A global resurgence of whooping cough, which is at epidemic levels in New Zealand, may have been made worse due to the current vaccine offering reduced protection compared with an older version, new research suggests.

However, the Ministry of Health says epidemics of the disease occur every four or five years, and this latest epidemic, which started in August last year, was not unexpected.

New Zealand changed its vaccine in 2000 and there has been at least one outbreak since then, in 2004/5 when 5000 cases were reported.

The study found that children vaccinated against the whooping cough with the current vaccine were three times more likely to develop the respiratory infection than children who received an earlier version.

Auckland University's Immunisation Advisory Centre vaccinology senior lecturer Dr Helen Petousis-Harris said it was difficult to know whether that was the case in New Zealand.

While reported cases may have increased since 2000, that couldn't necessarily be attributed to the new vaccine as there were now new ways of testing it.

"We're more likely to go looking for it now," she said.

However, she wasn't surprised by the study as there was a general awareness that while the new vaccine may not be as effective as the old one, it causes far less reactions.

Most industrialised countries, including Australia, the United States and the United Kingdom used the same vaccine as New Zealand, she said.

The old vaccine commonly caused reactions such as redness, swelling, and pain at the injection site, and, less frequently, caused fever and prolonged crying.

"So it's one of those trade-offs. I think the protection doesn't last as long either. That's one of the problems we are having in controlling pertussis, or whooping cough," Petousis-Harris said.

"The protection wanes. It wanes if you've had the disease, it wanes if you've had the old vaccine and it wanes if you've had the new vaccine, but it wanes a little faster with the new vaccine."

Whooping cough was a highly contagious bacterial infection spread by coughing and sneezing.

While the infection was generally milder in adults, some adult's coughs could be so severe they could break ribs or get bloodshot eyes, Petousis-Harris said.

But it was far more dangerous, and potentially life-threatening, if passed on to vulnerable babies.

There were 2966 whooping cough cases reported in New Zealand from the beginning of the year to July 20, including 1096 confirmed cases.

Last year, there were only 425 cases reported in the same period.

Canterbury had the highest number of cases in the two weeks to July 20 with 35, while Waikato and Capital and Coast (Wellington) had 21 cases each.

Queensland's recent study supported Petousis-Harris' view, showing that though the current vaccine was less effective it was known to be safer with fewer side effects than its predecessor.

"These findings could go some way to explaining why we are currently seeing a resurgence of pertussis in younger age-groups in Australia," Queensland Children's Medical Research (QCMRI) Institute senior research fellow associate professor Stephen Lambert said.

"In making the switch in vaccines in 1999 we may have traded off some of the protection whole cell vaccines provided in exchange for a better tolerated vaccine."

"Looking at the bigger picture, it shows us that we don't yet have the perfect whooping cough vaccine and it gives us cause to work toward developing a more effective as well as a safe vaccine for whooping cough."

Lambert said clinicians should not exclude whooping cough as a diagnosis just because a child had all of their vaccinations.

He advised parents that it was still "absolutely crucial" for them to vaccinate their children.

"Those who are unlucky enough to get whooping cough after being vaccinated will have a milder illness for a shorter period of time and be less infectious to others than those who have not received the vaccine," Lambert said.

The study by University of Queensland, QCMRI and the Royal Children's Hospital was published in the Journal of the American Medical Association overnight.

It looked at more than 40,000 Queensland children born in 1998 who were vaccinated against whooping cough.

WHOOPING COUGH IN NEW ZEALAND

Vaccinations against whooping cough were given in three rounds, usually when children were six weeks, three and five months old and followed by boosters when they are four and 11. They are free in New Zealand.

However, they do not fully protect children from the disease, with about 16 per cent not being fully protected.

Epidemics usually occur every four or five years, according to the Ministry of Health. More than 5000 cases were recorded during the last epidemic in 2004-2005, which resulted in 139 children being hospitalised and the death of one child.

Whooping cough can last for three months and is infectious in the first three weeks. It can lead to pneumonia, convulsions, brain damage and death. It can be treated with antibiotics.

- © Fairfax NZ News

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