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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
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today
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