Resistance To Whooping Cough Vaccine Growing

(Reuters Health) - The bacterium that causes whooping cough is mutating to develop resistance to the vaccine used to immunise Dutch schoolchildren against the disease, researchers report.

"It seems like the bacterium is changing part of its coat, thereby disguising itself'' from the immune system, according to Dr Audrey King of the National Institute of Public Health and the Environment in the Netherlands.

She presented the findings to the American Society for Microbiology.

Until the advent of the pertussis (whooping cough) vaccine in the early 1950s, the respiratory illness was a major cause of illness and death, especially among infants and small children. Since the introduction of the vaccine (usually administered as part of the diptheria-tetanus-pertussis combo vaccine), rates for whooping cough have dropped dramatically in the developed world.

However, in recent years whooping cough has been making something of a comeback in the Netherlands, the United States and elsewhere. Comparing old and new strains of the Bordetella pertussis bacterium under the microscope, King and her colleagues found that, over time, ``at least two proteins located on the outside of the bacterium have been changed.''

Since vaccines work by "priming'' the human immune system to recognise (and attack) such proteins, these changes could explain why the pertussis vaccine now provides Dutch children with weaker protection against whooping cough than it did in years past.

This theory was supported by further studies in mice. After administering the vaccine to a group of mice, King's team infected them with either an older or present-day version of the whooping cough bacterium. The result? More mice infected with current strains of pertussis showed signs of illness than those infected with strains dominant in years past.

King stresses that the whooping cough vaccine remains "effective against serious disease,'' and there is no cause for immediate alarm. And she said it is difficult to say whether vaccines used in other countries share deficiencies similar to the form of the vaccine used in the Netherlands.

"However, there is still room for improvement,'' King adds, because whooping cough vaccines currently in use may not protect children from less serious forms of illness.

She recommends children receive booster shots of new and improved vaccines -that recognise the bacteria's altered "coat''- in those countries where they are available.

24/05/01

Further reading

Whooping Cough (Pertussis) - Xtra Health guide
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