A study suggests a whooping cough outbreak in New Zealand could have been worsened by the reduced effectiveness of the current vaccine.
Queensland research shows that a resurgence of the highly infectious disease around the world was due to the current vaccine offering reduced protection than an older version.
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.
Immunisation Advisory Centre vaccinology senior lecturer Dr Helen Petousis-Harris said today she was not surprised by the study.
"We generally thought that the vaccines that we use now may not be as effective as the old ones, but the old ones caused a lot more reactions."
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, if passed on to vulnerable babies it could be life-threatening.
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.