After analysing strains of bacterium Bordetella pertussis that causes whooping cough, a UNSW-led team of researchers discovered that the bacterium now does not produce an important protein called pertactin.
Pertactin is one of the three proteins made from purified extracts of Bordetella pertussis bacteria and found in the vaccine in Australia. The absence now makes the vaccine less effective in fighting the disease.
"It's like a game of hide and seek. 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," said senior author of the study and associate professor Ruiting Lan of the UNSW School of Biotechnology and Biomolecular Sciences.
He added that now the newly evolved strains which lack protein pertactin have gained an advantage over those that contain pertactin.
The team also found out that around 80 per cent of the whooping cough cases in 2012 in Australia were caused by strains that lacked pertactin. In 2008, the pertactin-free bacteria were found in 5 per cent cases, while the figure in 2012 rose to 78 per cent.
"Vaccination is still the only way to protect against whooping cough, especially for the youngest babies who are most at risk of severe illness," Lan said.
Researchers said the finding does not point to the fact that pertactin-free whooping cough bacterium is more harmful than other strains. They said that they do not know whether the change was a short-term one or a long-term.
From 2008 to 2012, 148,000 cases of whooping cough were reported in Australia.
The study was published in Emerging Infectious Diseases.