THE bacteria that causes whooping cough in Australia has mutated, scientists have warned, eroding the protection provided by the vaccine now given to children.
Researchers from the University of New South Wales have identified significant changes in the two most common strains of the Bordetella pertussis bacteria, which they also traced back to events in the late 1990s.
Australian children were given a broad-acting "whole cell" vaccination against whooping cough up to 1997, but this was phased out over two years and replaced with a more targeted version. Concerns over potential side-effects were behind the change over to a vaccine with a narrower scope, but this now appears to have contributed to the promotion of resistant strains.
"A key issue is that the whole cell vaccine contained hundreds of antigens, which gave broad protection against many strains of pertussis," said Associate Professor Ruiting Lan of the UNSW School of Biotechnology and Biomolecular Sciences.
"But the (targeted) acellular vaccine contains only three to five antigens.
"Our findings suggest that the use of the acellular vaccine may be one factor contributing to these genetic changes."
The research team analysed more than 200 samples of the bacterium collected over the past 40 years in Australia, and these were compared with samples from Japan, Canada, USA and Finland.
They found while the vaccine now in use was effective against some of the strains circulating in Australia it may no longer protect against two strains, known as MT27 and MT70.
Dr Lan said more research was needed to confirm the results but health authorities may need to modify the vaccine to broaden the protection it offered, "or over time it could lose effectiveness as the organism evolves".
The discovery comes amid an increase in whooping cough cases in Australia, with several significant outbreaks seen last year in western Sydney.
Protection against whooping cough is contained in the range of childhood vaccinations which, in NSW, are usually given to infants at two, four and six months. Parents who opt out of this child vaccination process were thought to have contributed to the rise in cases, along with improved diagnosis, and the mutation discovery adds a third potential contributor.
One in 200 infants who contract whooping cough before they turn six months will die of the infection