Whooping cough bug evades vaccine in Australia

Whooping cough is not a pleasant experience--it's painful for the sufferer, can be life-threatening, particularly in young babies, and is distressing for families and careers. It's been well-controlled by vaccines since the 1950s, but some data coming out of Australia are cause for concern: It seems that the prolonged whooping cough epidemic that's swept the country is caused by a new strain that is evading the protection given by the vaccine.

Australia's current whooping cough epidemic began in 2008, with around 38,000 cases in 2011. To try to find out what was happening, a team of Australian scientists, led by the University of New South Wales, analyzed about 200 samples from patients diagnosed with whooping cough between 2008 and 2010. They found a new strain that carried different antigens on its surface. While the increase in numbers overall may partly be based on better diagnostics, the new strain caused less than a third of the cases in the decade before the current whooping cough epidemic and jumped almost three-fold to 84% by 2010.

Australia uses an acellular version of the whooping cough vaccine with three to 5 antigens, and these do not match those on the new strain so do not trigger a response. The vaccine hasn't caused the whooping cough bug to mutate, but because there is little or no immunity to this particular strain of Bordetella pertussis, it has been able to spread very easily. The country previously used a whole cell vaccine--there were safety concerns associated with this, but the vaccine did include hundreds of different antigens, reducing the chance of bacteria evading its coverage.

"The vaccine is still the best way to reduce transmission of the disease and reduce cases, but it appears to be less effective against the new strain, and immunity wanes more rapidly. We need to look at changes to the vaccine itself or increase the number of boosters," said Associate Professor Ruiting Lan, one of the study's authors.

The emerging strain has also been seen outside Australia, which raises the specter of a worldwide epidemic--whooping cough is highly infectious, and the world population is now very mobile, so someone catching the infection in Australia one day could be spreading it in Norway the next. This suggests the need for new vaccines, with a broader spectrum of antigens, or a change in vaccination strategy.

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