 4 to 6 years of age to ensure adequate protection.

Researchers from the Mayo Clinic in Rochester, Minnesota evaluated 333 children who were immunized against measles at 12 months and 719 children immunized closer to 15 months. All of the children, who were between the ages of 6 and 11 years and from the US and Canada, had only one dose of measles vaccine in accord with recommendations at that time.

Overall, 87% of the US children and 76% of the Canadian children had measles-fighting antibodies in their blood. After adjusting for time from immunization and age of immunization, The researchers found that those children vaccinated closer to 15 months of age were more than twice as likely to have adequate protection against measles compared with children immunized at 12 months of age.

The authors note that children with a few more months of development appear to respond better to immunization and their immune system produces more antibodies against measles.

The current US policy of immunizing with the first dose of measles at the age of 12 months is less effective than a policy of immunizing at 12 to 15 months of age. These findings may be highly significant as we move toward an era in which measles exposure may be rare and policies are developed to eradicate measles.

Mayo Clinic Proceedings May 2002;77:446-452