Vaccination, surveillance needed for 'erratic' measles

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Vaccination, surveillance needed for 'erratic' measles

Childhood measles vaccination in rural Niger

Carol

8 February 2008

Source: SciDev.Net

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 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.

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. "

Link to full paper in Nature

Reference: Nature 451, 679 (2008)