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Better monitoring and surveillance is crucial to combat the unpredictable bouts of measles epidemics that occur in Niger, concludes a study.
In a paper published in Nature yesterday (7 February), an international team of scientists investigate why measles epidemics in Niger — particularly in the capital Niamey — emerge in an erratic way.
In contrast, epidemics in cities in industrialised countries with comparably high birth rates occur annually, with more predictable timing.
The study found that, in Niamey, epidemics peter out at the start of the annual rainy season around February/March, and there is no knowing when the virus will reappear.
There can be periods of unpredictable length without any measles outbreaks, during which more children are born, which, due to their lack of immunity, fuels larger outbreaks when the virus does re-emerge.
The study suggests that large, variable outbreaks may still occur even as vaccine coverage is increased, according to Matthew Ferrari, one of the researchers from the Centre for Infectious Disease Dynamics at Pennsylvania State University in the United States.
"This highlights the need for monitoring and for reactive vaccination and treatment strategies as complementary policies," he says, adding that the basic message ‘vaccinate early, vaccinate often’ has not changed.
The researchers also highlight the importance of a routine vaccination programme that increases the immunity of the overall community — known as ‘herd’ immunity — and say this has to be supported by supplementary vaccination activities as well as by strategies that are more reactive to sudden outbreaks.
The researchers recommend ongoing surveillance to detect a coming epidemic and that this needs to be stepped up from September to November each year when the rainy season ends — historically a time of high transmission.
Ferrari says the study highlights the importance of setting policies based on local data, rather than solely on those with historical — usually European and North American — precedent.
Jeffrey Mphahlele, head of virology at the University of Limpopo in South Africa, says it is imperative that local data is used if measles vaccination programmes are to be successful.
"Measles vaccination protocols are pretty standard worldwide — that is to vaccinate babies at nine and 18 months. However there have to be exceptions to this when there is an outbreak of the virus."
Nature 451, 679 (2008)