The World Health Organization recommends routine vaccinations for measles at 9 months, but a new study published on bmj.com finds that an additional vaccination given at 4.5 months may also reduce measles outbreaks in developing countries. The authors of the research suggest that vaccination policies during measles outbreaks and in humanitarian emergencies should be adjusted or reconsidered.
During the first few months of life, infants are usually protected against measles by maternal antibodies. When these antibodies are lost, between 9 and 15 months, vaccinations are routinely administered. If a child is born to a naturally infected mother, this vaccination policy makes sense. However, in the past 20 to 25 years, measles vaccination campaigns have immunized many mothers, and they only transfer about half the maternal measles antibodies to their children compared to naturally immune mothers.
A similar pattern is seen with HIV. Compared to HIV negative mothers, HIV positive ones transfer fewer antibodies to their children, and HIV positive children lose their maternal antibodies earlier as well. This has led to a cohort of children who lose their protective maternal antibodies between 3 and 5 months, requiring vaccinations at an earlier age.
Professor Peter Aaby (Bandim Health Project) and colleagues analyzed vaccination policies during a measles outbreak in Guinea-Bissau, Africa. They randomized 1333 infants so that 441 received a measles vaccination at 4.5 months of age and 892 received nothing. After 9 months of age, all children received a measles vaccine per WHO recommendations. The researchers collected blood samples to measure maternal antibody levels against measles at 4.5, 9, and 24 months of age in the group vaccinated at 4.5 months and at 9, 18, and 24 months of age in group only vaccinated at 9 months of age.
The analysis revealed that vaccination at 4.5 months of age resulted in a 100% protection against being hospitalized for measles and an over 90% protection against measles infection. The researchers found that only 28% of children had the necessary maternal antibodies to protect against measles before the initial vaccination at 4.5 months. The second blood analysis at 9 months revealed that 92% of those who had the initial vaccination had measles antibodies.
Ultimately, vaccination at 4.5 months and 9 months provided better protection against measles than children vaccinated only at 9 months. Monthly incidence rates for measles also varied between the two groups: 0.7% for children who received the two vaccinations compared to 3.1% in the children who received one dose at 9 months.
The authors conclude that, “If elimination of measles is planned it will be necessary in Africa to immunise as early as possible for many years.”
In an accompanying editorial, Dr Hélène Broutin and Dr Mark A Miller (National Institutes of Health) write that, “The study is relevant and timely since it offers policy makers potential alternative vaccination strategies. Further research should include an assessment of age specific antibodies in infants throughout their first year of life, with control of HIV status and maternal exposure to natural infection with measles…These findings offer policymakers potential alternative vaccination strategies, but research is required to determine the possible immunosuppressive effect from live virus measles vaccines on other vaccine responses when given in early infancy.”
They conclude: “The current goal to achieve high vaccine coverage should not be separated from the need for more timely vaccination, especially in developing countries…[but] earlier measles vaccination should not substitute for the dose given to infants at ages 9 – 15 months, which increases overall immunity in the population.”
Protective efficacy of standard Edmonston-Zagreb measles vaccination in infants aged 4.5 months: interim analysis of a randomised clinical trial
Cesario L Martins, May-Lill Garly, Carlito Bale, Amabelia Rodrigues, Henrik Ravn, Hilton C Whittle, Ida M Lisse, Peter Aaby
BMJ (2008). 337: a661
doi:10.1136/bmj.a661.
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Written by: Peter M Crosta