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Whooping cough bacteria may evade vaccine -

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Whooping cough bacteria may evade vaccine

Jennifer Macey reported this story on Thursday, February 11, 2010 12:45:00

ELEANOR HALL: Australian GPs are urging people to get up to date on their flu and whooping cough
shots.

But scientists are raising concern about the effectiveness of the vaccine for whooping cough,
saying it may be losing its effectiveness because the bacteria is evolving.

New South Wales researchers have just discovered two new mutated strains of the bacteria, as
Jennifer Macey reports.

JENNIFER MACEY: Last year there were almost 30,000 cases of whooping cough - the most ever
recorded. In New South Wales three babies died from the disease.

Dr Jane Smith is a GP on the Gold Coast. She says it's a terrible illness in young children.

JANE SMITH: They have bouts of coughing where they cough and they go (sound of coughing and
whooping) at the end of it but it's much, much worse than that, often followed by vomiting.

That's what can lead to death. It's the respiratory. It's the difficulty breathing that really
leads to their death.

JENNIFER MACEY: To find out why there was an increase in infections a team of scientists looked at
the bordetella pertussis bacteria behind the disease. They discovered that the two most common
strains of the bacteria have mutated.

Associate professor Ruiting Lan from the University of New South Wales led the study.

RUITING LAN: We identified two strains that have increased in frequency. Then we looked at the
genes in these two types of strains for those genes that encoding the antigens and we found
mutations in them.

JENNIFER MACEY: The research has been published in the journal Emerging Infectious Diseases.

Professor Lyn Gilbert is a clinical microbiologist at the University of Sydney who was also
involved in the study. She says it's unclear why the bacteria is evolving.

LYN GILBERT: Bacteria change and mutate all the time. They're very flexible. They, sometimes
because people become immune, large number of the population becomes immune and they may change to
bypass that sort of immunity.

Sometimes it happens just spontaneously.

JENNIFER MACEY: Do you think this one is due to interventions such as vaccination? Do you think
it's because there is now widespread vaccination of whooping cough?

LYN GILBERT: People have been concerned that this might be a possibility but up until now there's
really been no evidence for that. And there are lots of other potential explanations for why
pertussis continues to occur in the population.

JENNIFER MACEY: But the mutation seems to coincide with the changes to the type of whooping cough
vaccines used in Australia.

Before 1997 a whole cell vaccine made up of hundreds of antigens was used but it also had more side
effects such as fever and irritability.

Professor Lan says an acellular vaccine made up of only three or five antigens is now more common.

RUITING LAN: For the acellular vaccine they are only three to five antigens. Because there are a
smaller number of antigens the bacteria would have an easier target to escape from the vaccine or
to make the vaccine less effective. If they mutate their genes they are encoding for those
antigens.

JENNIFER MACEY: The concern is that the current vaccine may no longer protect against the mutated
strains.

But professor Gilbert says more research is needed to prove this. She says parents and their
children should still get immunised.

LYN GILBERT: Because these strains are only a minority of the total number of different strains.
There are several strains that circulate and they may well change again.

And despite this finding we don't know that these new strains are more likely to cause infection in
immunised people. All we know is that they've appeared recently.

So we don't know that the vaccine is less effective against them and that's what we have to
determine.

And it's all the more important that people get immunised and have the boosters when they need to
because it's that partial immunity that occurs in older people that they're most at risk of getting
an atypical infection and then potentially passing it on to a child, a baby who hasn't been
immunised because they're too young.

ELEANOR HALL: That's professor Lyn Gilbert from the University of Sydney ending that report by
Jennifer Macey.