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Whooping cough vaccine may have lost its punch as bacterium evolves

 Australian study showed 80% of cases were free of the protein needed for vaccine's efficacy

The vaccine used to immunise against whooping cough might have bred a more evolved strain of the disease.

Researchers from the University of NSW say Bordetella pertussis, the bacterium that causes the potentially deadly illness, appears to have evolved to overcome the vaccine used to fight it.

That vaccine works by locating a protein called pertactin, which had been identified as one of the key elements of the disease.

But the study showed that about 80% of Australian whooping cough cases in 2012 were pertactin-free.

“It is harder for the antibodies made by the body's immune system in response to vaccination to 'search and destroy' the whooping cough bacteria which lack pertactin,” the senior author, Associate Professor Ruiting Lan, said. “It's like a game of hide and seek.”

The pertactin-free whooping cough strain might have gained a selective advantage over those carrying the protein, he said. He said pertactin-free whooping cough cases had also been found in France and the United States. “The fact that they have arisen independently in different countries suggests this is in response to the vaccine,” said Lan. But he stressed that although it may prove more elusive to the vaccine, there was no current evidence the new strain is deadlier.

It is also unclear whether the new strain reduces the effectiveness of the vaccine and, if so, for how long. Between 2008 and 2012, there were about 142,000 cases of whooping cough detected in Australia. The disease can also be especially dangerous for babies and may cause feeding or breathing difficulties, pneumonia, brain damage or death.

The study, which analysed more than 300 bacteria samples from across Australia, was published in the Emerging Infectious Diseases journal.