Research aims to extend pertussis immunity to very young babies

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Pioneering research led by VIRGo aims to extend pertussis immunity to very young babies. This world-first study is part of a multi-pronged response to a national epidemic of pertussis (also known as whooping cough), a highly infectious, potentially fatal respiratory disease.

VIRGo, the Vaccine and Immunisation Research Group, is part of the Melbourne School of Population and Global Health at the University of Melbourne and a joint unit within the Murdoch Childrens Research Institute. With colleagues from the Universities of Sydney, Adelaide and Western Australia, Professor Terry Nolan, who heads both VIRGo and the School, is a principal investigator on the world’s first full-scale trial to measure the effectiveness of immunising babies against pertussis soon after birth. ‘Whooping cough’ is named for the sound sufferers emit as they gasp for oxygen after a sustained coughing fit caused by the disease.

Funded by the National Health and Medical Research Council (NHMRC), this collaboration involves three other research centres around Australia. A two-year successful recruitment of 440 mothers and babies was recently completed. Babies’ antibody levels will be measured until they are eight months of age, to ensure that their immunity is not subsequently lowered in response to this very early immunisation. The results are expected to be available in early 2013.

VIRGo is also planning research that would stretch protection from pertussis even further – before birth – by immunising pregnant mothers with a pertussis vaccine in their final trimester. “This is in the hope that the antibodies the mother generates will both protect her and will be passed through the placenta to her baby, giving the baby adequate levels of antibody to protect them before they start their regular course of pertussis vaccination after birth,” Professor Nolan says.

Complementary research, using mathematical modelling that explores the dynamics of population immunity, will be a crucial tool in assessing the success of the current vaccination schedule, he says. Australia’s national immunisation program over the past 20 years using new, improved vaccines had effectively controlled pertussis, achieving coverage rates of 90 per cent-plus across the population, he says. “Then about two years ago an epidemic started around the country with levels of whooping cough notifications which we haven’t seen for 30 to 40 years.” A three-fold increase in overall notifications above the average annual rate occurred in 2009, with almost a five-fold increase in children aged under 10. A few deaths among babies aged under four months and a rise in pertussis-related hospitalisations focused media attention on the epidemic. The factors behind the alarming rise in pertussis notifications included improved diagnostic testing and the limited duration of immunity that the vaccines afforded, Professor Nolan says. The latter was already being countered by a range of immunisation strategies, including a program that started in 2003 targeted at adolescents. However, more recently, it was discovered that young children were getting pertussis because the immunity afforded by their vaccinations had worn off before their pre-school boosters and close family members were potentially exposing them to the disease. This prompted state governments to fund a strategy dubbed “cocooning”. The cocoon strategy immunises close family members in order to protect young babies, whose full immunity after a vaccination course does not take effect until six months of age.

“Mathematical modelling to explore the dynamics of population immunity is a key aspect of our group’s research,” Professor Nolan says. “We’re trying to understand how immunising one age group within the population can produce vulnerability in another age group, and the extent to which booster vaccinations or the timing of those boosters are likely to produce optimal control.” Led by Associate Professor Jodie McVernon, the modelling study is being done in collaboration with the National Centre for Immunisation Research and Surveillance at the University of Sydney.

The potential intervention to protect very small babies in the womb by immunising their mothers in the last trimester of pregnancy is hoped to start in 2013.