A study by Dr Cameron Grant, a paediatrician at Starship Children’s Hospital and Associate Professor in paediatrics at The University of Auckland, shows that New Zealand’s exceptionally high rate of hospital admissions for whooping cough (pertussis) decreased in the 2000s – the first decade to record a decrease since the 1960s.
New Zealand has a history of large and nasty whooping cough epidemics. Throughout the 1960s to 1990s, our rates of whooping cough remained well above Australia, the UK and US, despite the introduction here of a vaccine in 1945. Much of this can be put down to New Zealand’s low immunisation coverage, which was well below many developing countries. Whooping cough still kills about one child each year in New Zealand; most of those babies who die are under two months of age.
For his study, Dr Grant, whose PhD on pertussis in New Zealand infants was supported by the HRC and Cure Kids, calculated annual whooping cough discharge rates using national hospital discharge and census data. He then compared the average annual rate with previous decades. He says whooping cough hospitalisation admissions in the 2000s dropped by approximately 20 per cent compared with the 1990s.
“The Ministry of Health and the HRC funded research which underpinned the development of a national strategy to raise immunisation coverage levels in babies and young children,” says Dr Grant. “Improving immunisation delivery became a national health target in 2007, with the aim to have 95 per cent of children under two fully immunised by July 2012. A robust immunisation register was also developed. These initiatives have made a big difference. As of June 2012, 93 per cent of New Zealand children had received all of their scheduled doses of whooping cough vaccine.”
However, Dr Grant has words of caution. “While this recent decrease is very encouraging, we’ve still only made a small dent in the number of infants being admitted to hospital with whooping cough. Our infant admission rate remains three times higher than the rate in Australia.”
Dr Grant says now that we’ve shown that we can improve immunisation coverage, we have to shift our focus to making sure children are immunised on time. Children need to receive their immunisations for whooping cough at six weeks, three months, five months, and a booster at ages four and 11. “You have a five times greater chance of being hospitalised from whooping cough as an infant if your immunisation is delayed, and by delayed, I mean getting the three month dose when you’re four months old.”
So when might we be able to see whooping cough hospitalisation rates comparable to our Australian neighbours?
“I’d love to think that we’re not going to have kids die from this disease anymore, but it’s a really tricky disease. Breastfeeding doesn’t offer much protection, which is most unusual, and our natural immunity is incomplete. It’s also unbelievably infectious. Every case of whooping cough causes about 15 secondary cases, making it several times more infectious than influenza,” says Dr Grant.
“To get the disease rate down, we require high immunisation coverage and timely immunisation delivery which is sustained over a number of years. I think it’s going to take a decade or two more of doing what we’re doing – and continuing to do it well – before we can get hospitalisation rates comparable to Australia, the UK and US.”
Dr Grant says if you’d asked him five years ago if achieving a 95 per cent immunisation rate for children under two was possible, he wouldn’t have felt confident about saying yes. Today, he is.
“There’s so much more confidence now in the healthcare system. It’s been so exciting to see people who have been working in the immunisation area for a long, long time, saying ‘yes, what we’re doing is working.’”