According to researchers, these findings should lead to reconsideration of the policy for vaccination during measles outbreaks and in humanitarian emergencies.
During the first months of life, maternal antibodies protect against measles and infants routinely receive their first vaccination between 9 and 15 months to coincide with when these maternal antibodies are lost.
This vaccination policy was based on children born to naturally infected mothers.
However, measles vaccination campaigns over the past 20-25 years in low-income countries have resulted in many mothers being immunised and transferring only half the maternal measles antibodies as naturally immune mothers.
ikewise, HIV positive mothers transfer a smaller number of antibodies than HIV negative mothers and HIV positive children also lose their protective maternal antibodies early.
As a result, a new group of children now exist who may lose their protection by 3 to 5 months of age and there may well be a need to provide measles vaccination at an earlier age.
An outbreak of measles in Guinea-Bissau in Africa offered Professor Peter Aaby and colleagues a unique opportunity to assess the protective effect of earlier vaccination at 4.5 months.
1333 infants were randomised to receive either measles vaccination at 4.5 months of age (441) or nothing (892). At 9 months of age all children received a measles vaccination.
Researchers collected blood samples to assess levels of maternal antibodies levels against measles at 4.5, 9, and 24 months of age in the early vaccination group and at 9, 18, and 24 months of age in the control group.
They found that early vaccination at 4.5 months of age offered more than 90 percent protection against measles infection and 100 percent protection against measles hospitalisation.
Before the initial vaccination at 4.5 months of age only 28 percent of the children had protective levels of maternal antibodies against measles. After this early vaccination 92 percent had measles antibodies at 9 months of age.
The researchers found that children vaccinated at 4.5 months and 9 months were better protected than those vaccinated only at 9 months.
The monthly incidence of measles was 0.7 percent in the children who received two doses and 3.1 percent in the children who received one dose at 9 months.
"If elimination of measles is planned it will be necessary in Africa to immunise as early as possible for many years", BMJ.com quoted the authors, as saying.
The study was published on BMJ.com today.