A new strain of whooping cough has increased its prevalence and is now dominating Australia's four-year-long epidemic of the respiratory infection, a new study says. The strain has also been found in other countries, indicating it has the potential to spark epidemics elsewhere, too, the researchers say.
The Australian study found the share of whooping cough cases caused by the new strain has jumped in Australia from 31 percent to 84 percent in the last 10 years.
The finding suggests there is a need to alter the current version of the whopping cough vaccine, which was introduced in 1997, the researchers say.
"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," said study researcher Ruiting Lan, an associate professor at the University of New South Wales. "We need to look at changes to the vaccine itself or increase the number of boosters."
Whooping cough, or pertussis, is a bacterial infection of the respiratory tract that causes severe coughing, according to the National Network for Immunization Information. The coughing makes it difficult to breathe, and a "whooping" sound is sometimes heard when an afflicted child tries to breathe. Infants are most at risk for dying from the disease.
Australia has been experiencing a whooping cough epidemic since 2008. Children ages 5 to 9 have been most severely affected, despite that the fact that vaccination coverage in this age group has not changed over the last eight years, the researchers say.
An older version of the whooping cough vaccine, known as the whole cell pertussis vaccine, was less pure but contained many more antigens, or proteins for the body to develop immunity to, Lan said. Because of concerns about vaccine side effects, doctors switched to a more purified version, known as the acellular vaccine (ACV), in 1997. This version has only three to five antigens, Lan said.
"If the ACV is less effective against these new strains, we need to ask what other strategies can be used to combat the epidemic, which is ongoing," Lan said.
The rise in Australian cases also may be due in part to an increase in identification of disease cases as well as less-than-optimal vaccine coverage in the population.
The new study was published online in the Journal of Infectious Diseases.
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